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Light School

Perhaps you’ve heard some terms such as lumen and lux but would like a more detailed explanation? Find below a library of industry terms and jargons, which we will grow over time.


Effect is a measurement for how much energy a light source or any other electrical equipment consumes. This is indicated in Watt (W). The LED-technology has become very popular due to the fact that the effect is low and thereby energy efficient.

Flux (lumen)

The most common concept when talking about light is lumen (lm). Lumen is the total amount of energy that is converted to light that can be perceived by the eye.

When discussing light and its power, lumen is mostly mentioned. For older light bulbs and traditional light there were more focus on the effect (Watt).


Sometimes it is not enough to know the amount of lumen a light or a light source has to determine that it is the correct light you are looking for. An important concept, especially when discussing directed warning light, is lux.

Lux is the amount of lumen per square metre, thus the intensity on the surface the light hits. For working light or directed warning light, this concept is important to focus on.

A traditional light bulb that distributes light in all directions has a lower lux than, for example, a flashlight with the same amount of lumen. The flashlight that on a few metres distance give you a light image at 1 square metre, if this flashlight has 800 lumens, this will equal to 800 lux.

The light bulb that needs to illuminate 40 square metres thus have 20 lux.


Candela (cd) is the unit for brightness which describes the light intensity (lux) in a particular direction at a specific distance. Unlike lumen that exhibit brightness in several directions.

1 candela = 1 lux at one-metre distance.

Where lux can be misleading depending on how close to the surface the light shines.

Fun fact: Candela comes from Latin and is translated to candle. Candela was the brightness for a candle.