Light Guide TechniquesUsing LED LampsApplication Brief I-003

What Is a Light Guide?A light guide is a device designedto transport light from a lightsource to a point at some distancewith minimal loss. Light is trans-mitted through a light guide bymeans of total internal reflection.Light guides are usually made ofoptical grade materials such asacrylic resin, polycarbonate,epoxies, and glass. A light guidecan be used to transmit light froman LED lamp on a pc board to afront panel for use as statusindication, can be used to collectand direct light to backlight anLCD display or legend, and can beused as the means to illuminate agrid pattern on a see throughwindow. This Application Briefdiscusses the basics of simple lightguide design for these and otherpossible uses.

Basic PrinciplesSnells Law: When light rays areincident to a boundary betweentwo mediums, i.e. plastic and air,the light rays are refracted whenthey cross the boundary asillustrated in Figure 1. The angle atwhich the light rays are incident tothe boundary is called the angle ofincidence, i, and the angle atwhich the light rays leave theboundary is called the angle of

Figure 1. Refracted Light Ray.

refraction, f,. Snells law states:the index of refraction of the firstmedium, ni, multiplied by thesine of the angle of incidence atthe boundary, i, is equal to theindex of refraction of the secondmedium, nr, multiplied by thesine of the angle of refraction atthe boundary, f.

Specular Reflection: Specularreflection is defined when theangle of incidence equals the angleof reflection as shown in Figure 2.Specular reflected light rays arereflected without loss.

Fresnel Loss: When light rayscross the boundary from onemedium to another, there is a lossdue to reflection at the boundaryas shown in Figure 2. This is calledFresnel loss and is calculated withthe following expression:

(2)

When light rays cross a boundaryinto a more dense medium, theangle f is less than the angle i.Conversely, when light rays crossa boundary into a less densemedium, the angle f is greaterthan the angle i. This is illustratedin Figure 3 for light rays passingthrough a parallel plastic (glass)plate. The light rays are incidentto the plate top surface at an anglei, are refracted within the plate atthe angle f, are incident to the

For plastic to air and glass to airinterface boundaries, the Fresnelloss is 4%.

for plastic (glass) to air interfaces.

i

f

ni

nr

INCIDENCEMEDIUM

MEDIABOUNDARY

REFRACTIONMEDIUM

REFRACTEDLIGHT RAY

INCIDENTLIGHT RAY

Snells Law = ni sini = nf sinf (1)

ni nf ni + nf

Fresnel Loss = 100 2

1.50 - 1.001.50 + 1.00

Fresnel Loss = 1002

= 4%

plate bottom surface of the plate atthe angle 'i, and then are refractedin the air at the angle 'f. The angleof refraction within the plasticplate f is smaller than the angle ofrefraction in air 'f since the plasticis a more dense medium than air.The exit rays are parallel to theincident rays because the internalangle of refraction f and theinternal angle of incidence 'i areequal, and because the externalangle of incidence i and theexternal angle of refraction 'f areequal.

Total Internal Reflection: Whenthe angle of refraction is 90 theincident light ray is refracted alongthe boundary, as shown in Figure4. The sin f (90) = 1.0, andEquation 1 for Snells law reducesto: ni sin i = nf. This expressioncan be rewritten to define thecritical incident angle for totalinternal reflection, c:

Critical Angle Definition:

sin c = (3)

Setting nf = 1.0 in Equation 3, theindex of refraction value for air,the critical angle for a light guidecan be quickly determined whenthe material index of refraction isknown. For most plastics andglass, the index of refraction isapproximately 1.50. Thus, thecritical angle for total internalreflection for most light guidematerials is approximately 42.Internal specular reflection withina light guide at the guide surface toair boundary is utilized to helptransmit light through the lightguide.

Figure 2. Specular Reflected Light Ray at Mirror Smooth Boundary.

Figure 3. Light Ray Passing Through Nondiffused Plastic (Glass) Parallel Plate.

Figure 4. Definition of Critical Angle for Total Internal Reflection.

nfni

i r

f

ni

nr

INCIDENCEMEDIUM

SMOOTH SPECULARREFLECTINGBOUNDARY

REFRACTEDLIGHT RAY

INCIDENTLIGHT RAY

SPECULARREFLECTEDLIGHT RAY

REFLECTION MEDIUMMORE DENSE THANINCIDENCE MEDIUM

i = rf < i

i

i'

r

r'

f

f'

AIR

AIR

i = r = 4% FRESNEL LOSSi' = r' = 4% FRESNEL LOSSf = i'i = f' = EXIT RAY OFFSET AND

PARALLEL TO INCIDENT RAY

INCIDENT RAY

NON-DIFFUSEDPLASTIC (GLASS)PLATE

SPECULAR REFLECTINGSMOOTH SURFACE

SPECULAR REFLECTINGSMOOTH SURFACE

EXIT RAY = 92%OF INCIDENT RAY

c = CRITICAL ANGLEi < c FOR EXIT LIGHT RAYi' > c FOR TOTAL INTERNAL REFLECTION

f

c i'

i

f = 90LIGHT RAY REFRACTEDALONG BOUNDARY

TOTAL INTERNALLYREFLECTED LIGHT RAY

INCIDENT LIGHT RAYS

EXIT LIGHT RAY

nf ni

c = 42 approximate value forplastics and glass.

sin c = = 0.667,1.50

1.0

2

Light rays internal to a light guideincident to guide surface to airboundary are total internallyreflected when the angle ofincidence is 42 or greater. Havingthe critical angle being slightly lessthan 45 for most light guidematerials is very convenientbecause it allows the use of 45reflecting prism surfaces in lightguide designs.

Ray Tracing: Ray tracing is atechnique used to predict the pathof light rays into, through, and outof a light guide. The principles ofSnells law, Fresnel loss, andspecular reflection are applied ateach guide surface to air interfaceto determine the direction of thelight ray. Ray tracing is used in thisApplication Brief to illustrate theperformance of light guide designs.

Light Guide DesignThere are three design issues to beexamined when designing a lightguide:1) effective flux coupling to get the

light from an LED lamp into thelight guide with minimal loss,

2) transmitting the light throughthe guide to the exit surface, and

3) allowing the light to escapethrough the exit surface withminimal loss.

Flux Coupling to Get LED Lightinto a Light Guide: Flux from anLED lamp must be effectivelycoupled to the entrance end of alight guide to permit light capture(light to enter the light guide) withminimal loss before it can beeffectively transmitted and utilized.Flux coupling and capture areusually ineffective when the LEDlamp is external to the envelope ofthe light guide surface to airboundary, and conversely areeffective when the lamp is located

inside the light guide surface to airboundary.

With the LED lamp external to thelight guide, as shown in Figure 5,effective flux coupling and lightcapture occur only when the LEDlamp radiation pattern anglematches the acceptance patternangle of the light guide. Thus,effective flux coupling may be verydifficult to accomplish and most ofthe flux from the LED lamp may belost. Less than 10% of the availableflux is typically captured by a lightguide with this configuration.

A lens may be used for fluxcoupling to focus the flux from anLED lamp onto the entrance end ofa light guide, as shown in Figure 6.The focused flux should just fillthe entrance end of the light guide.Light capture can be up to 80%

effective, but does require avail-ability of physical distance toaccommodate the focal length ofthe lens. The cost of the focusinglens must be added to the cost ofthe light pipe design.

The best design for most effectiveflux coupling is to have the LEDlamp located inside the envelope ofthe light guide surface to airboundary. This concept is illus-trated in Figure 7a. In this configu-ration, the LED lamp is embeddedinto the light guide and all lightrays emanating from the LED lampare captured by the light guide. Thelight capture effectiveness is 92%,taking into account the Fresnellosses across the air gap. Thisdesign concept is recommendedfor use with dome LED packagedevices such as T-1 3/4, T-1, andsubminiature LED lamps.

LOST FL

UX

LOST FLUX

LIGHT GUIDE

LESS THAN 10% FLUX CAPTURE

LED LAMP

e a

Figure 5. LED Lamp External to Light Guide.

Figure 6. Using a Lens to Focus LED Light Onto Light Guide.

LIGHT GUIDE

UP TO 80% FLUX CAPTUREFLUX FOCUSING LENS

LED LAMPe

f f

3

When the LED lamp package isglued into the light guide with anoptical grade epoxy, as shown inFigure 7b, the epoxy package ofthe lamp optically disappears dueto the elimination of Fresnellosses, and the flux capture isessentially 100%. In most lightguide applications, using epoxy toglue the LED lamp to the lightguide to eliminate air gap Fresnelloss is neither practical nornecessary. All of the suggestedlight guide designs presented inthis Application Brief assume thereis an air gap between the LEDlamp and the light guide.

Physical Attributes of a LightGuide: The exterior surfacefinishes of a light guide are impor-tant to assure proper operation, asshown in Figure 8. The sidesparallel to the direction of lighttravel should be smooth, like amirror, to affect total internalreflection. They may be paintedwith a white light reflecting paintto reflect those diagonal rays lessthan the critical angle that mayotherwise escape. The entranceend should be smooth, contoured

LIGHT GUIDE

8% FRESNEL LOSSIN AIR GAP

92% FLUX CAPTURE

LED LAMP

LIGHT GUIDE

LED EMITTER EPOXIED INTOLIGHT GUIDE TO ELIMINATE AIR GAP = NO FRESNEL LOSS

100% FLUX CAPTURE

LED LAMP

Figure 7a. LED Lamp Located Inside a Light Guide for Best Flux Coupling.

Figure 7b. LED Lamp Epoxied into a Light Guide to Eliminate Fresnel Loss.

SMOOTH FLAT OR CONCAVECONTOURED SURFACE TOMATCH LED LAMP

LIGHT GUIDE

DIFFUSED EXITSURFACE

ROUNDED CORNERS0.5 mm (0.020 IN.)MINIMUM RADIUS

SMOOTH (MIRROR)EXTERIOR SURFACE

OPTIONAL WHITE LIGHTREFLECTING PAINT

ON EXTERIOR SURFACE

to match the LED lamp device foreffective light capture, allowinglight rays to enter the light guidewith minimal reflection andscatter. The exit end should bediffused. A diffused exit end hasrandom critical angles acrossits surface providing a highprobability light rays can escape,and also scatters the light raysproducing a wide radiation pat-tern.

Light guides may be made in anydesired shape, cylindrical (oval),

rectangular (square), conical(increasing in size from entranceend to exit end), or any specialshape (arrow, star shaped, quartermoon, etc.). For rectangular andspecial shapes, the corners shouldhave a radius greater than 0.5 mm(0.020 in.), not sharp, to assureillumination in the corners. Theshape of the light guide maygradually change along its length,i.e. from circular at the entranceend to accommodate the lamp, tosquare at the exit end, as shown inFigure 8.

Light Entrance End of LightGuides for Various Types ofLED Devices: For effective fluxcoupling and light capture, the lightentrance end of a light guideshould be smooth and flat orconcave contoured to match thelight output radiation pattern andpackage configuration of themating LED lamp device.

For SMT LED lamp devices thathave a light emitting area that is aflat surface, the entrance end of thelight guide should be a smooth flatsurface. The entrance end of thelight guide should be placed overand in close proximity to the lightemitting surface of the SMT LEDlamp for effective flux coupling

Figure 8. The Basic Attributes of a Light Guide, shown with a change in shapefrom Circular to Rectangular along its Length.

4

Figure 9. Light Guide with a SmoothFlat Entrance End positioned over anSMT LED Lamp.

Figure 10. A Light Guide with a Smooth Concave Entrance End increases FluxCoupling and Light Capture from an SMT Chip LED Lamp.

and light capture, as illustrated inFigure 9. The entrance end of thelight guide needs to be slightlylarger than the emitting surface ofthe LED lamp to assure 92% fluxcapture, taking into account theFresnel losses across the air gap.

LIGHT GUIDE

SMT LED LAMP

PC BOARD

SMOOTH, FLATSURFACE

ENTRANCEEND

SMT CHIP LED

PC BOARD

SMOOTH, CONCAVESURFACE INCREASES

FLUX CAPTURE

LIGHT GUIDE

20%-30% LOST FLUX

62%-72% FLUX CAPTURE

SMT Chip LED lamp packages arecubic in shape, diffused, allowinglight to emit from the sides as wellas the top. Only about 40% of thetotal available flux is emitted fromthe top. The other 60% is emittedfrom the side. Thus, only 40% ofthe light from an SMT Chip LEDlamp would be captured by a lightguide with a flat surface entranceend, the remaining flux is lost. Alight guide with a smooth concaveentrance end to fit over the SMTChip LED lamp is effective inincreasing flux capture, as shownin Figure 10. The smooth concavesurface enhances flux couplingand light capture by reducing thepossibility of a light ray intersect-ing the light guide at the criticalangle and being reflected. With theconcave entrance end, about 70%to 80% of the available emitted fluxfrom an SMT Chip LED is capturedby the light guide, and the lightloss is reduced to 20% to 30%.

This concave contoured entranceend technique may be used withany light guide/LED lamp combina-tion to enhance flux coupling and

light capture. In Figure 11, a Yokelead SMT subminiature lamp isused to illuminate a light guidelocated at the back side of a pcboard. The lamp is located in athrough hole and surface mountedon the component side of theboard. The smooth concavesurface entrance end of the lightguide captures more of the radi-ated flux from the LED lamp thandoes a flat surface.

Figure 11. The Concave End of a LightGuide Enhances Flux Coupling andLight Capture From an InvertedSurface Mounted Yoke Lead SMTSubminiature LED Lamp.

As a minimum insertion distancefor positive flux coupling and lightcapture, standard T-1 3/4 untinted,nondiffused LED lamps should beinserted into the entrance end of alight guide up to the LED reflectorcup, located within the lamppackage, as shown in Figure 12.This assures 92% flux capture,taking into account the Fresnelloss across the air gap between thelamp dome and light guide. Forbest performance, insertion to thebase flange on the lamp package isrecommended. For T-1 3/4 LED

CONCAVE SMOOTHSURFACE ENHANCES

FLUX CAPTURE

YOKE LEAD SMTSUBMINIATURE LED LAMP

PC BOARD

LIGHT GUIDE

5

lamps, the lamp acceptance holeshould be 5.33 mm (0.210 in.) to5.59 mm (0.220 in.) in diameter.The end of the hole should be asmooth spherical dome radius. Thehole should be at least 5.33mm (0.210 in.) in depth for mini-mum length insertion, and 8.31 mm(0.327 in.) minimum in depth forfull length insertion. For T-1 LEDlamps, the lamp acceptance holediameter should be 3.30 mm (0.130in.) to 3.43 mm (0.135 in.) indiameter. Only full length insertionto the lamp base flange is recom-mended for T-1 lamps to achieveeffective flux coupling and cap-ture, with a minimum hole depth of2.165 mm (0.085 in.).

LED light bars may also be used aslight sources for light guides.These devices that have a lightemitting area that is a large flatsurface. Therefore, for effectiveflux coupling and light capture theentrance end of the light guideshould be a smooth flat surface,placed over and in close proximityto the light emitting surface ofthe LED light bar, as illustrated inFigure 13. The entrance end of the

Figure 12. Insertion of T-1 3/4 and T-1 Untinted, Nondiffused LED Lampsinto the Entrance End of a Light Guide for Effective Flux Coupling.

PC BOARD

5727-13 AB I-003

92% FLUX CAPTURE

LIGHT GUIDE

SMOOTH, FLATSURFACE

ENTRANCE END

LEDLIGHT BAR

light guide needs to be slightlylarger than the emitting surface ofthe light bar to assure 92% fluxcapture, taking into account theFresnel losses across the air gap.

Diffused Exit End of a LightGuide: A diffused exit end pre-sents random critical angles tointernal light rays, assuring theprobability of light escaping from a

light guide. This may also beviewed as the diffused exit endhaving random indices of refrac-tion. The exiting light rays aredisbursed at random angles into awide radiation pattern of light, asshown in Figure 14.

Figure 13. Light Guide with a Smooth Flat Entrance End Positioned Over an LEDLight Bar for Best Flux Coupling.

LIGHT GUIDELIGHT GUIDE

92% FLUX CAPTURE

SMOOTH INTERIORSURFACE FOR LED

LAMP AT ENTRANCE END

T-1 3/4, T-1 LED LAMPT-1 3/4 LED LAMP

RECOMMENDED INSERTIONOF LAMP TO FLANGE ATBASE OF LAMP PACKAGE

MINIMUM INSERTIONFOR T-1 3/4 LAMP TOLED REFLECTOR CUP

6

Figure 14. Diffused Exit End Enhances the Probability of Light Escaping from aLight Guide.

LIGHT GUIDE

LIGHT RAYS ARE DISBURSEDINTO A WIDE RADIATIONPATTERN

LED LAMPDIFFUSED EXIT SURFACEENHANCES THE PROBABILITYOF LIGHT RAYS ESCAPING

Light Guides Around CornersLight guides may be bent to goaround corners. The bend radiusshould be equal to or greater thantwo thicknesses or twice thediameter of the light guide tominimize light loss. The light rayreflections follow the smoothcontour of the radius bend withoutloss, as shown in Figure 15. Sharpright angle direction changes maybe achieved by using a reflectiveprism design in the light guide atthe 90 bend location, as shown inFigure 16.

DIAMETER OR THICKNESS

LED LAMP

LIGHT GUIDE

LIGHT RAYREFLECTIONSFOLLOWCURVATURE OFLIGHT GUIDE

MINIMUM BEND RADIUS =2X DIAMETER OR THICKNESS

Figure 15. Light Guide with a 90 Bend. Light Rays are Scattered by Diffused ExitEnd.

Figure 16. Light Guide with Built in 45 Prism Reflector.

LIGHT GUIDE

SMT LED LAMP

PC BOARD

45 REFLECTIVEPRISM SURFACE

7

Wedge Light GuidesWedge shaped light guides may beused to achieve backlightingeffects. Two basic kinds are shownin Figure 17, the planar surfacewedge which gives a uniformdistribution of light and the curvedsurface wedge which gives a lightdistribution somewhat logarithmicin nature. The planar surfacewedge is typically used to back-light transreflective LCD displays.

Backlighting TransreflectiveLCD DisplaysTransreflective LCD displays maybe backlighted with LED lampsusing either a simple flat planarlight guide or a wedge light guide.For small area LCD displays, 1 to 2inches high by 2 to 4 inches wide, asimple flat planar light guide maybe used, as shown in Figure 18.The top surface of the light guide isdiffused to permit light toescape. The edges and backsideare smooth. The back surface iscoated with white light reflectingpaint. Two surface mount pc boardassemblies are mounted to thesides of the transparent plate foreven illumination. Optionalgrooves are cut into the plate toprovide alignment of the pc boardassembly with the plate. Thenumber of SMT LED lamps,spaced on 1/4 to 1/2 inch centers,depends upon the size of thetransparent plate and the requiredillumination.

A planar wedge light guide may beused with SMT LED lamps forbacklighting a medium sizetransreflective LCD display, i.e. 2to 3 inches high by 3 to 6 incheswide. A diffusing film interlayerbetween the LCD and the wedgeguide may be used to diffuse thelight, as shown in Figure 19. TheSMT LED lamps are spaced on 1/4to 1/2 inch spacing to achieve evenillumination. The SMT LED lamps

Figure 18. A Transreflective LCD Display Backlighted with SMT LED Lamps,Surface Mounted on Small PC Boards, Using a Simple Flat Planar Light Guide.

Figure 17. Wedge Light Guides, Planar Surface and Curved Surface.

SMT LED LAMP

WHITE REFLECTING PAINT OVERSPECULAR REFLECTING SURFACE

PLANAR SURFACEWEDGE GUIDE

CURVED SURFACEWEDGE GUIDE

PC BOARD

TRANSREFLECTIVE LCD

DIFFUSED SURFACE

SURFACEMOUNT

PC BOARDASSEMBLY

ALIGNMENT GROOVEBOTH SIDES

2.29 mm(0.090 IN.)

SMT LEDLAMP

WHITE PAINT

CROSS SECTIONAL END VIEW SHOWING RAY TRACING

8

are electrically connected in serieson the pc board assembly.

A right angle planar wedge lightguide may be used with SMT LEDlamps to backlight a medium sizedtransreflective LCD display that ismounted parallel to a surfacemount pc board assembly, asshown in Figure 20a. The SMT LEDlamps are spaced on 1/4 to 1/2 inchspacing to achieve even illumina-tion. The SMT LED lamps areelectrically connected in series onthe pc board assembly. The raytracing is shown in Figure 20b.

Figure 19. A Planar Wedge Light Guide used with SMT LED Lamps forBacklighting a Medium Size Transreflective LCD Display.

SURFACE MOUNTPC BOARD ASSEMBLY

WHITE REFLECTING PAINTON BACKSIDE SURFACE

PLANAR TRIANGULARLIGHT GUIDE

LCD DISPLAYMODULE

DIFFUSINGFILM

SMT LED LAMP

Figure 20a. A Right Angle Planar Wedge Light Guide used with SMT LED Lampsfor Backlighting a Medium Size Transreflective LCD Display.

Figure 20b. Ray Tracing Pattern for A Right Angle Planar Wedge Light Guide usedfor Backlighting a Medium Size Transreflective LCD Display.

LCD DISPLAYMODULE

RIGHT ANGLEPLANAR WEDGELIGHT GUIDEDIFFUSING FILM

SURFACE MOUNTPC BOARDASSEMBLY

SMT LED LAMPWHITE REFLECTINGPAINT ON BACKSIDE SURFACE

LCD DISPLAY MODULE

RIGHT ANGLEPLANAR WEDGE

GUIDE

DIFFUSING FILMWHITE LIGHT

REFLECTING PAINT

SMT LED LAMPCROSS SECTION SHOWING RAY TRACING

9

Untinted, nondiffused T-1 3/4 or T-1LED lamps can also be used with aright angle planar wedge lightguide as shown in Figure 21. Thespacing for these lamps is betweenadjacent placement and 3/4 inchescenters, depending upon thedesired luminance.

A dual right angle planar wedgelight guide may be used with SMTLED lamps to backlight a medium-large size transreflective LCDdisplay, 4 to 6 inches high by 6 to 9inches wide, that is mountedparallel to a surface mount pcboard assembly, as shown inFigure 22. The SMT LED lamps arespaced on 1/4 to 1/2 inch centers forboth light pipe wedges to achieveeven illumination. This techniquealso provides sufficient illumina-tion for bright ambient lightingconditions. The SMT LED lampsare electrically connected in series-parallel on the pc board assembly,one series string for each side ofthe light guide.

Diffusing FilmsDiffusing films are made withparticles that internally reflectincident light rays so that exit lightrays are scattered at randomangles, as illustrated in Figure 23.Diffusing films are lossy as some ofthe incidant flux, Ev(0)(lm/m2), isreflected and some of the flux isabsorbed. The remaining flux exitsthe diffusing film over a wideradiation pattern that can bedescribed by three parameters:1) Iv(0)(cd), the luminous intensityperpendicular to the surface of thefilm,2) 1/2 , the off-axis angle wherethe luminous intensity is 1/2 the on-axis value, and3) Lv(0)(cd/m2), the surfaceluminance.

A diffusing film with a Lambertian

Figure 21. A T-1 3/4 or T-1 Untinted, Nondiffused LED lamp Used as the LightSource for a Right Angle Planar Wedge Light Guide.

Figure 22. A Dual Right Angle Planar Wedge Light Guide used with SMT LEDLamps for Backlighting a Medium-Large Size Transreflective LCD Display.

Figure 23. Properties and Figures of Merit of a Diffusing Film.

RIGHT ANGLEPLANAR WEDGE

GUIDE

DIFFUSING FILMWHITE LIGHT

REFLECTING PAINT

LCD DISPLAY MODULE

T-1 3/4 OR T-1 LED LAMP

LCD DISPLAYMODULE

DUAL RIGHT ANGLEPLANAR WEDGE

LIGHT GUIDE

SURFACE MOUNTPC BOARDASSEMBLY

SMT LED LAMP

WHITE REFLECTINGPAINT ON SIDE

SURFACESWHITE REFLECTINGPAINT ON BACKSIDE

SURFACE

DIFFUSING FILM

Iv (0) LIGHT OUTPUTRADIATION PATTERN

Iv ( 1/2)2 1/2

2 1/2

1/2

DIFFUSING FILM

Ev(0): INCIDENT FLUX

FIGURES OF MERIT:Lv(0)Ev(0)

10

radiation pattern has a 1/2 valueof 60 degrees, and is the maximumviewing angle performance thatcan be achieved with a diffuser.

Figures of merit for comparing onediffusing film with another are:

Lv(0)(cd/m2)/Ev(0)(lm/m2) =The ratio of on-axis luminanceto incidant flux.

Where: Lv(0)(cd/m2) =Iv(0)(cd)/A(m2), andA(m2) = a selected area of

the diffusing film surface.

2 1/2 = The viewing cone angle.

Using these figure of merit param-eters, a trade-off between outputluminance and radiation patternmust then be made in selecting adiffusing film in order to achievedesired overall illuminationperformance in combination with alight guide. The higher the value ofthe Lv(0)/Ev(0) ratio, the brighteris the output luminance throughthe diffusing film for illuminatingan LCD display. Also, the wider isthe 2 1/2 angle, the better will bethe output radiation pattern(viewing cone angle) from thediffusing film, reducing the chanceof an LCD display appearingbrighter in the center than at theouter edges. The following compa-nies supply diffusing films:

Optical Systems3M Safety and Security SystemsDivision, 3M Center, Building 225-4N-14St. Paul, MN 55144-100001-(800)-328-7098Products:Diffusion Films:Type 100, 5 mils, 2 1/2 = 26.Type 070, 10 mils, 2 1/2 = 32.Type 050, 16 mils, 2 1/2 = 36.Type 040, 20 mils, 2 1/2 = 40

Brightness Enhancement Film(BEF)

Miles, Inc.Polymers DivisionMobay Road, Bldg. 8Pittsburgh, PA 15205-9741(412) 777-2000 FAX: (412) 777-2021Products: Makrofol BL 6-2:a pigment filled polycarbonatefilm, 8 and 16 mil thicknesses,2 1/2 = 18 and 36.Makrofol LT 6-4: a glass fiberfilled polycarbonate film, 16 to 20mil thicknesses, 2 1/2 = 16.

Physical Optics Corporation20600 Gramercy Place Bldg. 100Torrance, CA 90501(310) 320-3088 Fax: (310) 320-8067Products: Beam HomogenizingLight Shaping Diffusing Films.

Illumination PatternsLuminous intensity variations, asmeasured across the exit surfaceof a light guide or a light guide/diffusing film combination, deter-mine the evenness of illumination.The ideal would be to have aperfect rectangularly shapedillumination pattern so that theluminous intensity is the same atall points across the surface, theedges, the corners, and the centerall be at the same luminance. Anapproximation to this ideal isshown in Figure 24a, where theillumination is flat across thesurface, falling off smoothly at theedges. However, in a good designthere are typically minor luminousintensity variations across thesurface as shown in Figure 24b.These variations should notexceed 20% of the luminousintensity at the center.

Figures 24c - 24f show variousluminous intensity patterns thatproduce unacceptable illuminationvariations across the face of anLCD display and should beavoided. Careful optical design ofthe light guide and selection of theproper diffusing film to reduceluminous intensity variationsshould produce an acceptableillumination pattern equivalent toFigure 24a or 24b.

Backlighting Flat SurfaceAnnunciator Panels Made witha Diffusing FilmFlat plate light guides, wedge lightguides, and right angle and dualright angle wedge light guides, witheither SMT LED or standard T-1 3/4and T-1 LED lamps, are ideal forilluminating flat surface annuncia-tor panels. The techniques shownin Figures 18 through 24 directlyapply to annunciators that are thesame size as the LCD modules.Typically, annunciators are madeby silk-screening opaque lettersand symbols on the surface of adiffusing film, leaving open abackground area for illumination.The most effective approach is tosilk-screen the message on thebackside surface so it cannot bedamaged. The diffusing film isplaced directly onto the lightemitting surface of the light guideto form the annunciator unit. In theoff condition, the backgroundsurrounding the message is darkand without color. When illumi-nated, the bright color of the LEDlight readily signifies to an ob-server the on condition of theannunciator. The opaque lettersand symbols forming the messageare easy to read against the illumi-nated background.

11

100

80

60

40

20

0-3 -2 -1 0 1 2 3

RELATIVE LOCATION ACROSS SURFACE

REL

ATI

VE IN

TEN

SITY

, Iv

- %

CL

a. An Ideal Illumination Pattern. b. Achievable Good IlluminationPattern.

100

80

60

40

20

0-3 -2 -1 0 1 2 3

RELATIVE LOCATION ACROSS SURFACE

REL

ATI

VE IN

TEN

SITY

, Iv

- %

CL

100

80

60

40

20

0-3 -2 -1 0 1 2 3

RELATIVE LOCATION ACROSS SURFACE

REL

ATI

VE IN

TEN

SITY

, Iv

- %

CL

100

80

60

40

20

0-3 -2 -1 0 1 2 3

RELATIVE LOCATION ACROSS SURFACE

REL

ATI

VE IN

TEN

SITY

, Iv

- %

CL

100

80

60

40

20

0-3 -2 -1 0 1 2 3

RELATIVE LOCATION ACROSS SURFACE

REL

ATI

VE IN

TEN

SITY

, Iv

- %

CL

100

80

60

40

20

0-3 -2 -1 0 1 2 3

RELATIVE LOCATION ACROSS SURFACE

REL

ATI

VE IN

TEN

SITY

, Iv

- %

CL

These same concepts may beapplied to making small sizedannunciators utilizing the lightpipes described in the followingsection. In many cases, silk-screening an opaque background,leaving open letters or a symbol, ismost effective. The silk-screeneddiffusing film is glued to the exitsurface of the light pipe with anoptically clear adhesive to form theannunciator module. In the offcondition, the letters or symbol aredark and without color and tend toblend with the background. In theon condition, the bright letters orsymbol, with the color of the LEDlight, stand out vividly contrastingin appearance against the back-ground.

Figures a & b: Ideal and Achievable Illumination Patterns.

c. Center Illumination Brighter than atEdges.

d. Edge Illumination Brighter than atthe Center.

e. Uneven Illumination Across Surface. f. Illumination with a Center Hot Spot.

Figures c - f: Unacceptable Illumination Patterns.

Figure 24. Illumination Patterns of Various Light Guide/Diffusing FilmCombinations.

12

Figure 25. Simple Light Pipe Shapes for Use as Front Panel Indicators Using anSMT LED as the Light Source.

PC BOARD

SMTLED LAMP

LIGHT RAYREFLECTIONSFOLLOWCURVATURE OFLIGHT PIPE

COMPOUND CURVERECTANGULARLIGHT PIPE

DIFFUSEDEXIT END

Simple Shaped Light Pipes forFront Panel IndicationLight guides for front panelindication are typically called lightpipes. Light pipes can be made inmany simple and compoundshapes. Simple cylindrical, rectan-gular, and triangular shaped lightpipes are illustrated in Figure 25,utilizing an SMT LED as the lightsource. These simple light pipescan be made from commerciallyavailable plastic rod.

Custom Shaped Light Pipes forFront Panel IndicationCustom shapes, usually precisionmolded, are designed to achievespecial effects, as illustrated inFigure 26. Two or more LED lightsources may be needed to illumi-nate a large arrow shaped lightpipe. A three legged light pipemay be used to give a threecondition status in a single indica-tor, red for danger, yellow forcaution, and green for safe.

Compound Shaped Light Pipesfor Front Panel IndicationCompound light pipe configura-tions may also be precision moldedfor specialized applications. Theserpentine light pipe, shown inFigure 27, is designed to move lightaround an obstruction. The lightray reflections follow the curvatureof the light pipe without loss.

Multiple Element Light PipeArraysMultiple element light pipe arraysmay be molded as a single piecepart. Figure 28a shows a fourelement linear light pipe arraymolded as a single piece part. Thethickness of the tie plate (or tiebar) should be sufficient to providethe necessary level of support forcorrect positioning of each lightpipe element. For the assemblyshown, the 0.254 mm (0.010 in.)

Figure 26. Custom Shaped Light Pipes for Use as Front Panel Indicators.

Figure 27. A Serpentine, Rectangular Light Pipe Designed to Move Light Aroundan Obstruction.

SMT LEDs USED AS THE LIGHT SOURCEFOR THESE SIMPLE LIGHT PIPES

TWO SMT LEDsSAME COLOR RED YELLOW GREEN

THREE DIFFERENT COLOR SMT LEDs

13

thick tie plate is flexible, permit-ting manual adjustment of eachlight pipe as the array is installed inthe next assembly. The 2.54 mm(0.100 in.) thick tie bar in Figure28b is rigid, holding the fourserpentine bar elements in preciseposition to assure accurate place-ment into the next assembly. Sincethe thin tie plate and rigid tie barare perpendicular to the lightpipes, cross coupling of scatteredlight from an illuminated light pipeelement is minimal, and will notilluminate adjacent light pipeelements.

Tinted, Diffused vs. Untinted,Nondiffused LED Lamps asEmitters for Light PipesIn most cases, untinted,nondiffused LED lamps with semi-wide flux radiation patterns of 24degrees, or larger, are preferredemitters for light guides and lightpipes. However, there are designswhere a tinted, diffused LED lampwith a wide radiation pattern of 45to 60 degrees is the preferredemitter. This concept is illustratedin Figure 29. The semi-wideradiation pattern of a T-1 3/4untinted, nondiffused LED lampfits the requirements of a longslim light pipe. However, a shortstocky light pipe requires an LEDlamp with a wide flux radiationpattern to prevent a hot spottyappearance at the exit end thatmay be caused by using a lampwith a narrower radiation pattern.

Molded, Flexible, Diffused,Light Pipe ArraysFlexible, diffused, light pipe arraysare very effective in backlightingkeypads and indicator windows infront panel assemblies. Flexiblelight pipe arrays are usuallymolded from an untinted, diffused,optical grade silicone rubber, suchas 150-OU, supplied by ToryRubber Company, a division of

LIGHT PIPEELEMENT

ELEMENTTIE PLATE

0.254 mm(0.010 IN.)

Figure 28a. A Four Element Light Pipe Linear Array, Molded as a Single PiecePart with a Flexible Tie Plate.

Figure 28b A Four Element Serpentine Light Pipe Linear Array, Molded as aSingle Piece Part with a Rigid Tie Bar.

Figure 29. Conceptual Use of Tinted, Diffused and Untinted, Nondiffused LEDLamps as Emitters in Different Light Pipe Configurations.

LIGHT PIPE ELEMENTS

TIE BAR

2.54 mm(0.100 IN.)

LONG, SLIMLIGHT PIPE

T-1 3/4 UNTINTEDNONDIFFUSED

LED LAMPT-1 3/4 TINTED

DIFFUSEDLED LAMP

SHORT,STOCKY

LIGHT PIPE

14

Dow Corning. As illustrated inFigure 30a, the individual light pipeelements are short in length, areeither solid or hollow inside, andvary in size and shape. The SMTLED lamps fit up against the basesof solid light pipe elements, or fitinside hollow light pipe elements,as illustrated in Figure 30b. Thelight pipe array is placed over anSMT LED lamp pc board assemblyto form a backlighting unit, asillustrated in Figure 30b. A bright,wide angle illumination pattern isachieved at the exit end of eachlight pipe element. A pc boardassembly with standard T-1 3/4 orT-1 LED lamps may also be used,with the lamps fitting inside thehollow elements of the flexiblelight pipe array. The backlightingunit is then mated with the keypadand front cover to form the illumi-nated front panel assembly. Thepush button caps in the keypad aremolded from untinted, nondiffusedacrylic or polycarbonate. Theindicator windows in the frontcover are untinted and usuallynondiffused. Both the key caps andwindows may be diffused ifdesired. The wide illuminationpattern from each diffused lightpipe element assures an evenillumination and wide viewingangle for each push button cap andfront panel indicator window. Insome panel designs, the indicatorwindows are cut-outs in the frontpanel cover, allowing solid lightpipe elements to protrude about2.54 mm (0.100 in.). This makes apleasing design, adding somedepth to a front panel configura-tion.

The following company designsand molds flexible diffused lightpipe arrays for backlightingkeypads and indicator windows in

FLEXIBLE, DIFFUSEDLIGHT GUIDE ARRAYMOUNTED ONTOSMT LED PC BOARDASSEMBLY TO FORMBACKLIGHTING UNIT

PUSH BUTTONKEYPAD

FRONT PANELCOVER PLATE

ANNUNCIATORWINDOW

INDICATORWINDOWS

Figure 30a. A Molded, Flexible, Silicone Rubber, Untinted, Diffused Light PipeArray used in Combination with an SMT LED PC Board.

Figure 30b. The Flexible, Diffused Light Pipe Array and SMT LED PC Board Forma Backlighting Unit. This Backlighting Unit Illuminates a Push Button Keypad andFront Panel Assembly.

SMT LEDPC BOARDASSEMBLY

SMT LED LAMPS

MOLDED, FLEXIBLE,SILICONE RUBBER,UNTINTED, DIFFUSEDLIGHT GUIDE ARRAY

15

front panel assemblies. Diffusedsilicone rubber 150-OU is thematerial used.

Keytek44 Old State Road #3New Milford, CT 06776(203) 350-1153FAX: (203) 350-1155

Light Pipe Output Radiation PatternsThe light output radiation patternfrom the exit end of a light pipeshould be designed to meet theluminance and viewing anglerequirements in a defined ambientlighting environment. A trade-off ismade between on-axis intensityand radiation pattern, as illustratedin Figure 31. A wide radiationpattern, at the expense of on axisintensity, Iv (0), is better for a wideoff-axis viewing angle. This issuitable for most applications inmoderate ambient lighting condi-tions less than 1000 fc. For brightambient light conditions, such asfor outdoor viewing, radiationpattern is reduced to achieve ahigh on-axis intensity.

A designer may measure the lightoutput radiation pattern from theexit end of a light pipe using agoniometer. The goniometerrotating detector should be at anominal distance of 305 mm (12in.) from the exit end of the lightguide. Radiation pattern (viewingangle) curves are obtained, similarto those shown in Figure 32.

Figure 31. Wide and Narrow Light Pipe Radiation Patterns.

HIGH Iv(0)

A NARROW RADIATION PATTERNWITH HIGH INTENSITY FORBEST VIEWABILITY IN BRIGHTAMBIENT LIGHT CONDITIONS

A WIDE RADIATION PATTERNWITH MODERATE INTENSITY FOR BEST VIEWING ANGLE

MODERATE Iv(0)

100

80

60

40

20

0-90 -60 -30 0 30 60 90

OFF-AXIS 1/2 CONE ANGLES - DEGREES

REL

ATI

VE IN

TEN

SITY

, Iv

- %

CL

100

80

60

40

20

0-90 -60 -30 0 30 60 90

OFF-AXIS 1/2 CONE ANGLES - DEGREES

REL

ATI

VE IN

TEN

SITY

, Iv

- %

CL

A Wide Radiation Pattern for BestViewing Angle with Moderate On-Axis Intensity.

A Narrow Radiation Pattern with aSmall Viewing Angle and High On-Axis Intensity.

Figure 32. Wide and Narrow Light Pipe Output Radiation Patterns Obtained usinga Goniometer.

16

Edge Lighting a TransparentFlat Plate with Grid LinesA flat transparent plate withengraved or etched grid lines onthe face surface may be edgelighted with LED lamps, as shownin Figure 33a. The face surfaces ofa transparent flat plate are smoothfor an observer to see through. Thesurfaces of the grid lines are roughto give the necessary diffusingsurface. The grid lines may becoated with a thin layer of whitetranslucent paint to enhancedaylight readability, with some lossin grid illumination. All four edgesof the light plate may be paintedwith white reflecting paint.

Light within the light plate isinternally reflected by all surfaces,and escapes only through thediffused lines providing the gridline illumination, as shown inFigure 33b. Holes are drilled intotwo opposite ends to accept thedomes of HLMP-650X subminiaturelamps. The LED lamps are epoxiedto the transparent plate andelectrically wired in series. Therectangular bases of the LEDlamps are not inserted into thelight plate in order to keep theplate thickness at 2.54 mm (0.100in.). The number of LED lampsrequired, spaced on approximately1/4 to 1/2 inch centers, is deter-mined by the size of the light plateand the desired luminance of thegrid lines.

A transparent plate with engravedor etched grid lines may also beedge lighted using surfacemounted SMT LED lamps asshown in Figure 34. Two surfacemount pc board assemblies aremounted to the sides of thetransparent plate for even illumina-tion of the grid lines. Optionalgrooves are cut into the plate toprovide alignment of the pc board

Figure 33a. A Transparent Flat Plate with Engraved or Etched Grid LinesIlluminated by Subminiature LED Lamps, Epoxied to the Plate.

Figure 33b. Internal Reflecting Light Rays Escaping Only Through Engraved orEtched Diffused Grid Lines.

HLMP-650XSUBMINIATURELED LAMP

DIFFUSED SURFACE ENGRAVEDOR ETCHED GRID LINE

SMOOTH SPECULARREFLECTING SURFACES

SMOOTH SPECULARREFLECTING SURFACES

TRANSPARENT LIGHT PLATEWITH ENGRAVED OR ETCHEDGRID LINES

assembly with the plate. Thenumber of SMT LED lamps, spacedon 1/4 to 1/2 inch centers, dependsupon the size of the transparentplate and the required illuminationof the grid lines. Advantages of thisapproach are:

1) the minimum thickness of thetransparent plate, typically 2.29mm (0.090 in.) with optionalgrooves to enclose the SMT LED

lamps, or 2.03 mm (0.080 in.)without grooves for minimalplate thickness, and

2) the LED lamps are not epoxiedto the transparent plate.

SMOOTH,TRANSPARENTSURFACE,BOTH FACES

2.16 mm (0.085 IN.) DIA. DRILLEDHOLES TO INSERT DOMES OFHLMP-650X SERIES SUBMINIATURELED LAMPS, BOTH ENDS. NUMBER OF LAMPS DEPENDS ON SIZE OFPLATE AND DESIRED LUMINANCE.

2.54 mm(0.100 IN.)

ENGRAVED OR ETCHEDGRID LINES

OPTIONAL: ALL 4EDGES WITH WHITEREFLECTING PAINT

DIFFUSED SURFACEV GROOVE WITHRADIUS AT VERTEX

DIFFUSED SURFACERADIUS GROOVE

17

Light Guide VendorsThe following plastic moldingcompanies offer light guide opticaldesign assistance and/or candevelop prototypes.

Nitto Jushi Kogyo Co., LTD.Distributor: Astra Products Inc.P.O. Box 479, Baldwin, NY 11510(516) 223-7500 Fax: (516) 868-2371

C-Plastics, 243 T Whitney StreetLeominster, MA 01453(508) 534-6876 Fax: (508) 537-8238

Lexalite, 10163 US Highway 31 NorthP.O. Box 498, Charlevoix, MI 49720(616) 547-6584 Fax: (616) 547-5833

AO Tech, Division of American OpticalCorp., 14 Mechanics St., P.O. Box 746Southbridge, MA 01550(508) 765-9711 Fax: (508) 765-2158

NiOptics Corp. 1801 Maple Ave.Evanston, IL 60201(708) 491-2177 Fax: (708) 467-1244

Industrial Devices Inc. (IDI)260 Railroad AvenueHackensack, NJ 07601(201) 489-8989 Fax: (201) 489-6911

U.S. Precision Lens, 3997 McMann Rd.Cincinnati, OH 45245(513) 752-7000 Fax: (513) 752-2841

MIL-P-7788F LED LightedAircraft PanelFigure 35 illustrates the basicconstruction of an acrylic aircraftLED lighted panel assemblymeeting the requirements of MIL-P-7788F. This internally lighted paneluses HLMP-650X untinted,nondiffused, SMT subminiatureLED lamps surface mounted on adouble sided pc board. Maximummetalization is used on both sidesto achieve a low thermal resistanceto ambient.

The LED lamps are distributedthroughout the panel to achieve adesired lighting effect. Fluxcoupling into the panel is 100%.

Figure 34. A Transparent Flat Plate with Engraved or Etched Grid LinesIlluminated by SMT LED Lamps on Small Surface Mount PC Board Assemblies.

Light rays from the LED lampsblend together within the panel toproduce even illumination throughthe illuminated areas on the face ofthe panel. These illuminated areasare diffused and coated with a thinlayer of translucent white paint. Indaylight, the LED lamps are off,and the illumination areas appearwhite by reflecting ambient light.At night, these areas are internallyilluminated by the LED lamps andappear the same color as the LEDlight. All exterior surfaces of thepanel are painted with a whitereflecting paint, leaving open the

areas on the face of the panel to beinternally illuminated. An overcoatof black, scratch resistant paint isadded to form the exterior finish.The overall thickness of the panelis 5.84 mm (0.230 in.).

Coupling an Optical Fiber to anLED LampThe most effective method tocouple an optical fiber to an LEDlamp is to insert the fiber into thelamp package in close proximity tothe LED chip. This assures themost efficient flux coupling andlight capture by the optical fiber,

Figure 35. Basic Construction of a MIL-P-7788F LED Lighted Aircraft Panel,Shown in Simplified Cross Section.

TRANSPARENT ACRYLIC PLATE

SURFACEMOUNT

PC BOARDASSEMBLY

OPTIONAL ALIGNMENTGROOVE BOTH SIDES

2.29 mm(0.090 IN.)

SMT LEDLAMP

ENGRAVEDGRID LINES

ENGRAVEDGRID LINES

CROSS SECTIONAL END VIEWSHOWING RAY TRACING

5.84 mm(0.230 IN.)

METALIZATION VIA PC BOARD WITH MAXIMUMMETALIZATION, BOTH SIDES,FOR LOW THERMAL RESISTANCETO AMBIENT

OPTICAL GRADEACRYLIC PLASTIC

HLMP-650XSMT SUBMINIATURELED LAMP

DIFFUSED, TRANSLUCENTWHITE ILLUMINATED AREAEXTERIOR FINISH:OPAQUE BLACK

PAINT OVER WHITEREFLECTING PAINT

18

although only a small portion ofthe LED emitted flux is actuallycaptured by the fiber. The proce-dure is illustrated in Figure 36a.

1. With a jewelers lathe, cut off thetop of the dome package toobtain a flat, semi-smoothsurface.

2. Looking through the flat surfacewith a microscope, visuallylocate one corner of the LEDchip opposite the wire bond, as

shown in Figure 36b.3. Precision drill an insertion hole

down to the located corner,stopping at a minimum distanceof 0.5 mm (0.020 in.) above theLED chip. Do not come incontact with the wire bond orLED chip.

4. With a syringe, insert a clear,room temperature curing epoxyinto the hole.

5. Immediately insert the opticalfiber into the hole with a steady

rotary motion to assure no airbubbles.

6. Let the epoxy cure for therequired length of time.

The optical fiber is now anchoredto the LED lamp package. The fluxemanating from the corner of theLED chip is captured by theentrance end of the optical fiberwith minimal loss.

Figure 36a. Technique for Coupling an Optical Fiber to an LED Lamp

LED CHIP

WIRE BOND

CUT OFF TOP OFLAMP DOME TOOBTAIN FLATSURFACE

PRECISION DRILL HOLEINTO LAMP PACKAGEOPPOSITE WIRE BOND

OPTICAL FIBER

FILL HOLE WITH EPOXYAND INSERT FIBERWITH ROTARY MOTION

0.5 mm (0.020 IN.) MIN.CLEARANCE ABOVE

LED CHIP

A A

T-1 3/4 UNTINTED, NONDIFFUSED LED LAMP

WIRE BONDLED CHIP

REFLECTOR CUP

CATHODE LEAD

OPTICAL FIBERLOCATED OVER ONECORNER OF LED CHIPOPPOSITE WIRE BOND

PRECISION DRILLEDHOLE IN LAMP EPOXYDOME

ANODE LEAD

VIEW A-A

Figure 36b. Positioning of Optical Fiber With Respect to the LED Chip.

19

T-1 LED Lamps

Part Number LED and Color Viewing Angle Iv (20 mA) mcd

HLMP-K105 AS AlGaAs - 637 nm Red 45 65

HLMA-KL00 AS AlInGaP -592 nm Amber 45 200

HLMA-KH00 AS AlInGaP - 615 nm Red-Orange 45 200

HLMP-1340 GaP - 626 nm High Efficiency Red 60 55

HLMP-1440 GaP - 585 nm Yellow 60 45

HLMP-1540 GaP - 570 nm Green 60 45

20

T-1 3/4 LED Lamps

Part Number LED and Color Viewing Angle Iv, mcd (at 20 mA)Min. Typ.

HLMP-3750 GaP - 626 nm High Efficiency Red 24 90 125

HLMP-3850 GaP - 585 nm Yellow 24 96 140

HLMP-3950 GaP - 570 nm Green 24 111 265

HLMP-C025-P0000 AS AlInGaP - 625 nm Red 25 500 1000

HLMP-C225-O0000 AS AlInGaP - 590 nm Amber 25 450 800

HLMP-C625-P0000 AS AlInGaP - 637 nm Deep Red 25 500 700

HLMP-DB25-P0000 GaN - 462 nm Blue 25 40 100

HLMP-DM25-M0000 InGaN - 527 nm Green 25 245 970

HLMP-DS25-R0000 InGaN - 470 nm Blue 25 100 260

HLMP-EL24-PS000 AS AlInGaP - 590 nm Amber 23 765

HLMP-EG24-PS000 AS AlInGaP - 626 nm Red 23 765

HLMP-EL25-SV000 TS AlInGaP - 592 nm Amber 23 1650

HLMP-ED25-TW000 TS AlInGaP - 630 nm Red 23 2170

HLMP-EL30-MQ000 AS AlInGaP - 590 nm Amber 30 450

HLMP-EG30-NR000 AS AlInGaP - 626 nm Red 30 590

HLMP-EL31-SV000 TS AlInGaP - 592 nm Amber 30 1650

HLMP-ED31-SV000 TS AlInGaP - 630 nm Red 30 1650

HLMP-CB15-P0000 InGaN - 472 nm Blue 15 765

HLMP-CM15-S0000 InGaN - 525 nm Green 15 1650

HLMP-CB30-K0000 InGaN - 472 nm Blue 30 270

HLMP-CM30-M0000 InGaN - 525 nm Green 30 450

HLMP-EL24-SV000 AS AlInGaP - 590 nm Amber 23 1650

HLMP-EL30-SV000 AS AlInGaP - 590 nm Amber 30 1650

List of LED Lamps, Untinted, Nondiffused, Recommended for use in Light Guide Applications

Please request Agilent Technologies Surface Mount LED Selection Guide for full SMT LED offering.

SMT Subminiature LED Lamps

Part Number LED and Color Viewing Angle Iv (20 mA) mcd

HLMP-Q105 AS AlGaAs - 639 nm Red 28 200

HLMA-QL00 AS AlInGaP -592 nm Amber 15 500

HLMA-QH00 AS AlInGaP - 615 nm Red-Orange 15 500

HLMP-6305 GaP - 626 nm High Efficiency Red 28 40

HLMP-6405 GaP - 585 nm Yellow 28 20

HLMP-6505 GaP - 570 nm Green 28 40

SMT LED Lamps

Part Number LED and Color Viewing Angle Iv (20 mA) mcd

HSMH-A100 AS AlGaAs - 637 nm Red 120 50

HSMS-A100 GaP - 626 nm High Efficiency Red 120 15

HSMD-A100 GaP - 602 nm High Orange 120 15

HSMY-A100 GaP - 585 nm Yellow 120 15

HSMG-A100 GaP - 570 nm Green 120 15

HSMH-C191 AS AlGaAs - 637 nm Red 170 17

HSMS-C191 GaP - 626 nm High Efficiency Red 170 10

HSMD-C191 GaP - 602 nm High Orange 170 8

HSMY-C191 GaP - 585 nm Yellow 170 8

HSMG-C191 GaP - 570 nm Green 170 15

21

www.agilent.com/semiconductorsFor product information and a complete list ofdistributors, please go to our web site.

For technical assistance call:

Americas/Canada: +1 (800) 235-0312 or(408) 654-8675

Europe: +49 (0) 6441 92460

China: 10800 650 0017

Hong Kong: (+65) 271 2451

India, Australia, New Zealand: (+65) 271 2394

Japan: (+81 3) 3335-8152(Domestic/International), or0120-61-1280(Domestic Only)

Korea: (+65) 271 2194

Malaysia, Singapore: (+65) 271 2054

Taiwan: (+65) 271 2654

Data subject to change.Copyright 2001 Agilent Technologies, Inc.Obsoletes 5965-7399EDecember 7, 20015988-5086EN

Application Brief I-003What Is a Light Guide?Basic PrinciplesLight Guide DesignDiffusing FilmsIllumination PatternsLight Pipe Output Radiation Patterns