When choosing any type of lighting, consider the lamp (the industry's term for light bulb):

• size and shape -- Will it fit the fixture?; 
• wattage - the amount of energy it uses;
• lumens per watt - the amount of light per watt, so its energy efficiency;
• color rendering index (CRI) - the higher the number the more true to life color quality;
• color temperature (Kelvin, or K) - higher numbers are whiter, cooler and closer to daylight; lower numbers are warmer and more similar to incandescent;
• and life expectancy. 

Another consideration is "Instant on." Some compact fluorescent lamps (CFLs) take 30-60 seconds to come up to full brightness. If this is an important issue, be prepared to pay a bit more for "Instant on" CFLs. All fluorescent lamps require a ballast to regulate the flow of electricity. A magnetic (older, heavier technology), or electronic (lighter and more energy efficient) ballast may be a separate piece, or integrated as a part of the lamp. ENERGY STAR® has more information about Compact Fluorescent Lamps/Lightbulbs. The U.S Department of Energy's Energy Savers can also provide you with more information on CFLs.

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