Difference between Lumen and Lux
When purchasing a lamp, it is nice to know how much light the lamp is giving out exactly. Sometimes this is indicated in Lumen and sometimes in Lux. What do these values mean and what's the difference?
Lumen is the unit of the light current. This indicates the total amount of light emitted by the light source, no matter what direction it is. In Lumen, efficiency is especially important because it indicates how efficient the light source converts power into light. This is called the Lumen / Watts ratio (Lm / W). With LED lights this value is much higher because they need less power to generate a particular Lumen current.
Lux is used to measure the amount of light output in a given area - one lux is equal to one lumen per square meter. It enables us to measure the total "amount" of visible light present and the intensity of the illumination on a surface. Thus, it is important in what direction the light source shines. This value is irrespective of the number of light sources it uses, the colour or the structure where the light shines. If the amount of Lux is indicated by a lamp, it is usually in the centre of the beam where the light intensity is highest.
The difference between lumen and lux is that the lux takes into account the area over which the luminous flux (lumens) is spread. A flux of 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 Lux.
A 500 Lumen light source illuminates 1 square meter with 500 Lux. The same light source that needs to illuminate 10 square meters, which illuminates this area with only 50 Lux.