What Is a Lux? Light Levels Explained

[Lazlo]

I have heard the word, but have very little idea as to what it represents. I know it has to do with light level. Any help would be appreciated.

 

[laurent.a]

The lux (light in Latin) is the standard international unit for lumination.

Imagine a part of a ball, 1 m radial, 1 metersquare the surface. Imagine a candle in the center of this part ball. One lux is about the total quantity of light received by the 1 m2 surface, since the unit of light intensity, the candela (candle in Latin) is about the one of a candle.

The lumination is to be regarded as the quantity of light falling on one spot or surface, from one direction (it's vectorial).

It depends: on the intensity (punctual source) or luminance (extended source) of the source

on the distance of the considered spot or surface to the source (it actually decreases with the square of the distance).

on the relative angle between both surfaces (if so) of the source and receiver.

 

[DannyG]

uuuuhhhhhh. I was never good at math.

 

[laurent.a]

I see that English/American people use more fc (footcandle) for measuring lumination. 1 fc is about 10 lux.

 

[ModellingAgencies]

The lux (symbol: lx) is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface.