Typical light-bulb packages usually describe the bulb in terms of lumens and watts. Both figures are important in deciding which bulb to purchase.
Lumens - A lumen is a measurement of light brightness. Technically, a lumen is the amount of light emitted through an angle called a steradian by a source with the intensity of one wax candle, radiating uniformly in all directions.
Efficiency - For example, compact fluorescent light bulbs, using fewer watts, can provide the same amount of lumens as an incandescent light bulb.