LIGHTING:FLUOR ESCENT LIGHTS.

FLUOR ESCENT LIGHTS

To understand how fluorescent lights work, it is helpful to remember that light results from the energy emitted when excited electrons return to their ground state. A fluorescent light contains a central element in a long sealed glass tube. This tube is typically filled with an inert gas, such as argon, and a small bit of mercury vapor. In addition, a phosphor powder is coated along the inside of the glass tube. When current is applied to the ends of the tube, electrons migrate through the gas from one end of the tube to the other. As the electrons move through the tube, some of them collide with gaseous mercury atoms. This collision promotes electrons in the mercury atom to a higher energy level. As these elec- trons revert back to their original energy level, they emit energy in the form of photons. The wavelength of the light emitted is a function of the energy difference between the ground state and the excited state. In a fluorescent tube, the mercury atoms release photons in the ultraviolet wavelength of the spectrum. This ultraviolet light is converted to visible light by the phosphors that coat the interior surface of the tube. When the photons emitted from the mercury collide with the phosphor coating, they transfer their energy, bumping the electrons of the phosphor to a higher energy level. The phosphor then releases photons as emitted light in the visible wavelengths. The phosphor is responsible for giving off the characteristic white light that we are familiar with. Varying com- positions of phosphors can give different color fluorescent lights. As dis- cussed later, incandescent bulbs waste a great deal of energy producing infrared light that is not seen by the human eye. Since fluorescent lamps yield a greater amount of visible light under the same circumstances, they are typically about five times more efficient than incandescent light bulbs. In contrast to traditional light sources, such as incandescent and halogen bulbs, fluorescent lights require a much higher voltage to operate. This is because of the greater resistance the electrons encounter moving through a gas instead of through a filament. It takes some time to heat the electrons in the tube to a temperature at which they will start to emit radiation in the form of photons. This is why fluorescent tubes sometimes take a second to light up when the current is applied. Trans- formers, which convert normal voltage to a much higher voltage, are used to apply higher-energy electrons to the light tube and ensure that the atoms emit photons of the proper wavelength. Fluorescent light tubes do contain a small amount of mercury vapor that can be toxic to humans. Therefore, great care should be exercised when cleaning up broken fluorescent light tubes.