L70 is a way to measure LED lifetime and is one of the most important ratings electricians, purchasing agents, and end users can use to decide which lighting fixture best suits their project. According to the United States Department of Energy, useful life (or rated life) is “often described by the number of operating hours until the LED luminaire is emitting 70 percent of its initial light output.” It is through this definition that we find the L70 rating.
Any light fixture—LED or otherwise—will slowly but surely degrade over time. Older light sources rely on the heating up of filament to create their light; once the filament wears away to the point where the fixture emits 70% of its initial lumen output, it is said to have reached the end of its life. Even though LEDs do not rely on filament, the principles behind rated life have not changed.
LEDs do not degrade nearly as quickly as other light sources, as they rely on electroluminescence rather than filament to emit their light. For this reason, it is not uncommon to see LEDs with L70 rated lifetimes of 50,000 hours, 100,000 hours, 200,000 hours, or greater.
For example, let’s imagine an LED bollard light that produces 2,100 lumens and is said to have an L70 rated life of 50,000 hours. When you first power up the LED bollard light, it should emit the full 2,100 lumens, though over time, its emitted lumens will start to fall (as they would for any other light source). However, whereas a high-pressure sodium bollard light might take 25,000 hours to hit 70% output (1,470 lumens), the LED fixture will last twice as long. The LED will still continue to operate beyond this point, but this is the point at which most people would consider replacing the unit.
How Did We Measure the Lifetimes of Older Technologies?
Prior to the introduction of light-emitting diodes (LEDs), conventional light bulbs were tested in batches of 100 with the expectation that at least half of the batch would fail prior to the end of a 10,000-hour testing mark. Traditional light bulbs, which included fluorescents, HIDs, and incandescent lights, were the standard for lighting fixtures and testing goals. A fluorescent lamp from one manufacturer would generally have the same rated life as a fluorescent lamp from another manufacturer, making the lifetime of the entire category of lighting easily predictable. Classifying the average life of a light source was a monotonous—though consistent—process. That is, until the LED came along.
Predicting the lifespan of LED luminaires is much more difficult. Unless it is damaged in some way, an LED may never truly fail—it will simply deliver less and less light until it appears to no longer be functioning. Because LEDs do not rely on the burning of filament, they will last longer and be less susceptible to flickering and inconsistent light over the course of their lifetime. While LEDs do occasionally fail, they are significantly more reliable light sources than their predecessors.
Average Rated Life: Reported and Calculated LED Lifetime
The tremendous lifetime of LEDs has brought about a new series of classifications for the average rated life of luminaires. Rather than testing for periods of 50,000, 60,000 or 100,000 hours, these luminaires are tested for 6,000 hours at three different temperatures, as required by ENERGY STAR®. This method, called TM-21, provides mathematical calculations that simulate the full length of life. The data provided from TM-21 testing is generally more conservative than actual reported lifetimes.
Predicting the Future of LED Lifetime Could Be Difficult
With the ever-evolving changes that LED lights bring to the marketplace, whether in luminaires or in other technologies, accurately predicting the future rates of lumen depreciation is challenging. Every day, manufacturers and engineers are designing new LEDs that last longer, perform better, and are more dependable than older designs. The testing processes may never catch up.
Speak to an Access Fixtures Lighting Specialist
Access Fixtures prides itself on using high-quality components to provide reliable LED lighting solutions. Whether you need LED sports lighting, LED high bays, LED bollard lights, or another kind of lighting altogether, Access Fixtures has the resources to get you the solution you’re looking for. Do you need to discuss a unique lighting project or an LED Lifetime? Talk with an Access Fixtures lighting specialist by phone at 800-468-9925 or by email at [email protected] today.