Main Entry: ¹pho·tom·e·ter

Pronunciation: \fō-ˈtäm-ət-ər\

Function: noun

: an instrument for measuring the intensity of light, luminous flux, illumination or brightness by comparison of two unequal lights from different sources usually by reducing the illumination of one (as by varying the distance of the source or using a polarizing device) until the two lights appear equal with the amount of adjustment serving as the basis of comparison and the equality of illumination being judged by various means