Energy-efficient optionsGiven the prevalence of downlights in modern homes, potential energy savings from high-performing, energy-efficient downlights would be significant. Lighting accounts for 15–20% of household electricity use. The US Department of Energy estimates there are at least 500 million recessed downlights installed in US homes, and more than 20 million are sold each year. Both compact fluorescent lamp (CFL) and LED technology can decrease downlight wattage by 75% or more.
The high-temperature environment in recessed downlights has plagued attempts to use CFLs in this appplication, but more than a dozen reflector CFL products proven to perform well at elevated temperatures are now on the market. Recent developments in LED technology and luminaire design also look very promising, in terms of both light output and efficacy.
Comparing LED recessed downlights to traditional light sourcesAlthough originally intended for directional lighting, recessed downlights are now used widely for general ambient lighting in kitchens, hallways, bathrooms, and other areas of the home. Other types of downlights using spot lamps, reflectors, and lenses are also used for art, accent, display, and wall lighting. In some applications, like media rooms and dining areas, downlights are operated on dimming circuits. The most common light source used in residential downlights is a 65-watt incandescent reflector-style lamp with a standard Edison base. Other commonly used options include A-type incandescent lamps, and PL-type, spiral, or reflector CFLs.
The light output of a traditional recessed downlight is a function of the lumens produced by the lamp and the luminaire (fixture) efficiency. Reflector-style lamps are specially shaped and coated to emit light in a defined cone, while "A" style incandescent lamps and CFLs emit light in all directions, leading to significant light loss unless the luminaire is designed with internal reflectors. Downlights using non-reflector lamps are typically only 50% to 60% efficient, meaning about half the light produced by the lamp is wasted inside the fixture. Recently, LED downlights have come on the market. Table 1 provides examples of performance data for residential recessed downlight using several different light sources, including two LED products. These data should not be used to generalize the performance of fixture types, but are provided as examples.
* Based on photometric and lamp lumen rating data for commonly available products. Actual downlight perfor-mance depends on reflectors, trims, lamp positioning, and other factors.
** Results for two commercially-available products tested. LED 1 was tested in Aug 2006. LED 2 was tested in Sep 2007. Lamp level data are not available for the LED downlights, which contain proprietary LED arrays, heat sinks, reflectors, and diffusers.
The 13W spiral and 15W reflector CFL systems have similar luminaire efficacy and both lamp types are readily available from all of the major lamp manufacturers. Available LED products vary widely in light output and efficacy. LED 1 provides less than half the delivered light output of the 15W reflector CFL, but the newer LED 2 fixture provides more net lumens than the 15W RCFL or the 65W incandescent and has the highest overall luminaire efficacy of the options shown here.
Downlighting qualityThe table below compares three fixtures/lamping options in terms of color quality measures, luminous intensity, beam angle, and average luminance.
The downlight using an incandescent reflector flood lamp provides more light in the center of the beam (center beam candlepower) and a narrower beam than either the CFL or LED downlights. Depending on the application this may be an important consideration. But on total luminous flux, color temperature, and color rendering, both the CFL and LED products are good options.
Residential downlights are often a glare problem, as indicated by the high average luminance figures for all three of these products. For the products listed above, both the CFL and LED alternatives would be an improvement over the most common lamp type used in residential downlights, the 65-watt reflector flood, but particularly in lower ceilings, glare may be an issue. Using louvers, shielding trim, or deeper recessing of the light source alleviates glare, as does dimming. Alternatively, wall sconces, cove lights, wall washers, or torchieres may be better options for lighting the room because they diffuse light over a large surface (the wall or ceiling), while completely hiding the light source.
Related category• LIGHTING TOPICS
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