CFL light bulb

Figure 1. A CFL light bulb and the parts it contains.[1]

Compact fluorescent light bulbs (CFLs) are a type of light bulb used for lighting needs in a wide range of applications. They are much more energy efficient than incandescent light bulbs which are currently still in wide use. Many countries are however trying to phase out the use of incandescent light bulbs because of their poor use of electricity, and are moving towards the use of CFLs and LED light bulbs instead.[2]

CFLs use about a quarter of the power that a typical incandescent bulb does. This means that a 13 watt bulb (a watt is a unit of power) produces the same high-quality light as a 60 watt incandescent.[2] These bulbs have the same brightness of 800 lumens, therefore the CFL bulb accomplishes the same goal while using less power.[2][3]

CFLs take longer to heat up compared to other bulbs, however. Their start-up requires slightly more energy, but once running at a constant rate they are quite efficient with their energy use.


CFLs are safe and must meet proper guidelines to avoid fire and shock hazards.[2] They do contain a small amount of mercury, which can be a pollutant if disposed of improperly. Therefore CFLs should not be thrown in the trash, as there are most often designated recycling locations for a burnt out bulb. If a CFL is broken, there are proper guidelines to ensure safety; these can be seen here (EPA).

How they work

A CFL light bulb works differently from an incandescent or halogen bulb. Incandescents and halogens work by passing an electric current through a filament, which in turn heats up and produces light. CFLs instead send electric current through a tube (Figure 1) filled mostly with argon gas, and a slight amount of mercury gas. These gases generate ultraviolet light, which excites atoms on the phosphorous coating of the tube, which in turn emits visible light.[1]

As mentioned above, CFLs take longer to start-up because the gases within the tubes must be at a high enough temperature. The ballast (Figure 1) helps to kickstart this heating by pulling more power from the outlet. Once the gases are sufficiently hot, which takes anywhere from 30 seconds to 3 minutes, the ballast regulates the bulb to lower power, and maintains high efficiency.[1]

For Further Reading

For further information please see the related pages below:


  1. 1.0 1.1 1.2 Energy Star. (Accessed Sept 3, 2015). Learn about CFLs [Online], Available:
  2. 2.0 2.1 2.2 2.3 Natural Resources Canada. (Accessed Sept 3, 2015). Facts About Compact Fluorescent Light Bulbs [Online], Available:
  3. Energy Star. (Accessed Sept 4, 2015). Learn about brightness [Online], Available:

Authors and Editors

Jordan Hanania, Jason Donev
Last updated: May 11, 2018
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