What is the difference between illuminance and luminance?
Answer Illuminance (E) – Is measured at a point on a surface. It is the quotient of the luminous flux incident on an element of the surface containing the point, and the area of that element. Illuminance is measured in lux. The orientation of the surface may be defined, e.g. horizontal, vertical, hence horizontal illuminance, vertical illuminance. In plain English it is the amount of light you measure with a light-meter (photometer) at a point. In those clips you see of photographers standing by the model with their light-meter, or the umpires at a cricket match deciding on whether the light is good enough to play they are measuring illuminance. Horizontal illuminance is measured with the meter held upwards, vertical with the meter faced in a particular direction. Horizontal illuminance is almost always the one used, a couple of exceptions being lighting for a single television camera or at golf driving ranges. Luminance (L) – Is the measure of brightness with which the eye perceives a
