Principle of Measurement of Photometer

Principle of Measurement of Photometer Points : Principle of Measurement of Photometer The principle of measurement of most of the methods is based upon the “Inverse Square Law”.

The standard source, whose candle power is known (say S) and the source under test, whose candle power is to be determined, are set on the bench at a distance apart with some type of screen in line with.

The photometer head or screen is moved in between the two fixed sources until the illumination on both sides of the screen is same. If the distances of the standard source “S” and source under Lest “T’ from photometer head are I_i and I₂ respectively then according to Inverse Square Law.