Why we use Effective Lumen instead of Raw
With any type of lamp (eg.LED, Halogen, HID or Incandescent) there are losses of light quality due to these three main reasons:
- Thermal Loss
- Optical Loss
- and variations in manufacturing material & processes.
Most LED manufacturers will typically measure the light produced by their LEDs after 25 milliseconds(ms), in other words as soon as the switch is turned on. The result is very similar to the flash on a camera. This number is known as the RAW lumen based on its maximum value. The LED however will lose light penetration the hotter they get( ie. the longer they're on). Because of the low power draw of an LED nowadays, they are being left on for longer therefore getting hotter and hotter dependant upon how the thermal temperature is managed.
Automotive applications should specify that the measurements of light output be done between 10 and 20 minute intervals so that the temperature has stabilized. This normally relates to a 10 - 20% reduction in light output from an LED from a RAW specification.
Optical & Manufacturing Losses:
Depending on the clarity of a lens, light will lose intensity as it passes through the lens. Loss of light also occurs as the light passes through air, the lens and then to the atmosphere outside of the lamp. Again as above, the loss can vary anywhere between 10 - 20%. Loss can also occur based on the materials used in manufacturing and the process of manufacturing itself.
To clarify, you will never obtain the same amount of light on the ground from what are the theoretical RAW maximum of the LED's.
Calculating the difference between Raw and Effective
The Raw Lumen output is calculated by simply multiplying the number of LEDs in a lamp and and their rated output.
24 LEDs rated at 100 Lumens per watt> 24 x 100 = 2400 Lumen
The Effective Lumen output is calculated by taking the Raw Lumen value and subtracting the Thermal, Optical and Manufacturing Losses.
Raw Lumens = 2400
Less - Thermal, Optical & Assembly Losses = 40%
Effective Lumens = 1440 Lumens