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Matthew Hutchins' Physics of UltraViolet Light
Portions of UV Lighting
Sample Problems


Fluoresces are basically when a substance absorbs a high energy wave, normally UV, and it is re-emitted at a lower energy, normally in the visible region, causing it to have a glowing neon color.


This is the basic principle on how all fluorescent lighting works, such as the ones is offices and schools. These lights are glass tubes that contain small amounts of mercury vapor. When electricity is discharged through is it causes the valence electrons to excite and jump to their next orbital and as they fall back into their correct orbital they release energy that is in the UV portion of the spectrum (seeing as how I have not cited myself yet; that explanation was all due to the wonderful teachings of Mr. Schaap). Back to my project now! As the UV lighting (specifically UVC) is emitted it could be dangerous to humans so it is incased in glass. Glass absorbs UV light and does not allow it pass trough it. So how does the UV light turn to visible light? Well this is where fluorescence come into play. The inside is coated with phosphor which uses the first principle described to emit light in the visible region.

For tanning beds a similar lighting techniques are used, but instead of glass it uses a material that allows the UV rays to pass through without being absorbed as much, such as quartz.

A similar principal to fluorescence is Phosphorescence. Basically this is when energy is placed in materials and due to a quantum limitation can only be emitted slowly. you see this mostly with glow-in-the-dark objects, such as the stars that people put on their bedroom ceiling that glow green at night. These substances can emit low levels of light for hours.

(Mr. Bowers I should get extra credit for making sense of this mumbo-jumbo, in case my explanation was not up to physics standards heres the official definition of Phosphorescence...)

Phosphorescence is the result of a radiative (light emitting) transition involving a change in the spin multiplicity of (in most cases) a molecule from excited state singlet to excited state triplet. This transition is quantum mechanically forbidden as is the transition that leads to light emission. These forbidden transitions are kinetically slow, which introduces a delay between photo- excitation (exposure to light of one wavelength ) and emission (release of light of a different wavelength ). So-called "glow in the dark" materials are phosphorescent materials with a very long (seconds, minutes, even hours) delay between excitation and emission. Most phosphorescent compounds have triplet lifetimes on the order of milliseconds.


Another use of fluorescence is pest control. Bug zappers have a fluorescent bulb that emits low UV radiation, which they are attracted to and then they get caught in a metal netting with an electric current flowing threw it. If you know about electricity you may ask how a bug gets ''zapped'' when they are not grounded? (I know I did, so I got side tracked and looked it up). There are actually 2 wire nets separated about the same space as the average insect. One is electrified and one id grounded. When they fly through they complete the circuit and ZAP! The average Bug zapper has a transformer to go from the standard 120V to 2000V. If it had a standard 10 amp current, then it would have 200 ohm resistance. (V=IR)

(Ha, see I did my project on light and electricity. I'm also totally off topic!)

Also most fly papers are coated with fluorescent dyes and attract flys to the sticky surface and the eventually get stuck and die. Similar to a spider web. (Isn't it funny how so many inventions are modeled after nature?)

Continue to Citaion!

İMatthew Hutchins 2005