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Compact fluorescent lamp

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A three-U's type compact fluorescent lamp, popular with North American consumers since the mid-1990s.

A compact fluorescent lamp (CFL), is a type of lamp (light bulb) designed to fit into the same space and usually also socket as an incandescent bulb, but with the advantages of a fluorescent lamp. Many CFLs can directly replace an existing incandescent lamp.

The purchase price of a CFL is often much higher than an incandescent lamp of the same output, and the light from CFLs looks different to light from incandescent lamps.[1] CFLs have a longer rated life and use less energy than an incandescent lamp of the same brightness. A CFL can save over US$30 in electricity costs over the lamp’s lifetime compared to an incandescent lamp.[2]

How it works

An electric current is applied to mercury vapor inside the tube, causing it to emit ultraviolet (UV) light. A phosphor on the walls of the tube absorbs the ultraviolet light. This causes an electron to jump up to an orbital with a higher energy. When the electron drops back down to its normal orbital, the phosphor re-emits its energy as visible light.

The ballast

An electronic ballast

The ballast prevents too much electricity from flowing through the tube. It also starts the lamp with a high voltage for a split second when it is switched on. The ballast is either inside the fixture or, most commonly, in the plastic base of the bulb. If the ballast is in the bulb, the bulb is called a self-ballasted lamp. There are two types of ballasts, magnetic and electronic. Magnetic ballasts have mostly fallen out of use, as they are less efficient than electronic ballasts, they cause the bulb to flicker, and they do not start instantly. Electronic ballasts were at one time more expensive than magnetic ballasts, but now the price is about the same.


The average rated life of a CFL is 8 to 15 times longer that of incandescents.[3] CFLs typically have a rated lifespan of 6,000 to 15,000 hours, whereas incandescent lamps are usually manufactured to have a lifespan of 750 hours or 1,000 hours.[4][5][6]

The lifetime of any lamp depends on many factors, including operating voltage, manufacturing defects, exposure to voltage spikes, mechanical shock, frequency of cycling on and off, lamp orientation, and ambient operating temperature. The life of a CFL is significantly shorter if it is turned on and off frequently. In the case of a 5-minute on/off cycle the lifespan of a CFL can be reduced to "close to that of incandescent light bulbs".[7] The U.S. Energy Star program suggests that fluorescent lamps be left on when leaving a room for less than 15 minutes to avoid this problem. If the light must be switched on and off frequently, Cold cathode CFLs can be used. Cold cathode CFLs are designed for many more on/off cycles than standard CFLs.

Mercury content and recycling

The mercury inside the tube is toxic and makes these bulbs hazardous waste. The bulbs must be taken to a recycling center after they stop working. Most CFLs contain an amount of mercury smaller than the tip of a ballpoint pen. During normal use, the mercury cannot escape, although it will escape if the bulb is broken. If a single bulb breaks, it is not usually a cause for concern. It is recommended to open windows to air out the room, and to clean up broken glass with duct tape instead of a vacuum cleaner.

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