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What is the difference between Lumen, Lux and PAR?

What is the difference between Lumen, Lux and PAR?

Within the light spectrum, Lumen, Lux and PAR are one of the best-known terms when it comes to light measurement. Yet it is important to know the difference, as one is not a substitute for the other. They are stand-alone terms that are hugely important when determining light output in offices, sports venues or horticultural greenhouses with grow lights, for example.


We start with the total light intensity of a source which is expressed in Lumen (lm). This is the unit for luminous flux and is measured in light quantity per unit time (e.g. per second). This therefore only concerns the amount of light emitted by the lamp, where direction and range are irrelevant. This is because the lumen quantity of this lamp always remains the same.


How much light actually reaches the surface is expressed and measured in Lux and is, as it were, the illuminance. Lux is thus a unit for luminous flux and indicates the extent to which the surface is illuminated.

At indoor sports venues and in the office, this Lux value is very important. For business, there are even legal requirements for work lighting that it must meet.

In short, Lumen thus indicates the total luminous flux emitted by a lamp and the LUX value indicates the extent to which the surface is illuminated.


A PAR meter indicates the light that flowers and plants need to achieve photosynthesis and thus measures growth potential, so to speak. PAR stands for Photosynthetically Active Radiation which means photosynthesis and active radiation in Dutch. Lumen and lux are used by us humans as units and measurements for the amount of light. However, these are data that can only be perceived by the human eye.

However, PAR meters do not measure for light that is important for humans, but rather for plants and flowers. This is because within the light spectrum there is only a certain range that can provide photosynthesis. This is 400 to 700 nanometres and it is within this spectrum that the plant's growth potential is measured. So the PAR value indicates the growth potential of the plant or flower. It is read in µmol/(m2 s-1).

So in short, Lumen and Lux is for people and PAR is for plants and flowers. We are happy to help you measure and monitor Lux and/or PAR values accurately and reliably with one of our measuring instruments. Take a look at some of our range of light meters below.