Light output Raw lumens v's Effective lumens

 
Hi There Jason from Offroad Scene again.

We've had a lot of queries lately on "how much lumens do your lights put out" so I wanted to explain the situation with light output some more.

Often when retailers quote light output of a product in lumens they fail to mention the quoted number is actually the Raw Lumens (or Theoretical Lumens), as opposed to the Effective Lumens. Raw Lumens is a theoretical number rather than the actual measure of light output itself, and is calculated by simply multiplying the number of LED’s on the light by their maximum output rating.   For example, if a light uses 20 LED’s each with a maximum output rating of 50 lumens, the raw or theoretical output would be 1000 lumens (20x50=1000), and no laboratory photometric testing is required to come up with this number. The problem with the raw or theoretical output is that it doesn’t take into account factors out in the real world that can decrease the light output considerably.

Like all lamps, LED’s suffer light quality loses due to several factors. The three main reasons being

• Quality of the LED light components and the manufacturing process, such as the diodes and dye
• Optical Losses
• Thermal Losses

Quality of the LED light components and the manufacturing:It is important to purchase a product that is using a quality manufactured chip.  However, as important is the actual “packaging” of the chip set.  You can have a high quality chip but if the packaging is second rate so will the end result in terms of light output and longevity of the product. In general terms “packaging” refers to the process of selecting and combining the lens, substrate, electrodes and encapsulation resin of the LED. In some instances packaging can amount to 50% of the cost of the product, so has a large impact on the end pricing point. 

Quality & manufacturing lossesThe optical clarity of the lens will dictate the loss of light intensity as it passes through the lens and the surrounding air. There are studies that show this loss can be as much as 10 - 20%.

Thermal loss:There is a common misconception that LED’s produce no heat.  They produce little if any heat in front of the light source.  They do however produce considerable heat at the rear of the diode.  Thus the reason for the heat sink built into the back of the work lights and LED light bars. If the heat produced by the diode is not dissipated away from the diode, the longevity and the light performance will be greatly diminished.
 Calculating the difference between Raw and Effective lumens:The Raw Lumen output is calculated by simply multiplying the number of LEDs in a lamp and their rated output.

Example: Raw Lumen output of 20 LEDs rated at 50 Lumens per watt is 24 x 50 = 1000 Lumen
Effective Lumen output is calculated by taking the Raw Lumen value and subtracting the Thermal, Optical and Manufacturing Losses.
Example: If thermal, optical and material loses for say 40% the effective lumen output in the above example would be 1000 Raw Lumens 40% loses = 600 effective lumens.
 In summary: You will never achieve the same amount on light out in the real world as what the raw lumen number indicates, and this is why the raw number is so subjective as it in no way indicates the light output quality from one light to the next. To effectively compare light output between light you need to compare the Effective Lumens

Well that wraps it up for this post

Jason
"Be seen be heard"
Offroad Scene