Digging Deeper:
Flipping the Switch to Compact Fluorescent Bulbs

The Question
I understand that the new compact fluorescent light bulbs are more efficient than the “old-fashioned” kind of light bulb, but they are also more expensive. Is it true that they really last longer? Are they worth the extra money?

The Explanation
Incandescent light bulbs work by sending electricity through a thin tungsten filament inside the bulb. The filament is heated up to a very high temperature so that it emits light. Most of the energy is emitted as heat while about 10 percent is actually used as light.

A compact fluorescent lamp, or CFL, operates differently – and more efficiently. Inside a CFL are glass tubes that contain mercury. Electricity heats up the mercury, which releases light photons in the ultraviolet (UV) wavelength, which is invisible to the naked eye. The inside of a CFL is coated with phosphor, which gives off visible light when it comes into contact with the UV light photons. The CFL produces less heat than an incandescent, which makes it preferable for situations in which high heat should be avoided.

There are some situations in which a CFL cannot be substituted for an incandescent bulb, or will not perform optimally. Currently, CFLs are not compatible with timers or photocells. Extreme temperatures, high humidity, and nearby vibrations will shorten the lifespan of the average CFL. There are special bulbs designed for use with dimmers and three-way lights. A CFL should remain on for at least 15 minutes for peak performance.

The quality of light produced by CFLs is similar to that of incandescent bulbs. To make sure you’re getting comparable light, buy CFLs with lumen levels similar to the incandescent bulbs you’d usually buy.  Also, pick the right shade: bulbs can produce anything from a yellow-ish “warm” light or a blue-ish “cool” light.  Warm light is from lower correlated color temperatures while cooler light is from a higher correlated color temperature. 


Life-Cycle Analysis

Using it
You would have to buy 10 incandescent light bulbs to get the same number of hours of light as from one CFL. Also, a CFL uses about one quarter the energy of an incandescent to produce the same amount of light. This results in lower energy use, and a related reduction in carbon dioxide and mercury emissions from the generation of electricity. 

Each CFL contains a tiny amount of mercury – just enough to cover the tip of a ballpoint pen – so they cannot be tossed in your regular trash. Some retail stores that sell CFLs will dispose of them properly if you take them back to the store. Your local Hazardous Household Waste facility will also take CFLs, but may ask you to provide proof of residency. The Environmental Protection Agency lists places where you can dispose of your CFLs at: http://www.EPA.gov/bulbrecycling.  If a CFL breaks, you can find instructions for safe cleanup at: http://www.EnergyStar.gov/ia/partners/promotions/change_light/downloads/Fact_Sheet_Mercury.pdf



The Cost

From an economic standpoint, compact fluorescent light bulbs (CFLs) are a better choice than incandescent light bulbs. While CFLs are initially more expensive, the savings are seen in usage and life span. A CFL uses one quarter the watt energy of an incandescent light bulb, but emits the same amount of light. Also, the CFL lasts about 10 times longer than the incandescent. This means you only have to buy one CFL instead of 10 incandescent bulbs to get the same number of hours of lighting.

Using lifetime cost assumptions from an Energy Star CFL residential savings calculator, the table below compares two bulbs that produce similar levels of light. The total investment in a CFL is about a quarter of what is needed to use incandescent light bulbs for the same number of hours. Wattage usage and the replacement bulbs (the purchase of 10 incandescent light bulbs to equal the life of one CFL is factored into the total cost in the table below) increase the cost.

Comparison of Incandescent to Compact Fluorescent Light Bulb



Compact Fluorescent

Initial cost per bulb



Watt usage



Single bulb lifetime

1,000 hours

10,000 hours

Energy cost per kwH (1,000 hours)



Total cost for 10,000 hours
(including replacement bulbs)



Many CFLs, especially Energy Star qualified ones, have warranties, so if the bulb burns out early, the manufacturer can be contacted for a refund or replacement. There is no such guarantee for incandescent light bulbs.

CFL light bulbs come in several different shapes, including spirals, tubes and reflectors, and can be bare or covered by a glass dome.  Click here for a chart by Energy Star that can help you choose the right bulb for each light fixture.

Navigating the Rules/Public Policy
Since mercury is a hazardous waste, your used bulbs should be taken to a Household Hazardous Waste disposal site, or recycled through the store where you purchased them.

For More Information

The following U.S. government website provides more information on CFLs: http://www.EnergyStar.gov/

The costs per bulb and lifetime estimates were taken from www.1000bulbs.com. The incandescent was the 100 watt Sylvania model #12750 and the fluorescent was the Energy Star approved MegaLight model #M28023-41. Bulb costs were taken at the most expensive rate as if purchasing only one.

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