Inverse Square Law

2-1-065

A formula relating the illuminance (E) produced on a plane surface element at a given distance (x) from a light source to the luminous intensity (I?1) of the source in the direction of the element. If the normal to the element makes an angle ?2 with the direction of the incident light, the law may be expressed as

(Equation)

In this form, the cosine law of illuminance is also expressed.

Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)

English