Candle Power

—The standard candle, by which all lights are measured, is legally held to be a sperm candle consuming 120 grains of wax per hour. The lights are compared in a photometer while a test is being made. In practical measurements, standardized incandescent lamps are more reliable and accurate than the primary standard. The standard unit of candle power established by the National Bureau of Standards at Washington equals 43° of the Hefner unit under Reichsanstalt standard condition. According to experiments made by the Government of the United States, a 1 candle power white light is visible at a distance a little more than a mile, one of 3 candle power is visible at two miles; on an exceptionally clear night a white light of 3.2 candle power was readily distinguished at three miles; one of 5.6 candle power at four miles, and one of 12.2 candle power at five miles; a green or red 2 candle power light was visible at one mile, 15 candle power at two miles, 51 candle power at three miles and 106 candle power at four miles. See also international candle.