Lux and lumen are units of measurement of two different physical quantities: #lux are the unit of measurement of illuminance, while #lumen are the unit of measurement of luminous flux.
To give an idea of ​​the difference: the lumens of a lamp are constant, regardless of how close or far the different objects are illuminated, while the lux with which the objects are illuminated vary depending on whether you approach or move away from the lamp. For this reason, buying, for example, a lamp, you look at the lumens, while having to decide if there is enough light to read or to take a photograph, you look at the lux that "reach" the eye, or in the photographic lens ( the light which, reflected from the objects being observed or photographed, "travels" towards the eye or the lens). At night, while reading a book, there is enough light (lux) even using a dim light bulb (a few lumens) as long as it is very close to the book.
A flux of 1000 lumens generated by a lamp, totally concentrated on a surface of one square meter, illuminates that square meter for 1000 lux. However, the same 1000 lumens, spread over an area of ​​ten square meters, produce an illumination of only 100 lux.
The illuminance measured in lux therefore refers to the illuminated object, and not to the source. This is fundamental, because it determines how much a source is able to illuminate a body or a surface.
Sabino Coppolecchia talks about it at: www.audio-luci-store.it
00:00 start
00:15 lux and lumen
01:13 how to choose an LED headlight
01:30 how many watts?
01:50 what is LUMEN
01:58 what is LUX
04:24 an example
06:18 how to choose a led headlight
07:45 where to buy professional led headlights.