Incandescent Light Bulbs: These old-school bulbs work through the principal of incandescence — or producing light through heat. The electricity heats a filament (that little wire in the middle of the bulb) to such a temperature that it produces visible light. Incandescent bulbs are very inefficient: 90% of the electricity used is wasted as heat. While incandescents are impractical for most lighting situations, they can be a good solution for closets, unheated garages and outdoor lights during the winter.
Compact Fluorescent Light Bulbs: There are two parts to a compact fluorescent light, or CFL: the bulb, which contains about 3 milligrams of mercury vapor, and the ballast. The ballast contains electronic components that produce an electric current, causing the vapor to emit ultraviolet light. The UV light excites a coating on the inside of the bulb, which produces visible light. CFLs come in a range of applications and colors, and they use 75% less electricity and last 7–20 times longer than incandescents. Once they finally burn out they do need to be recycled, which you can do for free at Menards, Home Depot, IKEA and most local hardware stores!
Light Emitting Diodes: Unlike CFLs, LEDs are a “solid state” lighting technology, meaning they don’t use mercury gas. They produce electroluminescence using a diode, which is a type of semiconductor. Basically, LEDs are to incandescents what microwave ovens are to open fires: same result, different level of sophistication. LED lights use almost 10 times less energy than incandescents and half the electricity of CFLs. LEDs are great to use as holiday lights, flashlights, night-lights and under-counter lighting, but there are still some drawbacks. Most notably, the price: you can currently pay up to 10 times more for an LED than a CFL that produces the same light. In the next three years, however, we can expect this mercury-free option to rise in quality and come down in price, making it an even more practical way to light your home efficiently.