Ultraviolet Light: by Jonan, Min Suk and Yu Xiang

What is Ultraviolet light?
Ultraviolet light is the wavelength of the electromagnetic spectrum where:
- Wavelengths range from 400nm to 10nm
- Energy per photon is 3-124 eV (where 1eV is equivalent to 1.602×10^−19 J)
Ultraviolet light has a wavelength beyond the color violet, which is why its called ultra(beyond)violet.

Discovery
UV radiation was discovered by:
- Johann Wilhelm Ritter in 1801
- Victor Schumann is 1893 (who discovered UV rays with wavelengths below 200nm)

Properties
UV light is capable of:
- causing fluorescence in otherwise non-luminescent objects
- causing damage to DNA
- ionizing gas
UV light is also released by astronomical objects and it can be seen by some animals.

These main capabilities of UV light therefore make it useful in a number of...

Applications
...where UV light is used to:
- prevent counterfeiting through the inclusion of fluorescent materials into debit cards and banknotes
- analyse crime scenes (body fluids like saliva and semen fluoresce)
- operate fluorescent lamps by causing the mercury vapor within to fluoresce
- view astronomical objects (like the Sun)
- identify animals that fluoresce under UV light
- control pests by tracking urine trails
- purify air and water through UV irradiation

Other application for UV light by wavelength are: (list sourced from Wikipedia. url:http://en.wikipedia.org/wiki/Ultraviolet#Applications_of_UV

13.5 nm: Extreme Ultraviolet Lithography
230-400 nm: Optical sensors, various instrumentation
230-365 nm: UV-ID, label tracking, barcodes
240-280 nm: Disinfection, decontamination of surfaces and water (DNA absorption has a peak at 260 nm)
250-300 nm: Forensic analysis, drug detection
270-300 nm: Protein analysis, DNA sequencing, drug discovery
280-400 nm: Medical imaging of cells
300-400 nm: Solid-state lighting
300-365 nm: Curing of polymers and printer inks
300-320 nm: Light therapy in medicine
350-370 nm: Bug zappers (flies are most attracted to light at 365 nm)

Types of UV light
Like visible light, UV light has multiple distinct wavelengths possessing unique properties. There are 3 main types of UV light:
- Ultraviolet A, long wave UV or black light, λ of 400-315 nm
- Ultraviolet B, medium wave UV, λ of 315-280 nm
- Ultraviolet C, short wave UV, germicidal UV, λ of 280-100nm
UV light with wavelengths ranging from 200-10nm are strongly absorbed by oxygen in the air. Oxygen is opaque at those wavelengths.

Sources
UV light is produced through natural and artificial means like:
- The Sun (which produces UVA, UVB and UVC)
- Black lights (producing mainly UVA and some visible light)
- Ultraviolet lasers (producing high UVA to low UVC)

Hazards
UV light is as dangerous as it is beneficial. UV light is partially responsible for:
- Skin cancer
- Skin aging
- Sunburn (which can happen for both your skin and your EYES (where it is called arc eye))

Sources:
http://en.wikipedia.org/wiki/Ultraviolet
http://science.hq.nasa.gov/kids/imagers/ems/uv.html
http://www.nas.nasa.gov/About/Education/Ozone/radiation.html