Advanced LED Education
LED Brightness: lux, lumen and watt
The power or brightness of LEDs is often defined by many terms such as watt, lumen, and lux.
This is a measure of power used by the lamp. Historically this has told us how powerful a lamp is (e.g. 60W incandescent lamp) but because there are more efficient lighting technologies out there, this is not an accurate means of calculation brightness any more. E.g. a 60 Watt incandescent bulb, 20 Watt CFL and a 10 Watt LED may all produce the same amount of light but all have different powers.
The lumen is a measurement of the total amount of visible light emitted from a light source. Not all of this light is useful and so this measurement cannot be used alone (some of the light might be behind the fixture or emitted in the wrong direction. The amount of light that hits a surface is also important. LED lumen values are often less than the lumen value of another light technology for the same amount of brightness on the surface. This is due to the directional nature of LED lamp.
This is the amount of visible light on a surface. This can be described at certain distances from the light source (i.e. 200 lux at 1 meter). It is a good way to determine the amount of “useful” light created by a light source but can also be misleading if used on its own. A lamp with a small beam angle can have a high lux level, but low overall lumen output, while a lamp with a large beam angle can have a large lumen output but a low lux level. Both need to be compromised and suited to the correct application.
When choosing an LED lamp, you may see that the lumen value listed on the LED lamp does not match that of an incandescent or halogen, but the lamps offer the same about of light on a surface. This is because the light from an LED lamp is “directional” where an incandescent light shines light in all directions: only a part of which is used to light up the surface you want.