What is the difference between Lumen, Lux and PAR?

Within the light spectrum, Lumen, Lux and PAR are one of the best-known concepts when it comes to light measurements. Yet it is important to know the difference, because the one is no substitute for the other. These are independent concepts that are extremely important in determining the light output in, for example, offices, sports locations or horticultural greenhouses with cultivation lighting.


Let us 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 time unit (for example per second). This only concerns the amount of light emitted by the lamp, whereby the direction and range are not important. The amount of lumen 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 therefore a unit for luminous flux and indicates to what extent the surface is illuminated.

This Lux value is very important at indoor sports locations and in offices. For businesses, there are even legal requirements for work lighting that it must meet.

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


A PAR meter indicates the light that flowers and plants need to achieve photosynthesis and thus measures the growth potential, as it were. PAR stands for Photosynthetically Active Radiation. Lumen and lux is used by us humans as a unit and measure for the amount of light. However, these are data that are only observable with the human eye.

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

In short, Lumen and Lux is for people and PAR is for plants and flowers. We are happy to help you accurately and reliably measure and monitor the Lux and or PAR value with one of our measuring instruments. View our range of light meters here.