Material lossesLED lamp output values (Lumens) can vary dramatically depending on which values are being quoted. The following information may assist selecting the right product for the right application.

RAW vs Effective Light Output
There are inherent losses associated with any lamp (LED, Halogen, HID or Incandescent).

The main losses are related to 3 items: Thermal Losses, Optical Losses and Assembly variation.

Thermal Losses:
The greatest challenge is Thermal management of LED's. LED Manufacturers typically measure the light produced by their LEDs after 25 milliseconds (ms). That is equivalent to a flash bulb. It gives a lumen number that is the absolute maximum value. However, LEDs produce less light as they get hotter. LEDs generate a tremendous amount of power in a relatively smaller area.

As the LEDs are powered for longer and longer periods of time, they typically get hotter and hotter depending on the thermal management system. It's not unusual for LEDs to get over 100ºC. For vehicle applications, most specifications require that the lamp be measured at 10 minutes and 30 minutes to make sure that the LEDs temperature has stabilized.

This will result in the LED producing 10 - 20% less light than it's advertised value.

Raw lumensOptical & Assembly Losses:
As light travels though an object (Lens), it loses intensity depending on the clarity of the lens material. This is due to inherent losses internal to the material and to losses at the boundary of the part as the light travels from air through the lens and back to air. These losses are present whether the light source is an LED or bulb. The losses associated with the lens material and optics again can vary from 10 - 20%. There are also losses associated with assembly and manufacturing variation. The LEDs output varies as the assembly tolerances may diminish the overall performance from the lamp from theoretically LED maximums.

Simply adding the expected values of the LED light sources together will never result in a lamp that shines that amount of light on the ground.

Thermal lossesRAW
The RAW lumen output is calculated by simply taking the number of LED's In a lamp and multiplying by the LED rated output.
Example: 8 LED's rated at 100 lumen per watt
8 x 100 = 800 Lumen

The effective lumen output is calculated by taking the RAW lumen value and subtracting the Thermal, Optical and assembly losses.
RAW Lumens = 800
Less - Thermal, Optical & Assembly Losses = 40%
Effective Lumens = 480 Lumens