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Can I use a CFL with a dimmer switch?  Follow

The short answer is: yes, certain ENERGY STAR certified CFLs are made to work on dimmers. Be sure to check the fine print on the back of the packaging for the proper applications to see if there are any restrictions on the product's use.

Dimming an ENERGY STAR qualified CFL that is not designed to work with a dimmer switch can shorten its life significantly. To find a list of dimmable CFLs, visit the ENERGY STAR CFL Advance Search and search on "Dimmable CFL." Your local hardware store may not stock a wide variety of dimmable CFLs, so if you are looking for a specific wattage or bulb type, you may want to try to purchase it online. The ENERGY STAR Store Locator lists local and online retailers who sell CFLs.

The longer answer is: CFL ballasts are designed for a specific input voltage and are not designed to handle changes in input voltage, and imposing them can cause the circuitry to malfunction or not be able to effectively light the lamp or keep the current through the lamp well regulated. This can significantly shorten the lifespan of the product. Newer dimmers are actually semiconductor devices that turn the switch on and off very rapidly - 120 times per second in normal designs. Because CFLs have a finite start-up time, and because frequent switching shortens bulb lifetime, these switches prevent the CFL from working optimally, and cause it to burn out quickly. Manufacturers compensate for these problems by designing the power electronics within the ballast to deal with these issues. This requires more complicated and more expensive parts. Alternatively, you can design a special dimming switch for CFLs that put those power electronics before the switch rather than after it. This is more expensive, however, and requires a bigger retrofit. Even with this "fix" there are expectations for dimmable products that need to be addressed. First, dimmers can dim an incandescent from 100%-0% of the total light output smoothly and continuously. Even for those who have the appropriate power electronics, CFLs are not able to dim to 0%. Most dimmable CFLs can only dim to somewhere between 10 and 20% of initial light output. Second, as incandescent bulbs dim, the color of the bulbs gets "warmer," that is, the correlated color temperature drops. As CFLs dim, their color temperature remains constant. Because of this phenomenon (known as "amber shift"), many consumers who do use dimmable CFLs do not get the ambiance they are hoping for.

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