Question

Is there any way to see ultra violet light, or make it?

Asked by: Alex Reinisch

Answer

By definition, ultraviolet light is 'beyond violet light' and the visible spectrum that can be detected by the human eye. It cannot, therefore, be seen directly. Detectors that are sensitive to UV convert it into a form that we can see. Technically, you can 'see' the UV part of the electromagnetic spectrum if you and the source of UV radiation are receding from each other at a high enough velocity to red-shift high frequency UV waves into the visible spectrum. In this scenario, however, UV light is being emitted, not received.

You don't need to make it artificially, since the Sun emits UV rays that penetrate the upper atomosphere's ozone layer to different extents. Those rays are responsible for sunburn, deterioration of some materials, and other effects. They can also be made artificially...just visit the nearest tanning bed for all the UV rays you want.

Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor



Ultraviolet (UV) light is basically light that has a shorter wavelength (and higher frequency) than visible light. Typically anything with a wavelength between 4 nm and 400 nm (nm = nanometer = 10-9 m) is called UV light. So called near UV is in the range 400-300 nm, far UV is in the range 300-200 nm, and extreme or vacuum UV is anything below 200 nm. The Sun is a strong UV emitter but only near UV reaches the surface of the Earth because the ozone in the atmosphere absorbs all wavelengths below 290 nm.

Artificially, UV light is usually produced with mercury-vapour and deuterium lamps. The trouble is that these lamps also produce a certain visible light content. So when you turn them on they glow white or pink. However, one can make 'pure' UV of a single wavelength using a laser. Usually a frequency-doubled argon gas is used to produce a continuous wave beam of UV light. This beam, say at 244 nm or 300 nm, can not be seen at all with a human eye. However if you put a piece of paper in its path the paper will glow blue. This happens because the UV excites blue dyes in the paper (the paper manufacturers put blue dyes in all papers to make them appear more 'white'). This also happens to your white shirts when you walk under a 'dark UV lamp' in a disco bar or in one of those stores that sell glow in the dark stuff.

Answered by: Anton Skorucak, M.S. Physics, President and creator of PhysLink.com

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