CFLs produce light differently than incandescent bulbs. In an incandescent, electric current runs through a wire filament and heats the filament until it starts to glow. In a CFL, an electric current is driven through a tube containing argon and a small amount of mercury vapor. This generates invisible ultraviolet light that excites a fluorescent coating (called phosphor) on the inside of the tube, which then emits visible light.
CFLs need a little more energy when they are first turned on, but once the electricity starts moving, CFLs use about 70% less energy than incandescent bulbs. A CFL’s ballast helps "kick start" the CFL and then regulates the current once the electricity starts flowing.
This entire process typically takes 30 seconds to 3 minutes to complete, which is why CFLs take longer than other lights to become fully lit. CFLs with decorative covers like globe or reflector shapes have a unique design challenge that results in the tradeoff of a slower warm up time, which is why these CFLs take longer than bare spirals to reach full brightness.
Older CFLs used large and heavy magnetic ballasts that caused a buzzing noise in some bulbs. Most CFLs today — and all ENERGY STAR certified CFLs — use electronic ballasts, which do not buzz or hum.
- Look for the ENERGY STAR label
- Decide how much light you need
- Remember that Lumens measure brightness, not Watts
- Learn more about brightness.
- Check the package for the bulb’s recommended use
- New bulbs are specially designed for certain applications, let the package be your guide!
- Check out our Guide to ENERGY STAR packaging
- Think about the mood you want from your light
Check out the ENERGY STAR Light Bulb Purchasing Guide (PDF, 1.49 MB)