Fluorescent lights are the most energy saving lamp. A fluorescent lamp is a glass tube, filled with argon, or argon/krypton gas, and mercury. When turned on, the mercury vapors get ionized and emit ultra-violet (UV) radiation, striking the phosphor coating on the tube, causing it to glow — or fluoresce. That is the process that produces light. About 22% of the energy used by the lamp is converted to light.

As with incandescents, there are tradeoffs with fluorescents. For example, all fluorescents contain mercury — which means that disposal of any fluorescent bulb is potentially an environmental hazard. 620 million fluorescent lamps are discarded annually in the US, releasing from 2 to 4 tons of mercury per year. Obviously, a hazardous situation as mercury leaches into our water systems. Additionally, fluorescents require an appropriate ballast and regular exposure to fluorescent lighting has been known to cause or contribute to health problems — especially where there is more flicker and hum.
All ballasts generate noise and carry sound level ratings A, B, C, or D. An “A” rated ballast typically hums softly; a “D” rated ballast typically buzzes rather loudly. Electronic ballasts produce less flicker and emit less of a humming noise.
Compact Fluorescent Lights (CFLs) are miniature versions of full-sized fluorescents. Those qualified under the Energy Star program are 3-4 times more energy efficient than standard incandescent bulbs and last up to 10 times longer. Although energy -efficient, they do have some tradeoffs to be aware of. They are a more diffuse light than incandescent and not appropriate everywhere. For example, they do not produce enough light for many reflector fixtures.
Fluorescent Mercury Vapors: When purchasing fluorescent bulbs, choose low-mercury, non-leachable bulbs. When broken, fluorescent lighting can release mercury vapors into your personal space and into the atmosphere. Precautionary care is needed to prevent breathing in these vapors when a fixture breaks near you.
Fluorescent Mercury Disposal: Under Federal regulations, businesses can no longer dispose of spent fluorescent light bulbs, lamps, ballasts or other lights containing mercury as unregulated refuse. For homeowners, it may be challenging in your area to find where you can dispose of these items properly to keep mercury from leaching into land and water. Your trash barrel won't do. The Association of Lighting and Mercury Recyclers (ALMR) offers further information on lamp recycing in the U.S. located on the EPA's website at www.epa.gov.