** Spotlights **

Traffic signals, pedestrian signals, and exit signs consume significant amounts of energy. U.S. buildings have more than 100 million exit signs, which cost $1 billion annually to operate. An estimated 3 to 4.5 million traffic signals are operating on the nation’s streets at a cost of approximately $2 billion annually. Municipalities can reduce energy costs, air pollution, and greenhouse gas emissions by replacing conventional incandescent fixtures with light-emitting diode (LED) traffic and pedestrian signals and exit signs.

LEDs are semiconductor chips that convert electrical energy directly into light. They do not have “bulbs” like conventional lighting technologies, but they do use a lens to concentrate and direct the light. LEDs use much less power and last much longer than incandescent lights. They are efficient, give off little heat, and can be embedded in plastic and other durable materials.

Early versions of LED technology had very low light output and were used primarily for indicator lights on electronic equipment. During the 1990s, however, industry developed brighter LEDs that are suitable for use in traffic and railroad signals, exit signs, and automobile turn and brake signals. For such applications, LEDs are bundled together to provide adequate illumination.

Replacing a red incandescent traffic signal head with a red LED unit will cut energy use by an estimated 82 to 93 percent. The payback for the initial investment in red LED traffic lights is approximately 2.5 to 3 years through energy savings. The actual payback period depends on energy prices, the cost of the units, and any financial incentives offered by utilities or government agencies.

LED traffic signals are estimated to last 5-10 years before they must be replaced, compared with 1 to 2 years for incandescents. Maintenance costs thus are expected to be lower with LEDs. The longer life and greater reliability of LEDs also may help reduce the risk of lawsuits against municipalities for accidents caused by burned-out traffic signals.

Red traffic signals and pedestrian “Don’t Walk” signals are the most cost-effective candidates for replacement with LEDs. Red LEDs cost less to manufacture than green or amber LEDs and they are more luminous, requiring fewer individual LEDs per signal. However, electricity rate structures in some locations may make green LED traffic signals cost-effective, and a number of states and cities have begun to install them at intersections. Green LEDs also may be used for pedestrians’ crossing signals.

LEDs also work well for exit signs: LEDs are more efficient and more visible in emergency egress situations than standard incandescent signs. A standard 40-watt incandescent exit sign can be replaced with a 5-watt LED sign. A 1999 survey by the Lighting Research Center at Rensselaer Polytechnic Institute found that about 80 percent of the exit signs sold in the United States in 1998 used LEDs as the primary light source. Retrofit kits for converting existing exit signs to LEDs are now available on the market, and installation may take as little as 15 minutes.

Blue, amber, and phosphor-coated “white” LEDs are becoming available and may be used increasingly in the future for a wide range of signal and sign applications, including roadway sign lighting. LEDs also are being used for directional path markers along pavements and walkways. LED “light bulbs” (screw-mounted lamps in the shape of incandescent bulbs) are available for beacon and accent lighting, and for a wide variety of retail lighting applications.

The economic and environmental savings of LED traffic signals can be substantial. In Colorado, the City and County of Denver began upgrading traffic signals to LEDs in 1996. All of the area’s 17,036 red traffic signals and “Don’t Walk” signals have been converted. Energy costs have dropped by approximately $20,000 per month, and the city estimates annual savings of $128,000 in material and labor costs. The net savings over the lifetime of the LED units is expected to exceed $5.1 million. The project will avoid an estimated 8,894 tons of greenhouse gas emissions annually, as well as 6.4 tons of sulfur dioxide and 6.7 tons of nitrogen oxides. Denver is preparing to convert all of its green traffic signals to LEDs and anticipates savings comparable to those from installing the red units.

Potential barriers to LED traffic signals include their initial cost, lack of information about LEDs, and uncertainty about performance and reliability. LEDs also are temperaturesensitive, and special measures must be taken for installation in high-temperature climates.