Measuring the Luminance

Modern illumiance meters incorporate an optical system trough which an object of interest is looked at. A small display in the viewfinder gives an immediate reading by the push of a button.

Such illuminance meters are very easy to use. However, they tend to be quite expensive.

A simpler way of measuring the illuminance is to use a photocell with a special shading rod. The shading device defines a solid angle of incidence. By knowing the area of the sensor and the solid angle, the illuminance can easily be derived.