Science Projects
Fluorescent Blues (and Yellows)

Items needed:
	A Fluorescent Light
	Aluminum Foil

Tear off a piece of foil about 3 inches wide and as long as the roll of foil is wide. Fold this strip in half, with the shiny side out, so that it is 1.5 inches wide. Then fold it in half again, and again, so that you have a long, thin wand of foil. Place it on a hard surface and rub your finger over it to make if very smooth and shiny.
Hold the foil wand about a foot or more under the fluorescent bulb. Swing the wand back and forth very quickly, watching carefully. You should see bands of yellow and blue light reflecting on the foil. Not all fluorescent bulbs will do this, but most do. If the one you are trying does not work, try a different one.

Why? Why do you see the bands of color? It has to do with the way a fluorescent light works. Most fluorescent bulbs have had the air inside removed and replaced by a small amount of mercury vapor and argon gas. These gases are at very low pressure. The inside of the glass tube is coated with a white powder, called the phosphor.
When you turn on the light, a burst of electricity causes the gas mixture to give off blue and ultraviolet light. Your eye cannot see the ultraviolet light, but when it hits the phosphor powder, the powder glows brightly. If the electricity was constant, you would not see the bands of color, but the electric current is alternating current. The electricity flows one way, stops, flows the other direction, stops and then back in the original direction again. The electricity in your house alternates back and forth 60 times each second. (50 times per second for some countries.) While the electricity is flowing, you see mostly the blue light from the argon gas. When the electricity stops, you see the residual glow from the phosphor powder, which is yellow. The colors change so quickly that your eye combines the two colors. If you mix blue and yellow paint, you get green. If you mix yellow and blue light, you get white. Yes, that is not a typo. White. Just like the white light you see from the fluorescent light bulb.

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