The 70% rule and LED lifespan (L70)
In contrast to incandescent bulbs that burn out and fluorescent lights that start to flicker, LEDs act differently in that they progressively lose their ability to produce light over time. Therefore, you may anticipate the LEDs on your LED strips to be functional until they are deemed too dim for usage, barring any "catastrophic" failures brought on by things like power surges or mechanical damage.
However, how dim is "too dim for use"? As for the answers, they are as varied as the uses for illumination. However, the industry has rather arbitrarily chosen that that line in the sand should be set at 30% light loss or 70% of light remaining. This measurement, often known as the L70 meter, indicates how many hours it would take an LED to produce light that was only 70% as bright as it was initially.
How is L70 determined?
The choice of materials, their strength, and their quality are only a few of the numerous variables that affect LED lifetime. However, in general, greater temperatures and higher driving currents both cause a quicker fall in light output.
Because the materials chosen by different LED kinds and manufacturers might differ greatly, a test methodology known as LM-80 was created to provide the benchmark for testing on the durability of lights. The LM-80 standard calls for testing sample specimens at preset drive currents and temperatures, with variations in light output being evaluated every 1000 hours up to 10,000 hours.
To guarantee unbiased findings, LM-80 testing are normally carried out at independent laboratories. The results are then made public in the form of reports. All respectable producers will undertake this test on their LEDs, and a respectable LED strip provider should have no trouble giving it to you, especially if you're purchasing in bulk.
LED lifetime testing is challenging since it takes a long period. Even if the LEDs are on constantly, it will take almost 14 months to complete a 10,000 hour test. In a sector like LED lighting, where things move quickly, this is a lifetime. A product would need to be tested for close to 6 years in order to meet the entire 50,000 hour promise.
As a result, the TM-21 extrapolation algorithm was created. The program outputs an expected lifespan number after analyzing the performance of the LM80 samples throughout the first few thousand hours. This figure is frequently provided on specification sheets and guarantees.
There are three reasons why your LED strip lifespan promise can be false.
For lifetime claims, the LM80 test and related TM-21 methodology contain a number of criteria and requirements. The lifespan promises made by your LED strip provider may not be accurate if they did not adhere to these guidelines.
1) The maximum amount of hours you may claim is six times what was actually tested. In other words, even if the LEDs operated faultlessly for the whole 5,000 hours of the LM80 test, the greatest lifetime you can infer from this data is 30,000 hours. This prevents hasty judgments from being made based on scant information.
2) The specifications for the LM80 tests' drive current and case temperatures must be greater than those for the LED strip's drive current and case temperatures. The main elements that impact LED lifetime are temperature and driving current, as was already explained. Your real usage circumstances may be worse than the LM80 testing if your LED strip is set up to operate at a greater driving current and is routinely used in a warm attic. The initial lifetime forecasts would be overstated as a result.
3) The LM80 and TM-21 lifetime warranty isn't flawless or error-free. LED lifetime can also be impacted by elements outside the scope of the test protocol, such as humidity or VOCs included in the waterproof LED strip potting compound. A company wishing to save money may utilize superior materials for the samples used in the LM80 tests alone and use inferior, cheaper materials for mass production because there are minimal restrictions on what materials may be swapped in an LED's construction while still applying the same LM80 test report.
Your LED strip could change colors as well as its brightness.
An LED can actually start to change in hue over the course of its life in addition to fading over time if materials deteriorate at different rates. While the magnitude of the color shift is detailed in LM80 test results, LED strip specifications hardly ever mention it. You will thus have a difficult time locating material on what level is appropriate for your application and the industry as a whole.
If you can obtain the LM80 test reports from the LED manufacturer or a measurement known as "delta u'v'," you can gain an idea of color stability by remembering that a delta u'v' over 0.003 is regarded as perceptible to the human eye. For the majority of interior lighting applications, delta u'v' ≤ 0.006 during the lifespan of the LED strip products is regarded as acceptable. However, you might want to use a device with higher color consistency over time for more demanding applications like lighting up artwork and demanding applications like museums.
