This omnidirectional photometer is intended for the measurement of daylight under grass swards; but the principle used in the instrument can be applied to measure the mean illumination at a point in other cases, for example, interior illumination. It consists of 2 small circular barrier layer cells, insulated from one another and mounted back to back, each being surmounted by a translucent diffusing hemispherical shell, diam. 5/8 in. The cell sensitivities are adjusted electrically to equality, the combined output being read on an indicator meter. Even for collimated light the response is uniform with orientation to better than [plus or minus] 5%.