The incandescent light bulb has virtually disappeared from the modern office building. Energy-efficient T8 lamps with electronic ballasts, compact-fluorescent lamps and light-emitting-diode exit signs and task lighting have become standard practice in new buildings and most lighting retrofits. Increased use has brought scrutiny about lamp versatility; color quality; and potentially hazardous components, such as mercury. In addition, these lighting advancements are growing at a slow pace beyond the commercial market. With green-building practitioners increasingly focused on life-cycle costs, lighting manufacturers will need to design products that unlock the technologies’ full savings potential. With a little education about CFLs and LEDs, however, today’s green-building practitioners already can expect to achieve energy savings far beyond the reach of the incandescent bulb.
As green-building practices mature, increased attention is paid to extracting incremental savings from newer technologies. Lighting is at the forefront of this initiative because it is the single highest energy end-use across commercial buildings; estimates range from 25 to 40 percent of total energy use. Utilities’ energy-efficiency programs and cost-conscious building owners have taken notice and targeted lighting to achieve savings. Past technological improvements, including switching from magnetic ballasts to higher frequency electronic ballasts, resulted in as much as a 30 percent increase in lighting energy efficiency. According to the Washington, D.C.-based Energy Information Administration, electronic ballasts have saved an estimated $15 billion in commercial buildings’ energy use since 2005.
Another focus area is increased attention to lighting-design techniques. From daylighting to lightshelves to task lighting, designers are employing multiple strategies to reduce the overall number of fixtures needed to achieve the same lighting levels. For the fixtures that remain, highly efficient fluorescents and LEDs are being carefully considered. Fluorescent Lamps
Fluorescent lamps are significantly more energy efficient than incandescent bulbs because they require less energy to provide the same amount of light. CFLs can use up to 75 percent less energy than incandescent lamps and last up to 10 times longer, which is roughly 5,000 to 10,000 hours more depending on the specific CFL. These statistics represent performance under ideal conditions and do not apply to all applications. For instance, CFLs are not well suited for enclosed light fixtures, like ceiling can lights, because of the decreased airflow and subsequent build-up of temperatures. Although CFLs do not produce as much heat as incandescent bulbs, some components cannot withstand the heat, causing the light output to be reduced or the product to fail. This can be avoided by choosing CFLs specially designed for such applications.
CFLs contain 5 mg of mercury in the form of vapor with larger fluorescent bulbs containing slightly more mercury. This is about 1/100 of the amount of mercury found in a mercury fever thermometer. When the electric current is switched on, the mercury vapor is energized, causing it to send out UV energy. Without the mercury vapor to produce UV energy, there would be no light.
The phosphor coating on the CFL’s glass tube absorbs the UV energy, which causes the phosphor to fluoresce and send out visible light. Combining different phosphors determines the color temperature of the light emitted by the bulb.
The mercury content of CFLs is a concern for some potential users. In reality, use of CFLs actually prevents mercury releases into the environment because of the lamps’ increased efficiency. Electricity use is the main source of mercury emissions in the U.S., according to the U.S. Environmental Protection Agency, Washington. During a light source’s estimated five-year life, a power plant emits 10 mg of mercury to produce the electricity to run an incandescent lamp compared to only 2.4 mg of mercury to run a CFL. The EPA, however, is working with CFL manufacturers and retailers to expand recycling programs nationwide. (For information about what to do if a CFL breaks, see “When the CFL Breaks,” page 58.)
Light-emitting Diodes LEDs have been available in the U.S. since the 1960s and have been used primarily for indication purposes, such as in signs, signals and electronic equipment. Today, LEDs are starting to compete with conventional-light sources in general-illumination applications, such as for rooms or task lighting over desks.
LEDs are classified as solid-state lighting because the light is emitted from a solid object—a block of semiconductor—rather than from a vacuum or gas tube, like an incandescent or fluorescent. According to the Washington-based U.S. Department of Energy, solid-state lighting has the potential to revolutionize the lighting market through the introduction of highly energy-efficient, longer-lasting and more versatile light sources. Early marketing claims boasted that LEDs lasted for 50,000 to 100,000 hours, which was vastly overstated. According to the Lighting Research Center at the Troy, N.Y.-based Rensselaer Polytechnic Institute, newer, improved LEDs have the potential to provide good light output for as many as 25,000 hours. LED useful life typically is based on the number of operating hours until the LED is emitting 70 percent of its initial light output.
Unlike incandescent or fluorescent lamps, LEDs generate little or no infrared or UV light. However, they convert only 15 to 25 percent of the power they consume into visible light; the remainder is converted to heat. Thermal management in LED-lighting products is a critical issue. Excess heat directly affects short- and long-term LED performance. The short-term effects are color shift and reduced light output; when the lamp cools these effects disappear. Long-term effects are accelerated lumen depreciation and shortened useful life. To solve these problems, manufacturers include a heat sink in direct contact with the LED junction to conduct heat away from the light source.
Many lighting manufacturers are racing to develop cost-competitive, high-quality LED products for general-illumination purposes. This is understandable, given that LEDs typically use 80 percent less energy than incandescents and 30 percent less energy than CFLs. LEDs also can be dimmed more cost effectively by varying the current and do not have the mercury issues that plague fluorescent lamps. Several important factors currently are holding LEDs back from mass production and appeal. The first is production costs caused from a variety of expensive components, like heat-sink materials (aluminum), AC/DC converters, etc. The second factor is that LEDs are a heat source and can damage other components in the fixtures if the heat is not properly dissipated. Color consistency also has been a problem for some LED manufacturers, though this is changing as the science behind LED-semiconductor manufacturing matures.
An important step to creating customer confidence occurred in late 2008 with the creation of Energy Star criteria for LED fixtures. Qualified LED commercial products must use at least 75 percent less energy and last 35 times longer than incandescent lighting. Other validation mechanisms, such as third-party testing from organizations like the Davis, Calif.-based California Technology Lighting Center, help provide much-needed credibility.
Making Informed Choices Early adopters of CFLs and LEDs may have fallen prey to the exaggerated marketing claims of some overzealous manufacturers. Despite alienating some potential users, these lighting technologies deliver impressive energy savings with marginal environmental risk. To succeed, specifiers must choose products designed to accommodate the unique characteristics of a particular application. Seeking market leaders with independent product testing can further help substantiate performance and environmental claims. Armed with this knowledge, green-building practitioners will deliver a proper lighting fit.
Scott Florida writes about architecture and sustainability from Oakland, Calif.