UV Light Ultraviolet Light - PowerPoint Presentation

Slide1

UV LightSlide2

Ultraviolet Light

Ultraviolet (UV) light falls in the range of the EM spectrum between visible light and X-rays

UV

light, which comes from the sun, is invisible to the human eye

.

It

makes black-light posters glow, and is responsible for summer tans — and sunburns

.

However, too much exposure to UV radiation is damaging to living tissue. Slide3

Ultraviolet Light

It

has frequencies of about 8 × 10

14

 to 3 × 10

16  hertz (Hz), and wavelengths of about 380 nanometers to about 10 nm.Slide4

Ultraviolet Light

UV is generally divided into three sub-bands:

UVA

, or near UV (315–400 nm);

UVB

, or middle UV (280–315 nm)UVC, or far UV (180–280 nm

)Slide5

Ultraviolet Light

Radiations with wavelengths from 10 nm to 180 nm are sometimes referred to as vacuum or extreme UV.

These wavelengths are blocked by air, and they only propagate in a vacuum.Slide6

UV Ionization

UV radiation has enough energy to break chemical bonds.

Due

to their higher energies, UV photons can cause ionization, a process in which electrons break away from atoms.

The

resulting vacancy affects the chemical properties of the atoms and causes them to form or break chemical bonds that they otherwise would not. Slide7

UV Ionization

This

can be useful for chemical processing, or it can be damaging to materials and living tissues.

This

damage can be beneficial, for instance, in disinfecting surfaces, but it can also be harmful, particularly to skin and eyes, which are most adversely affected by higher-energy UVB and UVC radiation. Slide8

UV Effects

Most of the natural UV light people encounter comes from the sun.

However

, only about 10 percent of sunlight is UV, and only about one-third of this penetrates the atmosphere to reach the

ground.Slide9

UV Effects

Of the solar UV energy that reaches the equator, 95 percent is UVA and 5 percent is UVB.

No

measurable UVC from solar radiation reaches the Earth's surface, because ozone, molecular oxygen and water vapor in the upper atmosphere completely absorb the shortest UV wavelengths.

Still

, "broad-spectrum ultraviolet radiation [UVA and UVB] is the strongest and most damaging to living thingsSlide10

Sunburn

A suntan is a reaction to exposure to harmful UVB rays.

Essentially

, a suntan results from the body's natural defense mechanism kicking in. 

This

consists of a pigment called melanin, which is produced by cells in the skin called melanocytes. Slide11

Sunburn

Melanin absorbs UV light and dissipates it as heat.

When

the body senses sun damage, it sends melanin into surrounding cells and tries to protect them from sustaining more damage.

The

pigment causes the skin to darken. Slide12

Sunburn

However, continued exposure to UV radiation can overwhelm the body's defenses.

When

this happens, a toxic reaction occurs, resulting in 

sunburn

. UV rays can damage the DNA in the body's cells.

The

body senses this destruction and floods the area with blood to help with the healing process.

Painful

inflammation occurs as well. Usually within half a day of overindulging in the sun, the characteristic red-lobster look of a sunburn begins to make itself known, and felt.Slide13

Sunburn

Sometimes the cells with DNA mutated by the sun's rays turn into problem cells that don't die but keep proliferating as

cancers.

The

UV light causes random damages in the DNA and DNA repair process such that cells acquire the ability to avoid

dying.Slide14

Sunburn

The

result is skin cancer, the most common form of cancer in the United States.

People

who get sunburned repeatedly are at much higher risk.

The risk for the deadliest form of skin cancer, called melanoma

, doubles for someone who has received five or more

sunburns.Slide15

Other Sources of UV

Artificial sources

include:

tanning booths

black lights

curing lamps germicidal

lamps

mercury

vapor

lamps

halogen lightsSlide16

Fluorescence

Many substances — including minerals, plants, fungi and microbes, as well as organic and inorganic chemicals — can absorb UV radiation.

Absorption

causes electrons in the material to jump to a higher energy level.

These

electrons can then return to a lower energy level in a series of smaller steps, emitting a portion of their absorbed energy as visible light. Slide17

Fluorescence

Materials

used as pigments in paint or dye that exhibit such fluorescence appear brighter under sunlight because they absorb invisible UV light and re-emit it at visible wavelengths.

For

this reason they are commonly used for signs, safety vests and other applications in which high visibility is important. Slide18

Fluorescence

In

fluorescent tubes used for lighting,

ultraviolet

radiation with a wavelength of 254 nm is produced along with the blue light that is emitted when an electric current is passed through mercury

vapor. This ultraviolet radiation is invisible but contains more energy than the visible light emitted. Slide19

Fluorescence

The energy from the ultraviolet light is absorbed by the fluorescent coating inside the fluorescent lamp and re-emitted as visible light.

Similar tubes without the same fluorescent coating emit UV light that can be used to disinfect surfaces, since the ionizing effects of UV radiation can kill most bacteria. Slide20

Fluorescence

Black-light tubes typically use mercury vapor to produce long-wave UVA light, which causes certain dyes and pigments to fluoresce.

The

glass tube is coated with a dark-purple filter material to block most of the visible light, making the fluorescent glow appear more pronounced.

This

filtering is not needed for applications such as disinfecting.