Compact fluorescent light bulbs, also known as CFLs, are an energy-efficient alternative to conventional incandescent bulbs. In an incandescent bulb, electric current heats a thin filament to the point that it glows. This design produces a warm, soft light, but the bulb loses most of its energy in the form of heat. In CFLs, electric current energizes argon and mercury vapor, which excites a glowing phosphor coating inside the bulb. This design loses very little energy to heat, which means it consumes much less power than an equivalent incandescent bulb.

CFL bulbs generally cost slightly more than incandescent bulbs, but they can pay for themselves in power bill savings. There is no industry standard for measuring energy efficiency, so energy savings ratings will vary from manufacturer to manufacturer. In general, a CFL will use around 75% less electricity than an incandescent bulb with the same light output, while lasting about 10 times longer. Additionally, since CFLs produce less heat, they can help you save on cooling costs.

CFLs come in a range of shapes, sizes, color temperatures, and brightness levels, making it simple to replace most incandescent bulbs with an energy-efficient CFL alternative. While the first generation of CFLs had a characteristic blue tint, newer designs do a good job recreating the warm glow of incandescent bulbs. This buying guide will explain the available CFL options, so you can feel confident you’re selecting the light bulbs that will work best for you. 

• Miniature Candelabra – A small bulb base, frequently used in chandeliers

• Candelabra – A slightly larger bulb base, used in chandeliers, light sconces and other small fixtures

• Intermediate – A bulb base between the candelabra and medium sizes, commonly used in ceiling fans

• Medium – The bulb base design for standard light bulbs, used in most lamps and overhead light fixtures

• GU24 – A two-pin base that fits fixtures with a corresponding GU24 socket. GU24 is an energy-efficient system, designed to replace the conventional, screw-type socket and base design

Lighting Controls 
Unlike standard incandescent bulbs, standard CFLs do not work with dimmer switches or 3-way lamps. However, you can find CFLs for these applications:

• Dimmable CFLs are designed to work with fixtures wired to a dimmer switch. A dimmable CFL cannot produce the same range of light levels as an incandescent bulb connected to a dimmer, however. Dimmable CFLs typically dim down to about 20% of total light output. Below that, the bulb switches off. If you want to use a CFL with a dimmer switch, make sure you choose a bulb with “dimmable” on the packaging.
  
  
• Three-way CFLs are designed to work with three-way lamps. When you progress through the lamp’s three lighting levels, the bulb steadily increases its light output.
  
  

Additionally, CFLs may not work with electronic lighting controls, such as timers and motion sensors. Check an electronic control’s product specifications to determine whether it’s designed for use with CFLs. 

Light Output & Power Consumption
Like incandescent bulbs, CFLs are rated based on light output, which is closely related to power consumption. When selecting a bulb, consider these standard ratings:

• Watts – Bulb manufacturers have traditionally used watts to represent light output, but wattage is actually a measure of power consumption, not brightness. Since CFLs consume less power, a CFL will have a much lower wattage than an incandescent bulb that produces the same amount of light. In other words, a lower wattage number indicates greater energy savings, not lower light output.

• Lumens – The standard unit of light output for bulbs is the lumen. A higher lumen number indicates a brighter bulb, and a lower lumen number indicates a dimmer bulb. A CFL and an incandescent bulb with the same lumen rating will produce the same amount of light.

• Equivalent Wattage – To make it easier to compare CFLs to incandescent bulbs, manufacturers generally provide an equivalent wattage rating for CFLs along with the lumens rating. The equivalent wattage tells you what type of incandescent bulb has the same light output as the CFL. For example, a CFL with an equivalent wattage of 60 produces the same amount of light as a 60-watt incandescent bulb.

• Lumens per watt – The standard measure of efficiency is the ratio of light output to power usage, represented as lumens per watt, or LPW. A higher LPW rating indicates greater energy efficiency and increased savings.

• Bulb Life – Bulb manufacturers typically provide an estimated bulb life for CFLs, generally listed in total hours. Quality CFLs have a bulb life rating of 10,000 hours or more. The exact bulb life for a CFL will vary depending on usage. For example, turning CFLs off and on frequently can shorten the lifespan.