The area density of the luminous flux incident at a point on a surface. The metric unit of illuminance is lux, which is the number of lumens per square meter. Another unit is the foot candle, which is the number of lumens per square foot.
A light-sensing, solid-state device with an output signal corresponding to the amount of light incident to (falling on) the measurement surface of the device. This meter should be cosine-corrected and color-corrected to better match the human visual response.