The LED promises numerous benefits. Among them: high efficiency, compact size, long service life, color control, no mercury content, and no radiated heat or ultraviolet output. It also has cool, interesting new capabilities. While general lighting products that use LEDs currently represent only an estimated 5 percent of the market for luminaires (or light fixtures), the technology does dominate new product development, and products are now available for virtually every lighting application, even troffers and high-bay lighting.
As a young technology, however, the LED presents risk as the lighting industry simply does not have a lot of experience with it yet. This is proving highly disruptive as LED manufacturers learn the lighting business and, in turn, lighting manufacturers learn about the capabilities of the LED. Adding in the design and building community creates another layer of complexity. Furthermore, the market is still influenced by poor-performing products and misleading sales claims. This is despite an overall improvement over the past five years as reflected in U.S. Department of Energy (DOE) CALiPER product testing (which independently tests commercially available products against manufacturer sales claims and other products).
So how can architects and other designers protect their clients’ investment in LED technology, when the quality products are typically priced higher than conventional lighting?
First, get to know the technology. For example, LEDs have a higher rate of lumen depreciation over time when compared to most conventional light sources, such as fluorescents. Service life, in fact, is based on light output, not mortality in a more traditional sense. Whereas most lamps fail by appearing to turn off and thus no longer produce any light, an LED could take an extremely long time to fail in that manner. There is typically no clear end-of-life mechanism—light output simply continues to fade until it is no longer economical to operate. That point of operation is called the L70 point—which means that LEDs should be replaced when they reach their 70 percent lumen maintenance point (the point of 30 percent light loss).
LEDs are friendly with conventional lighting controls, but all of the components must be specifically rated as compatible to ensure desired performance. LED light output, efficacy (lumens per watt), and service life are heavily dependent on ambient temperature. Higher interior temperatures degrade maximum light output, resulting in shorter product lifespans since LED service life is based on light output levels. As a result, designers should request samples to develop direct experience with selected products. A mock-up, including controls, is encouraged before a large field installation.
Architects and designers should know enough about lighting design to be able to evaluate a product based on its complete performance, not just on whether it saves energy. Sometimes we want LED technology evaluated on its own merits, such as the long service live, lack of ultraviolet or radiated heat emissions, resistance to shock and vibration, and ability to change color temperature. Other times, we want an LED product to deliver equivalent or better performance as compared to a conventional product.
A common set of vocabulary and performance metrics allow meaningful evaluation and comparison of products. As LEDs are a unique light source, however, previous standards were not sufficient, and the lighting industry rapidly developed several standards and accepted metrics. As discussed earlier, the L70 metric is an end-of-life formula identifying the point in time that the LED product will deliver 70 percent of its initial light output, with replacement recommended at that point. Other standards ensure products are tested to common methods and can be evaluated against one another fairly. For example, IES-LM79-2008 is a testing standard producing total light output, color, and other characteristics, and IES-LM80-2008 is a method to test lumen depreciation for LED packages, modules, and arrays (but not complete luminaires) up to 6,000 to 10,000 hours. IES-TM-21-2011 describes a procedure to extrapolate this data to estimate light output to a fixture’s end of life. A process for testing the color quality scale, a color-rendering metric better suited to LEDs than the current color rendering index, is being vetted. The standards themselves are not the focus—the product performance data based on the standards is. Specifiers should make sure the data for the LED products they are considering is based on common standards for reliable comparison.
Besides standards, the DOE and the lighting industry also have partnered to develop mechanisms that designers can use to identify quality products and quickly evaluate and compare their performance.
The Lighting Facts label (lightingfacts.com, see image above) is a voluntary program that provides basic LM79 performance data in a standard format, with products tested to verify product claims. The DOE’s Energy Star label (energystar.gov) identifies LED products that provide equivalent or superior performance to conventional products while saving energy, for a limited range of commercial and residential product categories. The DOE’s Solid-State Lighting Program (www1.eere.energy.gov/buildings/ssl/index.html) offers a number of tools, such as demonstration projects and independent product testing reports via the CALiPER product testing program). The DesignLights Consortium’s Qualified Products List (designlights.org) is used by utility companies and energy-efficiency programs as a pre-approved list for financial incentives, and covers more categories than Energy Star. Awards programs can also help identify quality products. The Next Generation Luminaires Design Competition (www.ngldc.org) recognizes high-quality commercial products on the market, and Lighting for Tomorrow (lightingfortomorrow.com) plays a similar role for residential products.
As the LED revolution continues, designers should take steps to ensure that LED is the appropriate technology for their applications, that all selected products are interoperable, and that the products deliver the highest likelihood of satisfying the project goals.
Craig DiLouie is a contributing editor to eco-structure and principal of ZING Communications (zinginc.com). He is the former editor and publisher of Architectural Lighting magazine. This is the second of a three-part series focusing on lighting. Click here to read the first installment, "Spell It Out: A Look at the Written Lighting-Control Narrative." The final installment will appear in the November/December issue.