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Definition of illuminance

Definition of illuminance

Illuminance - symbol E, unit lux (lx)


Definition of illuminance

Illuminance is the quantity of light, or luminous flux, falling on unit area of a surface (Fig). It is designated by the symbol E. The unit is the lux (lx). One lux equals one lumen per square metre (lm/m2 ).



 


Illuminance can be defined as:


The ratio of the luminous flux incident on a surface to the area of that surface.


 


Or


The Illuminance is independent of the direction from which the luminous flux reaches the surface.


Some practical examples:


Summer, at noon, under a cloudiness sky

100 000 lux


Ditto, but in the shade

10 000 lux


In the open under a heavily-overcast sky

5000 lux


Artificial light, in a well-lit office

1000 lux


Artificial light, average living-room

100lux


Street lighting

5-30 lux


Full moon, on a clear night

0,25 lux