Light bulbs are measured in watts, which is how much energy they use.  A typical light fixture in your home takes a 60 watt bulb, but if it were a CFL, which is more energy efficient, you would only need 13 watts to give you the same amount of light.  This can be confusing when you just want to replace that burned out light and can’t find the same wattage on the shelves at your hardware store. 

Light bulbs can also be measured in lumens, which is the amount of light they give off, or brightness.  In the example below, the incandescent bulb gives off 820 lumens of light and uses 60 watts, whereas the CFL (on the right) gives off 870 lumens of light and uses only 13 watts.

Compact fluorescent bulbs can produce the same amount of light (lumens) as a traditional incandescent bulb, while using significantly less energy (watts).  However, current light bulb packaging only advertises watts, but in mid-2011, the packaging will be more like nutrition facts that call out lumens, the estimated yearly energy cost, lifetime expectancy and light temperature of the bulb.