1. ASNT Level III- Visual & Optical Testing My Pre-exam
Preparatory Self Study Notes Reading 4 Section 1 2014-August
Charlie Chong/ Fion Zhang
2. Reading 4 ASNT Nondestructive Handbook Volume 8 Visual &
Optical testing- Section 1 For my coming ASNT Level III VT
Examination 2014-August Charlie Chong/ Fion Zhang
3. Fion Zhang 2014/August/15 Charlie Chong/ Fion Zhang
4. SECTION 1 FUNDAMENTALS OF VISUAL AND OPTICAL TESTING Charlie
Chong/ Fion Zhang
5. SECTION 1: FUNDAMENTALS OF VISUAL AND OPTICAL TESTING PART
1: Description of visual and optical tests 1.1 Luminous Energy
Tests 1.2 Geometrical Optics PART 2: History of the borescope 2.1
Development of the Borescope 2.2 Certification of Visual Inspectors
PART 3: Vision and light 3.1 The Physiology of Sight 3.2 Weber's
Law 3.3 Vision Acuity 3.4 Vision Acuity Examinations 3.5 Visual
Angle 3.6 Color Vision 3.7 Fluorescent Materials Charlie Chong/
Fion Zhang
6. PART 4: Safety for visual and optical tests 4.1 Need for
Safety 4.2 Laser Hazards 4.3 Infrared Hazards 4.4 Ultraviolet
Hazards 4.5 Photosensitizers 4.6 Damage to the Retina 4.7 Thermal
Factor 4.8 Blue Hazard 4.9 Visual Safety Recommendations 4.10 Eye
Protection Filters Charlie Chong/ Fion Zhang
7. Part 1: DESCRIPTION OF VISUAL AND OPTICAL TESTS 1.1.0
General: Nondestructive tests typically are done by applying a
probing medium (such as acoustic or electromagnetic energy) to a
material. After contact with the test material, certain properties
of the probing medium are changed and can be used to determine
changes in the characteristics of the test material. Density
differences in a radiograph or location and peak of an oscilloscope
trace are examples of means used to indicate probing media changes.
In a practical sense, most nondestructive tests ultimately involve
visual tests- a properly exposed radiograph is useful only when the
radiographic interpreter has the vision acuity required to
interpret the image. Likewise, the accumulation of magnetic
particles over a crack indicates to the inspector an otherwise
invisible discontinuity. The interface of visual testing with other
nondestructive testing methods is discussed in more detail in a
later section of this volume. Charlie Chong/ Fion Zhang
8. For the purposes of this book, visual and optical tests are
those that use probing energy from the visible portion of the
electromagnetic spectrum. Changes in the light's properties after
contact with the test object may be detected by human or machine
vision. Detection may be enhanced or made possible by mirrors,
magnifiers, borescopes or other vision enhancing accessories.
Keywords; Visible Spectrum (380nm ~ 770nm), Human or machine
vision, Vision enhancing tools- Borescope, mirror and other
enhancing accessories. Charlie Chong/ Fion Zhang
9. 1.2.0 Luminous Energy Tests Visual testing was probably the
first method of nondestructive testing. It has developed from its
ancient origins into many complex and elaborate optical
investigation techniques. Some visual tests are based on the simple
laws of geometrical optics. Others depend on properties of light,
such as its wave nature. A unique advantage of many visual tests is
that they can yield quantitative data more readily than other
nondestructive tests. Luminous energy tests are used primarily for
two purposes: 1. testing of exposed or accessible surfaces of
opaque test objects (including a majority of partially assembled or
finished products) and 2. testing of the interior of transparent
test objects (such as glass, quartz, some plastics, liquids and
gases). For many types of objects, visual testing can be used to
determine quantity, size, shape, surface finish, reflectivity,
color characteristics, fit, functional characteristics and the
presence of surface discontinuities. Charlie Chong/ Fion Zhang
10. Keywords: Objects: Testing of opaque objects Testing of
transparent objects VT is used to determined: quantity, size,
shape, surface finish, reflectivity, color characteristics, fit,
functional characteristics and the presence of surface
discontinuities. Question: Does VT covers Translucent object?
Charlie Chong/ Fion Zhang
11. 1.3.0 Geometrical Optics 1.3.1 Image Formation Most optical
instruments are designed primarily to form images. In many cases,
the manner of image formation and the proportion of the image can
be determined by geometry and trigonometry without detailed
consideration of the physics of light rays. This practical
technique is called geometrical optics and it includes the
formation of images by lenses and mirrors. The operation of
microscopes, telescopes and borescopes also can be partially
explained with geometrical optics. In addition, the most common
limitations of optical instruments can be similarly evaluated with
this technique. Keyword: Geometrical optics Charlie Chong/ Fion
Zhang
12. 1.3.2 Light Sources The light source for visual tests
typically emits radiation of a continuous or noncontinuous (line)
spectrum. Monochromatic light is produced by use of a device known
as a monochromator, which separates or disperses the wavelengths of
the spectrum by means of prisms or gratings. Less costly and almost
equally effective for routine tests are light sources emitting
distinct spectral lines, These include mercury, sodium and other
vapor discharge lamps. Such light sources may he used in
combination with glass, liquid or gaseous filters or with highly
efficient interference filters, for transmitting only radiation of
a specific wavelength. Keywords: Continuous spectrum Non-continuous
spectrum-Monochromatic light Monochromator used prisms or grating
Charlie Chong/ Fion Zhang
13. Keywords: Monochromatic light produces by vapor discharged
lamp (Mercury/sodium etc.) with glass/ liquid & gaseous filter
to produces only radition with specific wavelength Charlie Chong/
Fion Zhang
14. Gas-discharge lamps are a family of artificial light
sources that generate light by sending an electrical discharge
through an ionized gas, a plasma. The character of the gas
discharge depends on the pressure of the gas as well as the
frequency of the current. Typically, such lamps use a noble gas
(argon, neon, krypton and xenon) or a mixture of these gases. Most
lamps are filled with additional materials, like mercury, sodium,
and metal halides. In operation the gas is ionized, and free
electrons, accelerated by the electrical field in the tube, collide
with gas and metal atoms. Some electrons in the atomic orbitals of
these atoms are excited by these collisions to a higher energy
state. When the excited atom falls back to a lower energy state, it
emits a photon of a characteristic energy, resulting in infrared,
visible light, or ultraviolet radiation. Some lamps convert the
ultraviolet radiation to visible light with a fluorescent coating
on the inside of the lamp's glass surface. The fluorescent lamp is
perhaps the best known gas-discharge lamp.
http://en.wikipedia.org/wiki/Gas-discharge_lamp Charlie Chong/ Fion
Zhang
15. Compared to incandescent lamps, gas-discharge lamps offer
higher efficiency, but are more complicated to manufacture, and
require auxiliary electronic equipment such as ballasts to control
current flow through the gas. Some gas-discharge lamps also have a
perceivable start-up time to achieve their full light output.
Still, due to their greater efficiency, gas-discharge lamps are
replacing incandescent lights in many lighting applications.
Charlie Chong/ Fion Zhang
16. Vapor Discharged Lamp Charlie Chong/ Fion Zhang
17. Vapor Discharged Lamp Charlie Chong/ Fion Zhang
18. Vapor Discharged Lamp Charlie Chong/ Fion Zhang
19. A monochromator is an optical device that transmits a
mechanically selectable narrow band of wavelengths of light or
other radiation chosen from a wider range of wavelengths available
at the input. The name is from the Greek roots mono-, single, and
chroma, colour, and the Latin suffix -ator, denoting an agent.
http://en.wikipedia.org/wiki/Monochromator Charlie Chong/ Fion
Zhang
20. Monochromator used prisms or grating Charlie Chong/ Fion
Zhang
21. Monochromator used prisms or grating Charlie Chong/ Fion
Zhang
22. Monochromator used prisms or grating Charlie Chong/ Fion
Zhang
23. Monochromator used prisms or grating Charlie Chong/ Fion
Zhang
24. Monochromator used prisms or grating Charlie Chong/ Fion
Zhang
25. Monochromator used prisms or grating Charlie Chong/ Fion
Zhang
26. Monochromator used prisms or grating Charlie Chong/ Fion
Zhang
27. 1.3.3 Stroboscopic Sources The stroboscope is a device that
uses synchronized pulses of high intensity light to permit viewing
of objects moving with a rapid, periodic motion. A stroboscope can
be used for direct viewing of the apparently stilled test object or
for exposure of photographs. The timing of the stroboscope also can
be adjusted so that the moving test object is seen to move but at a
much slower apparent motion. The stroboscopic effect requires an
accurately controlled, intermittent source of light or may be
achieved with periodically interrupted vision. Charlie Chong/ Fion
Zhang
28. 1 Stroboscopic Movement Charlie Chong/ Fion Zhang
29. Stroboscopic Movement Charlie Chong/ Fion Zhang
30. Stroboscopic Movement Charlie Chong/ Fion Zhang
31. Stroboscopic Sources Charlie Chong/ Fion Zhang
32. Stroboscopic Sources Charlie Chong/ Fion Zhang
33. Stroboscopic Glasses Charlie Chong/ Fion Zhang
34. Charlie Chong/ Fion Zhang
35. Charlie Chong/ Fion Zhang
36. Charlie Chong/ Fion Zhang
37. 1.3.4 Light Detection and Recording Once light has
interacted with a test object (been absorbed, reflected or
refracted), the resulting light waves are considered test signals
that may be recorded visually or photoelectrically. Such signals
may be detected by means of photoelectric cells, bolometers or
thermopiles, photomultipliers or closed circuit television systems.
Electronic image conversion devices often are used for the
invisible ranges of the electromagnetic spectrum (infrared,
ultraviolet or X-rays) but they also may he used to transmit visual
data from hazardous locations or around obstructions. Occasionally,
intermediary photographic recordings are made. The processed
photographic plate can subsequently be evaluated either visually or
photoelectrically. Some applications take advantage of the ability
of photographic film to integrate low energy signals over long
periods of time. Photographic film emulsions can be selected to
meet specific test conditions, sensitivities and speeds. Charlie
Chong/ Fion Zhang
38. Keywords Photoelectricity detection photoelectric cells,
bolometers or thermopiles, photomultipliers or closed circuit
television systems. Charlie Chong/ Fion Zhang
39. Bolometer consists of an absorptive element, such as a thin
layer of metal, connected to a thermal reservoir (a body of
constant temperature) through a thermal link. The result is that
any radiation impinging on the absorptive element raises its
temperature above that of the reservoir the greater the absorbed
power, the higher the temperature. The intrinsic thermal time
constant, which sets the speed of the detector, is equal to the
ratio of the heat capacity of the absorptive element to the thermal
conductance between the absorptive element and the reservoir. The
temperature change can be measured directly with an attached
resistive thermometer, or the resistance of the absorptive element
itself can be used as a thermometer. Metal bolometers usually work
without cooling. They are produced from thin foils or metal films.
Today, most bolometers use semiconductor or superconductor
absorptive elements rather than metals. These devices can be
operated at cryogenic temperatures, enabling significantly greater
sensitivity. Charlie Chong/ Fion Zhang
40. Bolometer Charlie Chong/ Fion Zhang
41. Bolometer Charlie Chong/ Fion Zhang
42. Bolometer Charlie Chong/ Fion Zhang
43. Thermopiles Charlie Chong/ Fion Zhang
44. Thermopiles Charlie Chong/ Fion Zhang
45. Thermopiles Charlie Chong/ Fion Zhang
46. Multi-Junction Thermopiles The thermopile is a heat
sensitive device that measures radiated heat. The sensor is usually
sealed in a vacuum to prevent heat transfer except by radiation. A
thermopile consists of a number of thermocouple junctions in series
which convert energy into a voltage using the Peltier effect.
Thermopiles are convenient sensor for measuring the infrared,
because they offer adequate sensitivity and a flat spectral
response in a small package. More sophisticated bolometers and
pyroelectric detectors need to be chopped and are generally used
only in calibration labs. Charlie Chong/ Fion Zhang
47. Photo Detector Comparisons
http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/RYER/ch10.html
Charlie Chong/ Fion Zhang
48. Photomultiplier Photomultiplier tubes (photomultipliers or
PMTs for short), members of the class of vacuum tubes, and more
specifically vacuum phototubes, are extremely sensitive detectors
of light in the ultraviolet, visible, and near-infrared ranges of
the electromagnetic spectrum. These detectors multiply the current
produced by incident light by as much as 100 million times (i.e.,
160 dB), in multiple dynode stages, enabling (for example)
individual photons to be detected when the incident flux of light
is very low. Unlike most vacuum tubes, they are not obsolete. The
combination of high gain, low noise, high frequency response or,
equivalently, ultra-fast response, and large area of collection has
earned photomultipliers an essential place in nuclear and particle
physics, astronomy, medical diagnostics including blood tests,
medical imaging, motion picture film scanning (telecine), radar
jamming, and high-end image scanners known as drum scanners.
Elements of photomultiplier technology, when integrated
differently, are the basis of night vision devices. Charlie Chong/
Fion Zhang
49. Semiconductor devices, particularly avalanche photodiodes,
are alternatives to photomultipliers; however, photomultipliers are
uniquely well-suited for applications requiring low-noise,
high-sensitivity detection of light that is imperfectly collimated.
http://en.wikipedia.org/wiki/Photomultiplier Charlie Chong/ Fion
Zhang
53. Photoelectric Cell Photovoltaic Cell Photo emissivity
Photovoltaic's (PV) is a method of generating electrical power by
converting solar radiation into direct current electricity using
semiconductors that exhibit the photovoltaic effect. Photovoltaic
power generation employs solar panels composed of a number of solar
cells containing a photovoltaic material. Solar photovoltaics power
generation has long been seen as a clean sustainable[1] energy
technology which draws upon the planets most plentiful and widely
distributed renewable energy source the sun. The direct conversion
of sunlight to electricity occurs without any moving parts or
environmental emissions during operation. It is well proven, as
photovoltaic systems have now been used for fifty years in
specialized applications, and grid-connected systems have been in
use for over twenty years Charlie Chong/ Fion Zhang
54. Charlie Chong/ Fion Zhang
55. Photovoltaic Cell Charlie Chong/ Fion Zhang
56. Photovoltaic Cell Charlie Chong/ Fion Zhang
57. Photoemissive Cell- Photoemissive cell (electronics) A
device which detects or measures radiant energy by measurement of
the resulting emission of electrons from the surface of a
photocathode. Charlie Chong/ Fion Zhang
58. Photoemissive Cell Charlie Chong/ Fion Zhang
59. Photoemissive Cell: Analysis of sodium levels in junk food
by flame photometer
http://www.pharmatutor.org/articles/analysis-sodium-levels-junk-food-flame-photometer?page=0,2
Charlie Chong/ Fion Zhang
60. 1.3.5 Fluorescence Detection A material is said to
fluoresce when exposure to radiation causes the material to produce
a secondary emission of longer wavelength than the primary,
exciting light. Visual tests based on fluorescence play a part in
qualitative and quantitative inorganic and organic chemistry, as a
means of quality control of chemical compounds, for identifying
counterfeit currency, tracing hidden water flow and for detecting
discontinuities in metals and pavement. Charlie Chong/ Fion
Zhang
61. Fluorescence Detection Charlie Chong/ Fion Zhang
62. More Reading on Light Light Measurement Handbook
http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/RYER/index.html
http://homepages.inf.ed.ac.uk/rbf/CVonline/ Charlie Chong/ Fion
Zhang
63. Part 2: History of Borescope 2.1.0 Introduction Development
of the Borescope The development of self illuminated telescopic
devices can be traced back to early interest in exploring the
interior human anatomy without operative procedures. Devices for
viewing the interior of objects are called endoscopes, from the
Creek words for "inside view." Today the term endoscope in the
United States is applied primarily to medical instruments. Nearly
all of the medical endoscopes have an integral light source; some
incorporate surgical tweezers or other devices. Industrial
endoscopes are called horescopes because they were 'originally used
in machined apertures and holes such as gun bores. There are both
flexible and rigid, fiber optic and geometric light borescopes.
Keywords: Endoscopes Horescopes Charlie Chong/ Fion Zhang
64. 2.1.1 Cystoscopes and Borescopes In 1806 Philipp Bozzini of
Frankfurt announced the invention of his Lichtleiter (German for
"light guide"). Having served as a surgeon in the Napoleonic wars,
Bozzini envisioned using his device for medical research. It is
considered the first endoscope. In 1876, Dr. Max Nitze, a
urologist, developed the first practical cystoscope to view the
human bladder.' A platinum loop in its tip furnished a bright light
when heated with galvanic current. Two years later, Thomas Edison
introduced an incandescent light in the United States. Within a
short time, scientists in Austria made and used a minute electric
bulb in Nitze's cystoscope, even before the electric light was in
use in America. The early cystoscopes contained simple lenses but
these were soon replaced by achromatic combinations. In 1900,
Reinhold Wappler revolutionized the optical system of the
cystoscope and produced the first American models. The forward
oblique viewing system was later introduced and has proved very
useful in both medical and industrial applications. Direct vision
and retrospective systems were also first developed for cystoscopic
use. Charlie Chong/ Fion Zhang
65. Borescopes and related instruments for nondestructive
testing have followed the same basic design used in cystoscopic
devices. The range of borescope sizes has increased, sectionalized
instruments have been introduced and other special devices have
been developed for industrial applications. Charlie Chong/ Fion
Zhang
66. 2.1.2 Gastroscopes and Flexible Borescopes A flexible
gastroscope, originally intended for observing the interior of the
stomach wall, was first developed by Rudolph Schindler' and
produced by Georg Wolf in 1932. The instrument consisted of a rigid
section and a flexible section. Many lenses of small focal distance
were used to allow bending of the instrument to an angle of 34
degrees in several planes. The tip of the device contained the
objective and the prism causing the necessary axial deviation of
the bundle of rays coming from the illuminated gastric wall. The
size of the image depended on the distance of the objective from
the observed surface. It could be magnified, reduced or normal size
but the image was sharp and erect with correct sides. Flexible
gastroscopes are now available, with rubber tubes over the flexible
portion, in diameters of approximately 14 mm (0.55 in.) and 8 mm
(0.31 in.). Charlie Chong/ Fion Zhang
67. Flexible borescopes for industrial use are more ruggedly
constructed than gastroscopes, having flexible steel tubes instead
of rubber for the outer tube of the flexible portion. A typical
flexible borescope is 13 mm (0,5 in.) in diameter and has a 1 m (3
ft) working length, with flexibility in about 500 mm (20 in.) of
the length. Extension sections are available in 1, 2 or 3 m (3, 6
or 9 ft) lengths, permitting assembly of borescopes up to 10 m (30
ft) in length. In such flexible instruments the image remains round
and sharp when the tube is bent to an angle of about 34 degrees.
Beyond that limit, the image becomes elliptical but remains clear
until obliterated at about 45 degrees of total bending. Charlie
Chong/ Fion Zhang
68. Keywords: Conventional Borescope Bend angles & Images
34 Degree- Round and Clear 34 ~ 45 Degree- Elliptical but Clear
> 45 Degree- Obliterated Charlie Chong/ Fion Zhang
69. Digitized Borescope Charlie Chong/ Fion Zhang
70. 2.1.3 American Development of Borescopes After the early
medical developments, certain segments of American industry needed
visual testing equipment for special inspection applications. One
of the first individuals to help fill this need was George Sumner
Crampton. George Crampton (Fig. 1) was born in Rock Island,
Illinois in 1874. He was said to have set up a small machine shop
by the age of 10 and his first ambition was to become an electrical
engineer. He chose instead to study medicine and received his M.D.
from the University of Pennsylvania in 1898. While he was interning
at Pennsylvania Hospital, Crampton's mechanical and engineering
abilities were recognized and he was advised to become an oculist.'
He returned to the university, took a degree in ophthalmology and
later practiced in Philadelphia, Pennsylvania and Princeton, New
Jersey In 1921, the Westinghouse Company asked Crampton to make a
device that could be used to check for discontinuities inside the
rotor of a steam turbine (Fig. 2). Crampton developed the
instrument in his Philadelphia shop and delivered the prototype
within a week- it was the first borescope produced by his company.
Charlie Chong/ Fion Zhang
71. Crampton continued to supply custom borescopes for testing
inaccessible and often dark areas on power turbines, oil refinery
piping, gas mains, soft drink tanks and other components (Fig. 3).
Crampton soon was recognized for his ability to design and
manufacture borescopes, periscopes and other optical equipment for
specific testing applications. After retiring as emeritus professor
of ophthalmology at the university Crampton continued private
practice in downtown Philadelphia. At the same time, he worked on
borescopes and other instruments in a small shop he had established
in a remodeled nineteenth century coach house (Fig. 4). Charlie
Chong/ Fion Zhang
72. FIGURE 1. George Crampton, developer of the borescope
Charlie Chong/ Fion Zhang
73. FIGURE 2. Tests of forgings for a steam turbine generator
shaft manufactured in the 1920s FIGURE 3. Inspectors use early
borescopes to visually inspect piping at an Ohio oil refinery
Charlie Chong/ Fion Zhang
74. FIGURE 4. Periscope built in the 1940s is checked before
shipment to a Texas chemical plant Charlie Chong/ Fion Zhang
75. 2.1.4 Wartime Borescope Developments After World War II
began, Crampton devoted much of his energy to the war effort,
filling defense orders for borescopes (Fig. 5). Crampton practiced
medicine until noon, then went to the nearby workshop where he
visually tested the bores of 37 mm antiaircraft guns and other
weapons. During the war, borescopes were widely used for testing
warship steam turbines (particularly their rotating shafts). The
United States Army also used borescopes for inspecting the barrels
of tank and antiaircraft weapons produced in Philadelphia. An even
more challenging assignment lay ahead. The scientists working to
develop a successful nuclear chain reaction in the top secret
Manhattan Project asked Crampton to provide a borescope for
inspecting tubes near the radioactive pile at its guarded location
beneath the stadium seats at the University of Chicago's Stagg
Field. Crampton devised an aluminum borescope tube 35 mm (1.4 in.)
in diameter and 10 m (33 ft) long. The device consisted of 2 m (6
ft) sections of dual tubing joined by bronze couplings which also
carried an 8 V lighting circuit. Charlie Chong/ Fion Zhang
76. FIGURE 5. Using a borescope, an inspector at an automobile
plant during World War H checks the interiors of gun tubes for 90
mm antiaircraft guns Charlie Chong/ Fion Zhang
77. The inspector standing directly in front of the bore was
subject to radioactive emissions from the pile, so Crampton mounted
the borescope outside of a heavy concrete barrier. The operator
stood at a right angle to the borescope, looking through an
eyepiece and revolving the instrument manually. The borescope
contained a prism viewing head and had to be rotated constantly. It
was supported in a steel V trough resting on supports whose height
could be varied. Crampton also mounted a special photographic
camera on the eyepiece. The original Manhattan Project borescope
was later improved with nondarkening optics and a swivel-joint
eyepiece that permitted the operator to work from any angle (this
newer instrument did not require the V trough). It also was capable
of considerable bending to snake through the tubes in the reactor.
A total of three borescopes were supplied fbr this epochal project
and they are believed to be the first optical instruments to use
glass resistant to radioactivity. Charlie Chong/ Fion Zhang
78. Manhattan Project Charlie Chong/ Fion Zhang
79. Manhattan Project Charlie Chong/ Fion Zhang
80. Manhattan Project Charlie Chong/ Fion Zhang
81. 2.1.5 Borescopes and Aircraft Tests Aircraft inspection
soon became one of the most important uses of borescope technology.
In 1946, an ultraviolet light borescope was developed for
fluorescent testing of the interior of hollow steel propeller
blades. The 100 W viewing instniment revealed interior surface
discontinuities as glowing green lines. Later, in 1958, the entire
United States' B-47 bomber fleet was grounded because of metal
fatigue cracks resulting from low level simulated bombing missions.
Visual testing with borescopes proved to be the first step toward
resolving the problem. The program became known as Project
Milkbottle, a reference to the bottle shaped pin that was a primary
connection between the fuselage and wing (Fig. 6). In the late
1950s, a system was developed for automatic testing of helicopter
blades. The borescope, supported by a long bench, could test the
blades while the operator viewed results on a television screen
(Fig. 7). The system was used extensively during the Vietnam
conflict and helicopter manufacturers continue to use borescopes
for such critical tests. Charlie Chong/ Fion Zhang
82. FIGURE 6. Inspector using a borescope to check for metal
fatigue cracks in a B-47 bomber during grounding of the bomber
fleet in 1958 FIGURE 7. Visual testing of the frame of a 10 m (32
ft) long helicopter blade using a 10 m (32 ftj borescope; the
inspector could view magnified results on the television screen at
bottom left Charlie Chong/ Fion Zhang
83. After a half century of pioneering work, George Crampton
sold his borescope business to John Lang of Cheltenham,
Pennsylvania, in 1962.67 Lang had developed the radiation resistant
optics used in the Manhattan Project borescope, as well as a system
for keeping it functional in high temperature environments. He also
helped pioneer the use of closed circuit television with borescopes
for testing the inner surfaces of jet engines and wings, hollow
helicopter blades and nuclear reactors. In 1965, the company
received a patent on a borescope whose mirror could he very
precisely controlled. This borescope could zoom to high
magnification and could intensely illuminate the walls of a chamber
by means of a quartz incandescent lamp containing iodine vapor. The
basic design of the borescope has been in use for many decades and
it continues to develop, accommodating advances in video,
illumination, robotic and computer technologies. Charlie Chong/
Fion Zhang
84. 2.2.0 Certification of Visual Inspectors 2.2.1 Introduction
The recognition of the visual testing technique and the development
of formal procedures for educating and qualifying visual inspectors
were important milestones in the history of visual inspection.
Because visual testing can be performed without any intervening
apparatus, it was certainly one of the first forms of
nondestructive testing. In its early industrial applications,
visual tests were used simply to verify compliance to a drawing or
specification. This was basically a dimensional check. The
soundness of the object was determined by liquid penetrant,
magnetic particle, radiography or ultrasonic testing. Following
World War II, few inspection standards included visual testing. By
the early 1960s, visual tests were an accepted addition to the
American Welding Society's code hooks. In NAV SHIPS 250-1500-1, the
US Navy included visual tests with its specifications for other
nondestructive testing techniques for welds. Charlie Chong/ Fion
Zhang
85. By 1965, there were standards for testing, and criteria for
certifying the inspector had been established in five test methods:
liquid penetrant, magnetic particle, eddy current, radiographic and
ultrasonic testing. These five were cited in ASNT Recommended
Practice No. SNT-TC-1A, introduced in the late 1960s. The broad use
of visual testing hindered its addition to this group as a specific
method- there were too many different applications on too many test
objects to permit the use of specific acceptance criteria. It also
was reasoned that visual testing would occur as a natural result of
applying any other nondestructive test method. Charlie Chong/ Fion
Zhang
86. 2.2.2 Expanded Need for Visual Certification In the early
1970s, the need for certified visual inspectors began to increase.
Nuclear power construction was at a peak, visual certification was
becoming mandatory and nondestructive testing was being required.
In 1976, the American Society for Nondestructive Testing began
considering the need for certified visual inspectors. ASNT had
become a leading force in nondestructive testing and American
industry had accepted its ASNT Recommended Practice No. SNT-TC-IA
as a guide for certifying other NDT inspectors. In the spring of
1976, ASNT began surveying industry about their inspection needs
and their position on visual testing. Because of the many and
varied responses to the survey, a society task force was
established to analyze the survey data. In 1977, the task force
recommended that visual inspectors be certified and that visual
testing be made a supplement to ASNT Recommended Practice No.
SNT-TC-IA (1975). At this time, the American Welding Society
implemented a program that, following the US Navy, was the first to
certify inspectors whose sole function was visual weld testing.
Charlie Chong/ Fion Zhang
87. During 1978, ASNT subcommittees were formed for the eastern
and western halves of the United States. These groups verified the
need for both visual standards and trained, qualified and certified
inspectors. In 1980, a Visual Methods Committee was formed in
ASNT's Technical Council and the early meetings defined the scope
and purpose of visual testing (dimensional testing was excluded).
In 1984, the Visual Personnel Qualification Committee was formed in
ASNT's Education and Qualification Council. In 1986, a training
outline and a recommended reference list was finalized and the
Board of Directors approved incorporation of visual testing into
ASNT Recommended Practice No. SN T-TC -1 A. Charlie Chong/ Fion
Zhang
88. Part 3: VISION AND LIGHT 3.1 The Physiology of Sight 3.1.1
Visual Data Collection Human visual processing occurs in two steps.
First the entire field of vision is processed. This is typically an
automatic function of the brain, sometimes called pre-attentive
processing. Secondly, focus is localized to a specific object in
the processed field. Studies at the University of Pennsylvania
indicate that segregating specific items from the general field is
the foundation of the identification process. Based on this
concept, it is now theorized that various light patterns reaching
the eyes are simplified and encoded, as lines, spots, edges,
shadows, colors, orientations and referenced locations within the
entire field of view. The first step in the subsequent
identification process is the comparison of visual data with the
long-term memory of previously collected data. Some researchers
have suggested that this comparison procedure is a physiological
cause of deja vu, the uncanny feeling of having seen something
before. Charlie Chong/ Fion Zhang
89. The accumulated data are then processed through a series of
specific systems. Certain of our light sensors receive and respond
only to certain stimuli and transmit their data to particular areas
of the brain for translation. One kind of sensor accepts data on
lines and edges; other sensors process only directions of movement
or color. Processing of these data discriminates between different
complex views by analyzing their various components. By experiment
it has been shown that these areas of sensitivity have a kind of
persistence. This can be illustrated by staring at a lit candle,
then diverting the eyes toward a blank wall. For a short time, the
image of the candle is retained. The same persistence occurs with
motion detection and can he illustrated by staring at a moving
object, such as a waterfall, then at a stationary object like the
river bank. The bank will seem to flow because the visual memory of
motion is still present. Charlie Chong/ Fion Zhang
90. 3.1.2 Differentiation in the Field of View Boundary and
edge detection can be illustrated by the pattern changes in Fig. 8.
When scanning the figure from left to right, the block of reversed
Ls is difficult to separate from the upright Ts in the center but
the boundary between the normal Ts and the tilted Ts is easily
apparent. The difficulty in differentiation occurs because
horizontal and vertical lines comprise the L and upright T groups,
creating a similarity that the brain momentarily retains as the eye
moves from one group to the other. On the other hand, the tilted Ts
share no edge orientations with the upright Ts, making them stand
out in the figure. Differentiation of colors is more difficult when
the different colors are in similarly shaped objects in a pattern.
The recognition of geometric similarities tends to overpower the
difference in colors, even when colors are the object of interest.
Additionally, in a grouping of different shapes of unlike colors,
where no one form is dominant, a particular form may hide within
the varied field of view. However, if the particular form contains
a major color variance, it is very apparent. Experiments have shown
that such an object may be detected with as much ease from a field
of thirty as it is from a field of three. Charlie Chong/ Fion
Zhang
91. FIGURE 8. Pattern changes illustrating boundary and edge
detection Charlie Chong/ Fion Zhang
92. 3.1.3 Searching the Field of View The obstacles to
differentiation discussed above indicate that similar objects are
difficult to identify individually. During pre-attentive
processing, particular objects that share common properties such as
length, width, thickness or orientation are not different enough to
stand out. If the differences between a target object and the
general field is dramatic, then a visual inspector requires little
knowledge of what is to be identified. When the target object is
similar to the general field, the inspector needs more specific
detail about the target. In addition, the time required to detect a
target increases linearly with the number of similar objects in its
general field. When an unspecified target is being sought, the
entire field must be scrutinized. If the target is known, it has
been shown statistically that only about half of the field must be
searched. Charlie Chong/ Fion Zhang
93. The differences between a search for simple features and a
search for conjunctions or combinations of features can also have
implications in nondestructive testing environments. For example,
visual inspectors may be required to take more time to check a
manufactured component when the possible errors in manufacturing
are characterized by combinations of undesired properties. Less
time could be taken for a visual test if the manufacturing errors
always produced a change in a single property. Another aspect of
searching the field of view addresses the absence of features. The
presence of a feature is easier to locate than its absence. For
example, if a single letter 0 is introduced to a field of many Qs,
it is more difficult to detect than a single Q in a field of Os.
The same difficulty is apparent when searching for an open 0 in a
field of closed Os. In this case statistics show that the apparent
similarity in the target objects is greater and even more search
time is necessary Charlie Chong/ Fion Zhang
94. Experimentation in the area of visual search tasks
encompasses several tests of many 'individuals. Such experiments
start with studies of those features that should stand out readily,
displaying the basic elements of early vision recognition. The
experiments cover several categories, including quantitative
properties such as length or number. Also included are search tasks
concentrating on single lines, orientation, curves, simple forms
and ratios of sizes. All these tests verify that visual systems
respond more favorably to targets that have something added (Q
versus 0) rather than something missing. In addition, it has been
determined that the ability to distinguish differences in intensity
becomes more acute with a decreasing field intensity. This is the
basis of Weber's law. The features it addresses are those involved
in the early visual processes: color, size, contrast, orientation,
curvature, lines, borders, movement and stereoscopic depth. Charlie
Chong/ Fion Zhang
95. 3.2 Weber's Law 3.2.1 General Weber's law is widely used by
psychophysicists and entails the following tenets: (1) individual
elements such as points or lines are more important singly than
their relation to each other and (2) closed forms appear to stand
out more readily than open forms. To view a complete picture, the
visual system begins by encoding the basic properties that are
processed within the brain, including their spatial relationships.
Each item in a field of view is stored in a specific zone and is
withdrawn when required to form a complete picture. Occasionally,
these items are withdrawn and positioned in error. This malfunction
in the reassembly process allows the creation of optical illusions,
allowing a picture to be misinterpreted. Charlie Chong/ Fion
Zhang
96. The diagram in Fig. 9 represents a model of the early
stages of visual perception. The encoded properties are maintained
in their respective spatial relationships and compared to the
general area of vision. The focused attention selects and
integrates these properties, forming a specific area of
observation. In some cases, as the area changes, the various
elements comprising the observance are modified or updated to
represent present conditions. During this step, new data are
compared to the stored information. Charlie Chong/ Fion Zhang
97. FIGURE 9. Stages of visual perception Charlie Chong/ Fion
Zhang
98. Charlie Chong/ Fion Zhang
http://art.nmu.edu/cognates/ad175/background.html
99. 3.3. Vision Acuity 3.3.1 General Vision acuity encompasses
the ability to see and identify, what is seen. Two forms of vision
acuity are recognized and must be considered when attempting to
qualify visual ability. These are known as near vision and far
vision (acuity). Charlie Chong/ Fion Zhang
100. 3.3.2 Components of the Human Eye The components of the
human eye (Fig. 10) are often compared to those of a camera. The
lens is used to focus light rays reflected by an object in the
field of view. This results in the convergence of the rays on the
retina (film), located at the rear of the eyeball. The cornea
covers the eye and protects the lens. The quantity of light
admitted to the lens is controlled by the contraction of the iris
(aperture). The lens has the ability to become thicker or thinner,
which alters the magnification and the point of impingement of the
light rays, changing the focus. Eye muscles aid in the altering of
the lens shape as well as controlling the point of aim. This
configuration achieves the best and sharpest image for the entire
system. The retina consists of rod and cone nerve endings that lie
beneath the surface. They are in groups that represent specific
color sensitivities and pattern recognition sections. These areas
may be further subdivided into areas that collect data from lines,
edges, spots, positions or orientations. Charlie Chong/ Fion
Zhang
101. The light energy is received and converted to electrical
signals that are moved by way of the optic nerve system to the
brain where the data are processed. Because the light is being
reflected from an object in a particular color or combination of
colors, the individual wavelengths representing each hue also vary.
Each wavelength is focused at different depths within the retina,
stimulating specific groups of rods and cones (see Figs. 10 and
11). The color sensors are grouped in specific recognition patterns
as discussed above. Charlie Chong/ Fion Zhang
102. FIGURE 10. Components of the human eye in cross section
Charlie Chong/ Fion Zhang
103. FIGURE 11. Magnified cross section showing the blind spot
of the human eye Charlie Chong/ Fion Zhang
104. To ensure reliable observation, the eye must have all the
rays of light in focus on the retina. When the point of focus is
short or primarily near the inner surface of the retina closest to
the lens, a condition known as nearsightedness exists. If the focal
spot is deeper into the retina, farsightedness occurs. These
conditions are primarily the result of the eyeball changing from
nearly orb shaped to an elliptical or egg shape. In the case of the
nearsighted person, the long elliptical diameter is horizontal, If
the long diameter is in a vertical direction, farsightedness
occurs. These clinical conditions result from a very small shift of
the focal spot, on the order of micrometers (ten-thousandths of an
inch). Charlie Chong/ Fion Zhang
105. 3.3.3 Determining Vision Acuity The method normally used
to determine what the eye can see is based on the average of many
measurements. The average eye views a sharp image when the object
subtends an arc of five minutes, regardless of the distance the
object is from the eye. The variables in this feature are the
diameter of the eye lens at the time of observation and the
distance from the lens to the retina. When vision cannot he
normally varied to create sharp clear images, then corrective
lenses are required to make the adjustment. While the eye lens is
about 17 mm (0.7 in.) from the retina, the ideal eyeglass plane is
about 21 mm (0.8 in.) from the retina. Differences in facial
features must therefore be considered when fitting for eyeglasses.
Under various working conditions, the glass lenses may not stay at
their ideal location. This can cause slight variations when
evaluating minute details and such situations must be individually
corrected. For the majority of visual testing applications, near
vision acuity is required. Most visual inspections are performed
within arm's length and the inspector's vision should be examined
at 400 mm (15.5 in.) distance. Examinations for far vision are done
at distances of 6 m (20 ft). Charlie Chong/ Fion Zhang
106. Keywords: The average eye views a sharp image when the
object subtends an arc of five minutes, regardless of the distance
the object is from the eye. For the majority of visual testing
applications, near vision acuity is required. Near vision should be
examined at 400 mm (15.5 in.) distance. Far vision are done at
distances of 6 m (20 ft). Charlie Chong/ Fion Zhang
107. 3.4 Vision Acuity Examinations 3.4.1 General Visual
testing may occur once or more during the fabrication or
manufacturing cycle to ensure product reliability. For critical
products, visual testing may require qualified and certified
personnel. Certification of the visual test itself may also be
required to document the condition of the material at the time of
testing. In such cases, testing personnel are required to
successfully complete vision acuity examinations covering specific
areas necessary to ensure product acceptability. For certain
critical inspections, it may be required for the eyes of the
inspector to be examined as often as twice per year. Charlie Chong/
Fion Zhang
108. 3.4.2 Near Vision Examinations The examination distance
should be 400 mm (16 in.) from the eyeglasses or from the eye
plane, for tests without glasses. When reading charts are used,
they should he in the vertical plane at a height where the eye is
on the horizontal plane of the center of the chart. Each eye should
be tested independently while the unexamined eye is shielded from
reading the chart but not shut off from ambient light. The Jaeger"
eye chart is widely used in the United States for near vision
acuity examinations. The chart is a 125 X 200 mm (5 x 8 in.)
off-white or grayish card with an English language text arranged
into groups of gradually increasing size. Each group is a few lines
long and the lettering is black. In a vision examination using this
chart, visual testing personnel may be required to read, for
example, the smallest letters at a distance of 300 mm (12 in.).
Near vision acuity examinations that are more clinically precise
are described below. Charlie Chong/ Fion Zhang
109. 3.4.3 Far Vision Examinations Conditions are the same as
those for near vision examinations, except that the chart is placed
6 m (20 ft) from the eye plane. Again, each eye is tested
independently. Charlie Chong/ Fion Zhang
110. 3.4.4 Grading Vision Acuity The criterion for grading
vision acuity is the ability to see and correctly identify 7 of 10
optotypes of a specific size at a specific distance. The average
individual should be able to read six words in four to five
seconds, regardless of the letter size being viewed. The
administration of a vision acuity examination does not necessarily
require medical personnel, provided the administrator has been
trained and qualified to standard and approved methods. In some
instances specifications may require the use of medically approved
personnel. In these cases, the administrator of the examination may
be trained by medically approved personnel for this application. In
no instance should any of these administrators try to evaluate the
examinations. Charlie Chong/ Fion Zhang
111. If an applicant does not pass the examination (fails to
give the minimum number of correct answers required by
specification), the administrator should advise the applicant to
seek a professional examination. If the professional responds with
corrective lenses or a written evaluation stating the applicant can
and does meet the minimum standards, the applicant may be
considered acceptable for performance of the job. Charlie Chong/
Fion Zhang
112. An eye chart is a chart used to measure visual acuity.
Types of eye charts include the logMAR chart, Snellen chart,
Landolt C, Lea test and the Jaeger chart. Procedure Charts usually
display several rows of optotypes (test symbols), each row in a
different size. An optotype is a standardized symbol for testing
vision. Optotypes can be specially shaped letters, numbers, or
geometric symbols. The person is asked to identify the optotype on
the chart, usually starting with large rows and continuing to
smaller rows until the optotypes cannot be reliably identified
anymore. Technically speaking, testing visual acuity with an eye
chart is a psychophysical measurement that attempts to determine a
sensory threshold (see also psychometric function). Charlie Chong/
Fion Zhang
113. Ototype Charlie Chong/ Fion Zhang
114. Snellen Chart- Far Vision Acuity Charlie Chong/ Fion
Zhang
115. Golovin-Sivtsev Table Charlie Chong/ Fion Zhang
116. Jaeger chart Charlie Chong/ Fion Zhang
117. 3.4.5 Vision Acuity Examination Requirements There are
some basic requirements to be followed when setting up a vision
acuity examination system. The distances mentioned above are
examples but there are also detailed requirements for the vision
chart. The chart should consist of a white matte finish with black
characters or letters. The background should extend at least the
width of one character beyond any line of characters. Sloan letters
as shown in Fig. 12 were designed to be used where letters must be
easily recognizable. Each character occupies a five stroke by five
stroke space. Charlie Chong/ Fion Zhang
118. FIGURE 12. Letters used for acuity examination charts
(measurements in stroke units) Charlie Chong/ Fion Zhang
119. The background luminance of the chart should be 85 5 cdm-
2. The luminance is a reading of the light reflected from the white
matte finish toward the reader. When projected images are used, the
parameters for the size of the characters, the background luminance
and the contrast ratio are the same as those specified for charts.
In no case should the contrast or illumination of the projected
image be changed. A projection lamp of appropriate wattage should
be used. When projecting the image, room lighting is subdued. This
should not cause any change in the luminance of the projected
background contrast ratio to that of the characters. The room
lighting for examinations using charts should be 800 lx (75 ftc).
Incandescent lighting of the chart is recommended to bring the
background luminance up to 85 5 cdm- 2. Fluorescent lighting should
not be used for vision acuity examinations. Incandescent lamps emit
more light in the yellow portion of the visible spectrum. This
makes reading more comfortable for the examinee. Fluorescent lamps,
especially those listed as full spectrum, are good for color vision
examinations. Charlie Chong/ Fion Zhang
120. Many of the lighting conditions for vision acuity
examinations can be met by using professional examination units.
With one such piece of equipment, the examinee views slides under
controlled, ideal light conditions. Another common design is used
both in industrial and medical examinations. With this unit, the
individual looks into an ocular system and attempts to identify
numbers, letters or geometric differences noted in illuminated
slides. The examinee is isolated from ambient light. The slides and
their respective data were developed by the Occupational Research
Center at Purdue University, based on many individuals tested in
many different occupations. Categories were developed for different
vocations and are provided as guides for examinations required by
various industries. Such equipment is expensive and accordingly eye
charts are still very popular. Table 1 compares the results of
these three vision acuity examination systems. Charlie Chong/ Fion
Zhang
121. TABLE 1. Eye examination system conversion chart Charlie
Chong/ Fion Zhang
122. There are slight differences between the reading charts
and the slides. The reading chart distance for one popular letter
card is 400 mm (16 in.). The simple slide viewer is set for near
vision testing at 330 min (13 in.). There also are some differences
between individual examination charts. Most of the differences are
the result of variances in typeface, ink and the paper's ink
absorption rate. Regardless of the examination system that is used,
the requirements for the lighting and contrast remain the same.
Charlie Chong/ Fion Zhang
123. 3.5 Visual Angle 3.5.1 Posture Posture affects the manner
in which an object is observedappropriate posture and viewing angle
are needed to minimize fatigue, eyestrain and distraction. The
viewer should maintain a posture that makes it easy to maintain the
optimum view on the axis of the lens. 3.5.2 Peripheral Vision Eye
muscles may manipulate the eye to align the image on the lens axis.
The image is not the same unless it impinges on the same set of
sensors in the retina (see Fig. 13). As noted above, different
banks of sensors basically require different stimuli to perform
their functions with optimum results. Also, light rays entering the
lens at angles not parallel to the lens axis are refracted to a
greater degree. This changes the quality and quantity of the light
energy reaching the retina. Even the color and contrast ratios vary
and depth perception is altered Charlie Chong/ Fion Zhang
124. FIGURE 13. Vision acuity of peripheral vision Charlie
Chong/ Fion Zhang
125. The commonly quoted optimum, included angle of five (5)
minutes of arc is the average in which an individual encloses a
sharp image. There are other angles to be considered when
discussing visual testing. The angle of peripheral vision is not a
primary consideration when performing detailed visual tests. It is
of value under certain inspection conditions: (1) when surveying
large areas for a discontinuity indication that (2) has a high
contrast ratio with the background and (3) is observed to one side
of the normal lens axis. The inspector's attention is drawn to this
area and it can then he scrutinized by focusing the eyes on the
normal plane of the lens axis. Charlie Chong/ Fion Zhang
126. 3.5.3 Visual Testing Viewing Angle The angle of view is
very important during visual testing. The viewer should in all
cases attempt to observe the target on the center axis of the eye.
The angle of view should not vary more than 45 degrees from normal.
Figure 14 shows how the eye perceives an object from several angles
and how the object appears to change or move with a change in
viewing angle. Charlie Chong/ Fion Zhang
127. FIGURE 14. Shifting eye positions change apparent object
size and location Charlie Chong/ Fion Zhang
128. The same principle applies to objects being viewed through
accessories such as mirrors or borescopes. The field of view should
be maintained much in the same way that it is when viewed directly.
On reflective backgrounds, the viewing angle should be off normal
but not beyond 45 degrees. This is done so that the light reflected
off the surface is not directed toward the eyes, reducing the
contrast image of the surface itself. It also allows the evaluation
of discontinuities without distorting their size, color or
location. This is very important when using optical devices to view
areas not available to direct line of sight. Charlie Chong/ Fion
Zhang
129. 3.6 Color Vision 3.6.1 General There are specific
industries where accuracy of color vision is important: paint,
fabrics and photographic film are examples. Surface inspections
such as those made during metal finishing and in rolling mills are
to determine manufacturing discontinuities. Color changes are not
indicative of such discontinuities and therefore, for practical
purposes, color is not as significant in these applications.
However, heat tints are sometimes important and colors may be
crucial in metallography and failure analysis. When white light
testing is performed, it must be remembered that white light is
composed of all the colors (wavelengths) in the spectrum. If the
inspector has color vision deficiencies, then the test object is
being viewed differently than when viewed by an inspector with
normal color vision. Color deficiency may be as critical as the
test itself. During visual testing of a white or near white object,
slight deficiencies in color vision may be unimportant. During
visual testing of black or near black objects, color vision
deficiencies make the test object appear darker Charlie Chong/ Fion
Zhang
130. 3.6.2 Color Vision Examinations Ten percent of the male
population have some form of color vision deficiency. The so-called
color blind condition affects even fewer people truly color blind
individuals are unable to distinguish red and green. But, there are
many variations and levels of sensitivity between individuals with
normal vision and those with color deficiencies. There are two
causes of color deficiency: inherited and acquired. And each of
these may be subdivided into specific medical problems. Most such
subdivisions are typically discovered during the first vision
examination. The most common color deficiencies are hereditary and
occur in the red-green range. About 0.5 percent of the affected
individuals are female, in the red-green range. Women constitute
about 50 percent of those affected in the blue-yellow range. Most
such deficiencies occur in both eyes and in rare instances in only
one eye. About 0.001 percent of the affected groups in the
hereditary portion have their deficiency in the blue-green range.
Individuals in the red green group may make misinterpretations of
discontinuities in shades of red, browli, olive and gold. Charlie
Chong/ Fion Zhang
131. Color Vision Examinations-Ishihara Plates Charlie Chong/
Fion Zhang
132. Color Vision Examinations-Ishihara Plates Charlie Chong/
Fion Zhang
http://www.nature.com/nmeth/journal/v8/n6/full/nmeth.1618.html
133. Color Vision Examinations-Ishihara Plates Charlie Chong/
Fion Zhang
http://www.today.com/health/surprise-side-effect-new-specs-may-fix-color-blindness-1C8487550
134. Acquired color deficiency is a greater problem to good
color vision testing. The acquired deficiencies may affect only one
eye and a change from acceptable color vision to a recognizable
problem may he very gradual. Various medical conditions can cause
such a change to occur (Table 2 lists conditions that produce color
vision deficiencies in particular color ranges). Most acquired
color vision problems vary in severity and may be associated with
ocular pathology. If the disease continues for an extended period
of time without treatment, the deficiencies may become erratic in
intensity and may vary from the red-green or blue-yellow ranges.
Aging can also affect color vision. Charlie Chong/ Fion Zhang
135. TABLE 2. Causes of acquired color vision deficiencies
Color Vision Deficiency Cause of Deficiency Blue-yellow deficiency
Glaucoma Myopic retinal degeneration Retinal detachment Pigmentary
degeneration of the retina (including retinitis pigmentosa) Senile
macular degeneration Chorioretinitis Retinal vascular occlusion
Diabetic retinopathy Hypertensive retinopathy Papilledema Methyl
alcohol poisoning Central serous retinopathy (accompanied by
luminosity loss in red) Charlie Chong/ Fion Zhang
136. TABLE 2. Causes of acquired color vision deficiencies
Color Vision Deficiency Cause of Deficiency Red-green deficiency
Optic neuritis (including retrobulbar neuritis) Tobacco or toxic
amblyopia Leber's optic atrophy Lesions of the optic nerve and
pathway Papillitis Hereditary juvenile macular degeneration
{Stargardt's and Best's disease) Blue-yellow deficiency Dominant
hereditary optic atrophy Red-green or blue-yellow deficiency
Juvenile macular degeneration Charlie Chong/ Fion Zhang
137. 3.6.3 Color Vision Classifications Two functions that
determine an individual's sensation range are their color
perception and color discrimination. When a primary color is
mistaken for another primary color, this is an error in perception.
An error in discrimination is an error of lesser magnitude
involving a mistake in hue selection. During a vision examination,
these two functions are tested independently. A color vision
examination performed with an anomaloscope allows the mixing of red
and green lights to match a yellow light standard. Yellow and blue
lights may be mixed to match a white light. An individual with
normal vision requires red, blue and green light to mix and match
colors of the entire color spectrum. A color deficient person may
require fewer than the three lights to satisfy the color sensation.
Table 3 indicates the type of deficiencies and the percent of the
male population known to be affected Charlie Chong/ Fion Zhang
138. Anomaloscope Charlie Chong/ Fion Zhang
139. Anomaloscope Test Charlie Chong/ Fion Zhang
140. TABLE 3. Classification of color vision deficiencies and
percent of affected males Color Vision Hereditary deficiencies
trichromatism three colors: red, green. blue) normal vision
anomalous (defective) dichromatism (two colors)* protanopia (red
lacking) deureranopia (green lacking) trianopia {blue lacking)
tetratanopia (yellow lacking) Acquired deficiencies tritan (blue
yellow) protan-deutan (red-yellow) Charlie Chong/ Fion Zhang
Percent Males Affected 92 6 or 7 11 rare very rare data not
available data not available *Deficiency most often referenced when
discussing color blindness
141. TABLE 4. Naval Submarine Medical Research Laboratory color
vision classification system Class Description 0 Normal I Mild
anomalous trichromat ll Unclassified anomalous trichromat (includes
mild and moderate classes) III Moderate anomalous trichromat IV
Severely color deficient {includes severe anomalous trichromats,
dichromats andmonochromats) Charlie Chong/ Fion Zhang
142. For the practical purpose of classifying personnel
affected by hereditary color deficiencies, the Naval Submarine
Medical Research Laboratory has developed the classifications shown
in Table 4. about 50 percent of color deficient people can be
categorized in accordance with this table. Class I covers 30
percent of the color deficient population and Class III accounts
for 20 percent. Individuals in Class I can judge colors used as
standards for signaling, communication and identification as fast
and as accurately as zero class persons can. The limitation of
Class I people is when good color discrimination is necessary.
Persons in Class III may be used in other areas such as radio
repair, chemistry, medicine and surgery, electrical manufacturing
or general painting. Class II encompasses staff members, managers
or clerical help, whose need for color resolution is not critical.
Individuals in Class IV must be restricted from occupations where
color differentiation of any magnitude is required. Charlie Chong/
Fion Zhang
143. As with vision acuity examinations, there are many
different examinations for color vision. Color vision is often
tested with pseudoisochromatic plates or cards on which the
detection of certain figures depends on red-green discrimination.
Unfortunately, most common vision acuity examinations were designed
to identify hereditary red-green deficiencies and ignore
blue-yellow deficiencies. A good, discriminating examination
technique is illustrated in color Plates 1 to 7. The diagrams show
the sequence in which the colors are arranged in each photograph
for each deficiency, differing from the sequence according to
normal vision illustrated in Plate 1. 21 (Caution: These plates are
provided for educational purposes only. Photography, print
reproduction and chemical changes all cause colors to vary from the
original and fade with time. Under no circumstances should
illustrations in this book be used for vision examinations.)
Charlie Chong/ Fion Zhang
144. Pseudoisochromatic plates
http://www.healthytimesblog.com/2011/04/facts-about-color-blindness/
Charlie Chong/ Fion Zhang
145. Charlie Chong/ Fion Zhang
http://www.healthytimesblog.com/2011/04/facts-about-color-blindness/
146. The exam consists of the examinee's arranging fifteen
colored caps into a circle according to changes in hue progressing
from a reference cap. To help evaluate the outcome, each cap is
numbered on the back. A perfect score has the caps in numerical
sequence. This test is used for those known to have a color vision
deficiency. The test allows for the evaluation of the individual's
ability and determines the specific area of the deficiency. The
arrangement of colors allows confusion to exist across the
quadrants of the circle. For instance, reds can be confused with
blue-greens. One authority has stated that anyone who can pass this
test should have no problem in any work requiring color vision
acuity. Two types of red-green deficient patterns can be noted.
Charlie Chong/ Fion Zhang
147. Individuals in these categories confuse green (4) with
redpurple (13) and blue-green (3) with red (12). The sequence then
appears as 4, 13, 3 and 12. Persons with the blue-yellow deficiency
confuse yellow-green (7) with purple (15), creating a sequence of
7, 15, 8, 14 and 9. As in the normal vision acuity examinations,
lighting requirements and time must be controlled for color vision
examinations. The illumination intensity of full spectrum
fluorescent lighting should be no less than 200 lx (20 ftc). The
rating of the light source is known as the color temperature. A low
color temperature lamp such as an incandescent lamp makes it easier
for persons with borderline color deficiencies to guess the colors
correctly. A color temperature of 6,700 K is preferred. Too high a
color temperature increases the number of reading errors. To
eliminate glare, the light source should be 45 degrees to the
surface while the patient is perpendicular to it. The reading
distance should be about 400 to 600 mm (15 to 24 in.) or arm's
length. Charlie Chong/ Fion Zhang
148. To perform such an examination, two minutes should be
allotted to arrange all fifteen caps in their appropriate
positions. In summary, color deficiency can be acquired or
inherited. Some color deficiencies may be treated, alleviated or
minimized. Pseudoisochromatic plates in conjunction with the
progressive hue color caps provide an adequate test for most
industrial visual inspectors. Full spectrum lighting (6,700 K) is
necessary for accurate test results. It should be added that,
because the visible spectrum is made up of colors of varying
wavelengths and the black and white colors consist of various
combinations of colors, deficiencies in any part of the color
spectrum has an impact on certain black and white inspection
methods, including X-ray film review It is recommended that all
nondestructive testing personnel have their color vision tested
annually, while taking their vision acuity examination. Charlie
Chong/ Fion Zhang
149. Caps for Color Vision Examinations The exam consists of
the examinee's arranging fifteen colored caps into a circle by a
change in hue progressing from a reference cap. To help evaluate
the outcome, each cap is numbered on the