How many candelas equals 1 lux?

Answer 1

They really aren't equal because they measure two different things. However, they are related to each other.

The Candela is the measure of the luminous intensity of a light source. A higher Candela number means a brighter light. Lux is a measurement of light density and means lumens per square meter. Again, a greater number of lux means that the surface being illuminated by the light is is receiving more light per square meter.

The formula for calculating the conversion of candelas to lux is E = I/(D*D) where E is the Illuminance of the the surface in lumens per square meter (lux), I is the Intensity of the the light source in Candelas and of course (D*D) is the square of the distance from the light source in meters.

Therefore 1 Candela will illuminate a surface with 1 Lux only at one meter from a light source. At different distances it will illuminate to different densities of light.

For example: Solving for E, that same one candela light source would only read 1/4 lux at two meters [ 1/(2*2)] and 1/16 lux at four meters [1/(4*4)].

If you know the lux at a given distance in meters from the light source you can solve for I and it will give you the intensity of the light in Candelas. From that you can calculate the intensity of the light.

For example: Solving for I, multiply the lux times the square of the distance in meters and you will have the intensity of the light source in Candelas.

So a reading of 8 lux at a distance of 3 meters would mean that the light source has an intensity of 8*3*3 or 72 candelas.