The Jolly Photometer uses two translucent paraffin blocks separated only by a sheet of opaque metal foil which one views on edge. When one places the photometer between two different light sources, the edge of each block of paraffin is a characteristically different whiteness—the brighter the light, the whiter the paraffin. If the blocks show the same color of white, then the intensities of the sources are directly proportional to the square of their distances from the opaque metal foil. The paraffin blocks and metal foil are permanently mounted in a steel housing that fits the standard meter stick. Complete with instructions.