Visible Light

1
Visible Light

• Wavelengths smaller than infrared (about the size
  of protozoans)
• Frequencies above infrared
• Light we can see with our eyes

2
Visible light is made up of the colors of the
spectrum(ROYGBV)
3
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

 


4
How the Eye Sees

• http//www.preventblindness.org/vlc/how_we_see.htm
  
• http//www.glenbrook.k12.il.us/gbssci/Phys/Class/l
  ight/u12l2b.html

5
Photosynthesis

• 6H2O 6CO2 ----------gt 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

6
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.

7
How CDs/DVDs 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!
8
CDs 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

9
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

10
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.

11
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.

12
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.

                                                                    
13
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

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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)

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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

16
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.
17
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.

18
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

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Types of Skin Cancer
Melanomas
20
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.

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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

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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

23
Production of Vitamin D
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 suns zenith angle
is so low that the atmosphere absorbs most UVB
before it reaches you.

• 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

24
Use of UV by Insects

• 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

Arnica angustifolia in visible light
The same plant as seen in UV light
25
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.