The use of fluorescent powder in inner wall of mercury tube helps to convert that UV rays into visible light rays.
A fluorescent lamp, or fluorescent tube, is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow.
Mercury is used in a variety of light bulbs. Mercury is useful in lighting because it contributes to the bulbs' efficient operation and life expectancy. Fluorescent and other mercury-added bulbs are generally more energy efficient and last longer than incandescent and other equivalent forms of lighting.
An average of 4 milligrams (mg) of mercury is in a CFL. A mercury thermometer may contain about 500 mg of mercury. About 500 mg to 700 mg or less of mercury is considered a small spill. Some CFLs may contain as little as 1.4 mg to 2.5 mg per light bulb.
In short, the exposure from breaking a compact fluorescent bulb is in about the same range as the exposure from eating a can or two of tuna fish. ... The tiny amount of mercury you're exposed to when breaking a CFL is extremely unlikely to cause any ill effects, noticeable or otherwise.
Mercury-containing light bulbs include: fluorescent bulbs, including compact fluorescent light bulbs (CFLs); high intensity discharge (HID) bulbs, which include mercury vapor bulbs, metal halide and high-pressure sodium bulbs, and are used for streetlights, floodlights, parking lots, and industrial lighting.