You are here

What Does That L70 Rating Really Mean?

L70 Rating

When purchasing LED products, one of the attributes customers often compare is the L70 rating. This seems reasonable since the L70 gives us a good idea of how many hours of useful life we should expect from the light source before it depreciates below 70 percent of its original lumens.  All light sources will depreciate over time, so of course you should choose the one with the highest L70 rating, right? Maybe not.  

There are several things to consider when evaluating LED lighting. First, you should understand how the L70 rating was derived, which is a lot easier now that there are IESNA-approved standards for determining lumen maintenance. 

What are these new standards? LM-80 ensures that LED manufacturers are testing for lumen maintenance in a consistent manner, for at least 6,000 hours at three different temperatures. The new generation of LED technology has not been tested for 50,000 or 60,000 or 100,000 hours, so that’s where TM-21 comes in. TM-21 provides mathematical rules for extrapolating the LM-80 data curves. Before TM-21, each manufacturer used their own formulas for calculating L70 ratings. 

L70 May Be Listed As Reported Or Calculated

If all manufacturers calculate L70 consistently, why isn’t this a reasonable way to compare LEDs?  Unfortunately there are inconsistencies with how L70 results are listed on marketing materials. The discrepancy occurs because there are two ways L70 may be listed: Reported or Calculated. 

Reported L70 values have an upper limit of 6-times the number of LM-80 test hours. Calculated is just that, a calculation based on LM-80 data. Generally, Reported is a more conservative number than Calculated, so it is important to know which of these L70 results is being presented to you.  At US Energy Sciences, we generally share the Reported L70. 
Know At What Temperature Your LED Was Tested

It is helpful to know at what temperature the LED was tested.  LM-80 requires manufacturers to test at 55ºC, 85ºC and a temperature determined by the manufacturer. Since LEDs perform better in cooler environments, check the TM-21 data to ensure you are comparing L70 ratings for products tested at similar temperatures. 

Understand Other Variables

Understand that other variables, including fixture design and heat dissipation will affect LED life. Our all-aluminum fixtures with Cool Guard™ System maximize heat dissipation to extend the life of the LED. 

LED lighting is a significant investment.  Don’t be afraid to ask us, or our competitors, for TM-21, and other associated reports on the products you are considering so that you make informed purchasing decisions.