Light school

Description
In this document we will go through common terms regarding light to help you find the perfect light for your application.

Effect
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 face 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).

Lux
Sometimes it is not enough to know the amount of lumen a light or a light source have in order 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 meter, 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 distribute 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 meters distance give you a light image at 1 square meter, if this flashlight has 800 lumens, this will equal to 800 lux.
The light bulb that needs to illuminate 40 square meters thus have 20 lux.

Candela
Candela (cd) is the unit for brightness which describes the lights intensity (lux) in a particular direction at a specific distance. Unlike lumen that exhibit brightness in several directions.
1 candela = 1 lux at one-meter distance.
Where lux can be misleading (see image above) 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.