382. I've heard (from observations recorded in an office environment) that fluorescent light bulbs "emit" their energy at a certain frequency. If this frequency is at or below the rate at which our eyes blink/scan, this will cause eye fatigue and other health "problems." What would be the best light system for the office environment?
Fluorescent light bulbs flicker rapidly because they operate directly from the alternating current in the power line. The light that you see is emitted by a coating of phosphors on the inside surface of the glass tube. These phosphors receive power as ultraviolet light and emit a good fraction of that power as visible light. The ultraviolet light comes from an electric discharge that takes place in the mercury vapor inside the tube. Since this electric discharge only functions while current is passing through the tube, it stops each time the current in the power line reverses. Thus, with each reversal of the power line, the discharge ceases, the ultraviolet light disappears, and the phosphors stop emitting visible light. So the tube flickers on and off. However, the alternating current in the United States reverses 120 times a second in order to complete 60 full cycles each second. The fluorescent lamps flicker 120 times a second. Even the very best computer monitors don't refresh their images that frequently because our eyes just don't respond to such rapid fluctuations in light intensity. In short, you can't see this flicker with your eyes. If you get eye fatigue from fluorescent lamps, it's the color or intensity of the light that's bothering you, not the flicker. It's just too fast to affect you.