THE lowering of the cost of the electric light during the last twenty-five years, mainly due to scientific research and improved engineering methods, is fully appreciated by few. In 1910, carbon filament lamps, which had held the foremost place since the inception of the incandescent lamp, were rapidly being replaced by tantalum and tungsten lamps giving almost twice as much light for the same electric power. In the same year, by means of the new ‘squirted’ filament lamp, the light-giving efficiency was more than doubled. In 1912 the drawn tungsten filament nearly trebled the efficiency. All these lamps were vacuum lamps. In 1916 the invention of the gas-filled lamp trebled the efficiency, and the latest type of gas-filled lamp, the ‘coiled coil’ lamp, has nearly quadrupled the light efficiency, giving 11-25 lumens (approximately 0·9 candle) per watt. Many consumers are now getting their electric light at a cost of 0·5d. per unit who had to pay Qd. or more per unit in 1910. Electrical engineers and scientific workers may well be proud of lowering the cost to one fiftieth of what it was in 1910.