Example of evaluation of measurement uncertainty

The operator assembles the standard lamp on one end of the bench. The luxmeter is fixed on a moveable base that can be run along the metallic rail. The operator notes down the distance D that separates the lamp from the luxmeter along with the illumination value E LU displayed by the luxmeter. The variation of the illumination level is obtained from the variation of distance D. Repeat the operation five times .

First, the uncertainty is evaluated for the reference illumination E. This illumination is determined applying Bouguer's law. For a source considered as punctual, of intensity IL située à la and at a distance D from the luxmeter, we can say that: