Illuminance is the term used to describe the amount of light or luminous flux from a light source falling on a surface and is measured at specific points on this plane. Illuminance is expressed in lux.

Indirect lighting describes the lighting distribution of a fixturewhere the emitting surface is not directed towards the work plane or surface where the visual task is executed. It is however directed towards a surface (e.g. ceiling or wall) and only the reflected or bounced lighting reaches the work plane.