You often encounter the term Lumen when purchasing lighting. Lumen stands for the unit of luminous flux: it measures the amount of light coming from a light source.
The difference between Lumen and Lux
Lumen represents the luminous flux that lights emit. The more lumens a fixture has, the brighter the bulb. Lux says something about light. The lux value helps determine the extent to which a translucent surface is illuminated. A lamp can be very bright, but that doesn’t mean you have enough light. For example, a lamp’s beam may be too narrow, allowing only enough light under the fixture. Around that, there is not enough light. Fixtures may also be placed too far apart or the lamp is not bright enough for the height of the ceiling. So lumens only say something about the light coming out of the fixture. The lux value tells how much light is total in the room.
Lumen and Wattage
In addition to the term Lumen, you will often encounter the term Wattage. A wattage (Watt) shows how much energy a lamp uses. This is expressed in number of Lumens per Wattage. As lighting becomes more and more energy efficient, the Watt to Lumen count is also getting lower and lower: around 200 lumens per Watt.
However, the CRI value does affect the Lumen-to-Watt ratio. The higher the CRI value is, the less Lumen you need. Light sources with warm tones (<4000 Kelvin) are slightly less economical.
How many Lumens do I need in my project?
How many Lumens you need for your project depends on the NEN-EN standards described according to the European Union. The required Lumen Output depends on the height at which the lighting is hung, the required reach of the lamp and the appearance of the fixture. The number of fixtures used is also important. This is simulated in a light calculation in Dialux.