What is lighting efficiency?

Lighting efficiency is usually expressed in lumens per watt (lumen = about 1 candle). Edison's light bulb produced about 0.6 lumens per watt. A modern 60-watt incandescent bulb produces 14.8 lumens per watt. A 13-watt twin tube fluorescent produces 56.3 lumens per watt. How much do I save using a compact fluorescent light? Changing incandescent to compact fluorescent lighting benefits everyone. A compact fluorescent light using 16 watts of energy replaces a 60-watt incandescent bulb. The life of this bulb is 10,000 hours or approximately 10 times longer than an incandescent bulb, saving $35 worth of energy over the life of the bulb. This eliminates the emission of 1300 pounds of carbon dioxide and 26 pounds of sulfur dioxide from a coal fired plant producing electricity. Considering 10 incandescent bulbs would have to be replaced at an average cost of 50 cents, the typical net savings using compact fluorescents would be $25 per bulb. The logic and economics in environmental savings are difficult to ignore. (Cook)