How long LEDs last and the 70% rule
The way LEDs work is different from how incandescent bulbs and fluorescent lamps work. Over time, LEDs lose their light power slowly but surely. You can expect the LEDs on your LED strips to work until they are too dim to use, unless they fail in a "catastrophic" way due to things like power spikes or mechanical damage.
But how dim does "too dim for use" mean? The number of answers is the same as the number of lighting uses. But the business world has chosen, rather randomly, that 30% light loss, or 70% of light left, is the line in the sand. It stands for the number of hours it would take for an LED to lose 70% of its original light output. This is also known as the L70 measure.
How do you figure out L70?
Many things affect how long an LED lasts, such as the materials used, how durable they are, and how good they are. As a general rule, though, both higher temps and higher drive currents cause light output to drop more quickly.
Because different types of LEDs and makers use different materials, LM-80 was created as the main standard for tests that measure how long lights last. The LM-80 tells you to test sample materials at certain temperatures and drive currents, and it keeps track of changes in light output every 1000 hours for up to 10,000 hours.
LM-80 tests are usually done at independent labs to get objective results, and the results are made public in the form of a report. All reputable LED makers will have this test done on their products, and a reputable LED strip seller shouldn't have any trouble giving it to you, especially if you are buying in bulk.
Testing how long LEDs last is hard because it takes a long time. A 10,000-hour test takes about 14 months, even if the LEDs are on all the time. In a field that changes quickly like LED lights, this is a very long time. For a product to be tested for the full 50,000 hours, it would have to be tested nonstop for almost 6 years.
Because of this, TM-21, an extension program, was made. The program figures out how long the LM80 will last by looking at how well it worked for the first few thousand hours. This is the number that is usually written on warranty forms and standard sheets.
3 reasons why your LED strip lifetime claim may be inaccurate
For lifetime claims, the LM80 test and the TM-21 method that goes with it have a number of conditions and needs. If the company that sold you the LED strip didn't follow these steps, their promises of a lifetime warranty may not be true.
1) You can only get up to six times the number of hours that were tried. This means that if the LM80 test only lasted 5,000 hours, then the longest term you can claim for the LEDs is 30,000 hours, even if they worked perfectly. This is to make sure that people don't jump to assumptions based on too little information.
2) For the LM80 tests, the drive current and case temperature must be higher than those used for the LED strip. As was already said, temperature and drive power are the main things that affect how long an LED lasts. If you often use your LED strip in a hot attic and set it up to run at a higher drive current, your real-world use conditions may be worse than the LM80 tests. Because of this, the original estimates of the lifetime would be too high.
3) The lifetime promise for LM80 and TM-21 is not perfect and can't be broken. Other things that aren't part of the test method, like dampness or volatile organic compounds (VOCs) in the potting solution for waterproof LED strips, can also shorten the life of an LED. Also, there aren't many rules about what materials can be used instead of others in an LED's construction and still get the same LM80 test report. This means that a company that wants to save money could use better materials for the LM80 test samples but cheaper, weaker materials for mass production.
It's not just getting less bright; the colour of your LED strip may also change!
An LED may dim over time, and if different materials break down at different rates, it may also start to change colour over time. In LM80 test results, the amount of colour change is shown, but this isn't always listed in LED strip specs. In the same way, it will be hard to find information about what amount is okay for your product and the industry as a whole.
Either the LM80 test results from the LED maker or a number called "delta u'v'" can help you figure out how stable the colours are. A delta u'v' over 0.003 is thought to be visible to the human eye. Most of the time, delta u'v' less than 0.006 over the lifetime of an LED strip product is fine for most home lighting uses. For more demanding uses, like museums and lighting up art, you might want to choose a product that keeps its colour better over time.
How long an LED strip lasts isn't just about the LEDs
Most of the talk about the lifespan of LED strips is about how long the LEDs last, but the glue and power source are just as likely to fail, and when they do, they fail very badly.
Some things in the environment, like dust, humidity, and sunshine, can damage the sticky backing on the LED strip. Over time, this can cause the LED strip to come off of the surface it was placed on.
