Visible Light

Wavelengths smaller than infrared (about the size of protozoans)

Frequencies above infrared

Light we can see with our eyes

Visible light is made up of the colors of the spectrum(ROYGBV)

Uses of Visible Light

• Use it to see • Take photographs with it• Used in photosynthesis• Solar Heat• Lasers are single spectrum light

– Used in Compact Disc and DVD players – Laser printers– photoelectric copying machines– FAX machines– optical recording media– optical disc mass-storage systems– Supermarket scanners– Fiber optics

 

How the Eye Sees

• http://www.preventblindness.org/vlc/how_we_see.htm

• http://www.glenbrook.k12.il.us/gbssci/Phys/Class/light/u12l2b.html

Photosynthesis• 6H2O + 6CO2 ----------> C6H12O6+ 6O2

• Essential to almost all life on Earth• Takes energy of light and converts it to chemical

energy• Produces oxygen on the planet so we can

breathe• Without visible light there would be no food on

the planet

Solar Cells

• The solar cells that you see on calculators are photovoltaic cells which convert sunlight directly into electricity. Photovoltaic (PV) cells are made of special materials called semiconductors such as silicon, which is currently the most commonly used. Basically, when light strikes the cell, a certain portion of it is absorbed within the semiconductor material transfering the energy of the absorbed light to the semiconductor. The energy knocks electrons loose, allowing them to flow freely. PV cells also all have one or more electric fields that act to force electrons freed by light absorption to flow in a certain direction. This flow of electrons is a current, and by placing metal contacts on the top and bottom of the PV cell, we can draw that current off to use.

How CD’s/DVD’s Work

The incredibly small dimensions of the bumps make the spiral track on a CD extremely long. If you could lift the data track off a CD and stretch it out into a straight line, it would be 0.5 microns wide and almost 3.5 miles (5 km) long!

CD’s Continued• The CD player finds and reads the data stored as bumps. The drive consists

of three fundamental components:

• A drive motor spins the disc. This drive motor is precisely controlled to rotate between 200 and 500 rpm depending on which track is being read.

• A laser and a lens system focus in on and read the bumps.

• A tracking mechanism moves the laser assembly so that the laser's beam can follow the spiral track. The tracking system has to be able to move the laser at micron resolutions.

• http://electronics.howstuffworks.com/cd5.htm Check out what happens next

Fiber Optics

• Long, thin strands of very pure glass about the diameter of a human hair

• Are used to transmit cable TV, internet, and phone

• An optical fiber, has the following parts:

• Core - Thin glass center of the fiber where the light travels

• Cladding – Surrounds the core and reflects the light back into the core

• Buffer coating - Plastic coating that protects the fiber from damage

• Transmits light by principle of total internal reflection

Medical Applications

• Light therapy or phototherapy consists of exposure to daylight or to specific wavelengths of light using lasers, LEDs, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, for a prescribed amount of time and, in some cases, at a specific time of day. It has proven effective in treating Acne vulgaris, seasonal affective disorder, and is part of the standard treatment regimen for delayed sleep phase syndrome. It has recently been shown effective in non-seasonal depression. Proponents claim demonstrable benefits for skin conditions such as psoriasis.

Medical Applications of Lasers• Laser Eye Surgery: Lasers are very useful in treating far sightedness and

cataracts, among other eye surgeries. Because the laser beam is so minute and intense, it can burn through a very small amount of eye tissue. By focusing the laser on the point of tissue that is damaged, it can easily be corrected without damaging surrounding tissue that is in good condition. Without lasers, it would have been difficult to reach such hard to access areas and treat eye problems.

•  Laser Ulcer Removal: Ulcers in the stomach can be very effectively removed with lasers. The laser beam used as a scalpel, is capable of making a tiny incision to reach the ulcer. Because of the burning action of lasers, the cut is also clotted and sealed immediately. The loss of blood is thus very minimal, and recuperation is also faster with laser ulcer surgery.

• Lasers to remove Port Wine Stains: Many people have an accumulation of red blood cells just under their skin, which results in red marks, called port wine stains. Laser surgery is very effective in removing these marks, without damaging the outer skin surface and the surrounding blood cells.

Dangers

• Too much light can damage the retina in your eye. This can happen when you look at something very bright, such as the Sun. Although the damage can heal, if it's is too bad it'll be permanent.

                                                    

                

Ultraviolet Light

• Wavelengths about the size of a molecule

(smaller than visible light)

• Frequencies higher than visible light

• First form of radiation considered to be ionizing radiation

Types of UV Light• UVA (long wavelength low frequency)

does not cause sunburn but does cause damage to collagen fibers and destroys vitamin A in skin can cause skin cancer indirectly

• UVB causes sunburn and can directly damage DNA causing skin cancers

• UVC from the sun is blocked by ozone layer (has highly energetic photons)

Dangers of UV

• In human beings, skin exposure to UVC light can produce sunburn and (in some cases) skin cancer.

• Exposure of the eyes to this UV radiation can produce extremely painful inflammation of the cornea and temporary or permanent vision impairment, up to and including blindness in some cases.

• UV can damage the retina of the eye. • Can cause cataracts over time• Causes photoaging-many of the symptoms commonly associated

with mere aging (i.e. wrinkles, loosening of the skin) may instead be related to UV exposure

Damage to DNA= Cancer

Ultraviolet photons harm the DNA molecules of living organisms in different ways. In one common damage event, adjacent Thymine bases bond with each other, instead of across the "ladder". This makes a bulge, and the distorted DNA molecule does not function properly.

Ionizing Radiation

• Ionizing radiation consists of subatomic particles or waves that are energetic enough to detach electrons from atoms or molecules, ionizing them.

• The negatively-charged electrons and positively charged ions created by ionizing radiation may cause damage in living tissue. If the dose is sufficient, the effect may be seen almost immediately, in the form of radiation poisoning. Lower doses may cause cancer or other long-term problems.

Skin Cancer

• Melanoma – cancer in melanocytes (skin cells that make pigment)

• basal cell carcinoma-cancer that forms in small, round cells in the base of the outer layer of skin)

• squamous cell carcinoma-cancer that forms in flat cells that form the surface of the skin

Types of Skin Cancer

Melanomas

Skin Cancer Statistics• Skin cancer is the most common form of cancer in the US with more

than one million skin cancers diagnosed annually.• One in five Americans will develop skin cancer in their lifetime.• Basal cell carcinoma (BCC) is the most common form of skin

cancer. They are rarely fatal, but can be highly disfiguring.• Squamous cell carcinoma (SCC) is the second most common form

of skin cancer. More than 250,000 cases are diagnosed each year, resulting in approximately 2,500 deaths.

• About 90% of non-melanoma skin cancers and 65 % of melanoma cases are associated with exposure to ultraviolet (UV) radiation from the sun.

• Up to 90% of the visible changes commonly attributed to aging are caused by the sun.

• People who use tanning beds are 2.5 times more likely to develop squamous cell carcinoma and 1.5 times more likely to develop basal cell carcinoma.

Uses of UV Light• Can be used to detect forged bank notes • Can be used to harden some types of dental filling. • UV lamps (blacklights) used in clubs to make your clothes glow-

substances in laundry detergent "fluoresce" when UV light strikes them (they absorb the UV and re-radiate the energy as visible light)

• Ultraviolet rays can be used to kill microbes. • Cause the body to produce vitamin D• UV light is also used as a therapy for psoriasis, a condition in which

the skin sheds its cells too quickly, resulting in itchy, scaly patches on various parts of the body. When exposed to ultraviolet rays, the growth of the skin cells is slowed, relieving the symptoms.

• Certain animals can actually see ultraviolet light, and use it to their advantage. Bees use the reflection of UV off of flower petals to guide their pollen collecting.

• Can be used to attract bugs to bug zappers

Use of UV Light to Sterilize

• food, air and water purification• Kills bacteria, viruses and molds• destroys the nucleic acids in these organisms so that their DNA is

disrupted by the UV radiation removing their reproductive capabilities and killing them

• Used in hospitals and operating rooms to kill germs in air and on equipment

• Uses UV-C

Production of Vitamin D•Vitamin D sufficiency prevents rickets in children and osteomalacia in adults •Together with calcium, vitamin D also helps protect older adults from osteoporosis•Improves neuromuscular and immune function and reduction of inflammation•Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by vitamin D•May protect against breast, colon, and prostate cancer•May impact glucose resistance and prevent diabetes •May protect against development of autoimmune disorders like MS, rheumatoid arthritis

if you live north of about 37o (roughly, a line from Richmond to San Francisco), you will be exposed to little UVB from at least November through February because the sun’s zenith angle is so low that the atmosphere absorbs most UVB before it reaches you.

Use of UV by Insects

Arnica angustifolia in visible light The same plant as seen in UV light

•Some species of flying insect such as houseflies and bluebottles, wasps, mosquitoes, and bees can see ultraviolet light•Bees use UV light patterns on flowers to locate pollen and nectar stores

UV and the Ozone Layer• Extra UV can harm phytoplankton in the oceans. Because this type

of plankton is the first link of the marine food chain, variations in its population could potentially cause greater disturbances in the balance of other life forms like fish or whales.

•  Greater exposure of plant life to UV-B can result in a decrease in production rates, meaning less food available world-wide. 

Ozone and oxygen molecules in the stratosphere absorb ultraviolet light from the sun, providing a shield that prevents this radiation from passing to the earth's surface. While both oxygen and ozone together absorb 95 to 99.9% of the sun's ultraviolet radiation, only ozone effectively absorbs the most energetic ultraviolet light, known as UV-C and UV-B, which causes biological damage. The protective role of the ozone layer in the upper atmosphere is so vital that scientists believe life on land probably would not have evolved - and could not exist today - without it.