I have been designing and building LED lights for well over a decade. Those lights can be found from the bottom of a beautiful pool/fountain in Las Vegas, to the top of the CN Tower, and in -20° freezers, illuminating racks and racks of ice cream bars. Regardless of the lighting application – architectural or industrial highbay – I am still asked the same question that I was way back when I first started doing this: What is the real deal on LED lifetime?
First, here’s the scoop on lifetimes for traditional light sources. The lifetime rating you see on the side of the standard incandescent screw-in bulb is defined as the number of hours after which 50% of similar bulbs would have failed completely. This is sometimes called Mean Time Between Failure – MTBF. The bulb in the package has a 50% chance of failing before that time. And failing means no light output, of course. Here’s a look at lifetimes by type:
- Incandescent bulbs can range from 750 hours to 2,000 for “long-life” versions.
- Compact fluorescents (CFL) bulbs have claims of up to 10,000-hour lifetimes.
- Industrial HIF and HID lamps are approaching 20,000-hour lifetimes.
Remember that these are the time period at which they are expected to fail totally. And these lifetime ratings assume ideal conditions; rugged applications or lots of on/off cycles reduce the useful life. Then there is the issue of depreciation (reduced lumen output). The light from most of these bulbs will depreciate substantially (often more than 30%) within the first third of their lives, often causing designers to overlight spaces to compensate. This adds to both the up-front costs and lifetime energy cost of conventional lighting applications.
Now onto LEDs. When we talk about LED lifetime, we mean the period after which the LED light puts out only 70% of its original light. (Note: this is not total failure, just the point at which the system emits less light and a fundamental difference in the definition of ‘lifetime’ largely because LEDs are a fundamentally different illumination technology.) In technical parlance, this is the L70 rating and can range from 50,000 to 100,000 hours based on design and operating temperature. Even after that time period, the LED light will continue to operate for years; just not at 100%.
Figure 1: Typical light output change from for different light sources vs. operating hours. Source: http://apps1.eere.energy.gov/buildings/publications/pdfs/ssl/lifetime_white_leds.pdf
Lifetime is an important consideration — many people still recall the lingering ‘bad taste’ that CFLs left in the mouths of early adopters — so buyers want accurate information before embracing LEDs. And it is an important factor in the economics of an LED purchase. The Department of Energy has taken a leadership role in ensuring that credible vendors build and certify quality products. There’s the Energy Star program (for many categories of LEDs), the LightingFacts program (which ensures clear and accurate labeling), and their relationship with the DesignLights Consortium for listing highbay and industrial LED lighting products. And vendors are stepping up, too, to ensure that customers that adopt LED products have great experience.
At Digital Lumens, all of our products are built with quality and reliability as core design principles. Each Digital Lumens product is completely UL listed, listed on the DesignLightsConsortium’s Qualified Products List to ease rebate approval, comes with spec sheets that list L70, LM80 and all of the other relevant criteria, and has a 5-year warranty. We are committed to being one of the first vendors to adopt the DOE’s new Total Luminaire Lifetime Ratings, as well.
So, lifetime matters tremendously in LEDs because they offer unprecedented levels of energy efficiency AND exceptional lifetime, making them a natural choice for your illumination needs. LEDs have already taken over the traffic signals, cell phone and computer screen backlighting, TV, and automotive lighting, and are poised to capture general illumination over the next decade.
I urge you to learn more about what makes LEDs so compelling and be a well-informed customer. Ask lots of questions and make sure you are dealing with a reliable vendor and a quality product. The time is now to seriously consider LEDs for their bright and long life.