Measurement of light intensity: Footcandle meter.

Measurement of light intensity: Foot-candle meter. The Weston Foot-Candle Meter has a photoelectric cell, a filter, and a meter designed to provide a correct measurement of visual illumination. There are three meter settings, and directions for using the device inside the flip-top lid. The foot-candle is a British unit of luminosity, for measuring luminous intensity of light in the visible spectrum. It is defined as one candela (cd) at a distance of one foot. 1 cd = 1 lumens/sr, where sr is a unit solid angle or steradian. A lumen is a quantity of luminous flux. 1 lumen (lm) is the brightness of 1/60 square cm of platinum surface at its melting temperature of 1770 deg C, which is equivalent to 1/621 watts of 550 nm light. Ref.: Physics For Scientists & Engineers,-Giancoli,2nd Ed., p.798-799