The illuminationE, in foot candles,provided by a light source of intensity I,in candles,at a distanceD,in feet,iSgiven by
For an illumination of50 foot candles at a distance of 4 feet from a source,the intensity of the source must be A、50 candles B、200 candles C、800 candles D、1,600 candles E、2,500 candies