Thursday, July 7, 2011

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.

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

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...

...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:

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.

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)

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))



  1. Good job! I did not know that!

  2. What is nm
    How does ultraviolet allows you to analyse crime scenes (body fluids like saliva and semen fluoresce), control pests by tracking urine trails etc. Cant they be seen with naked eyes?

  3. Ahem. Nm is nano meter (10^-9 m). Body fluids contain fluorescent substances. So does the urine. Its the minerals that cause the fluids to glow. The glow can be seen with human eyes.