LED street light

LED street light

The LED street light (also referred to as LED road lighting) is an integrated light-emitting diode (LED) light fixture that is used for street lighting. LED street lights can reduce the cost of keeping streets well-lit when dark.

Design and style

LED street light beam pattern

An LED street light is an integrated light that uses LEDs as its light source. These are considered integrated lights because, in most cases, the luminaire and the fixture are not separate parts (except LEDGine-based luminaires). New in manufacturing, the LED light cluster is sealed on a panel and then assembled to the LED panel with a heat sink to become an integrated lighting fixture.

Different designs have been created that incorporate various types of LEDs into a light fixture. The current trend is to use high power 1 watt LEDs, but some companies use low power LEDs in their products, including several low power LEDs packed together to perform the same purpose as a single high power LED. The shape of the LED street light depends on several factors, including LED configuration, the heat sink used with the LEDs, and aesthetic design preference.

Heat sinks for LED street lights are similar in design to heat sinks used to cool other electronics such as computers. Heat sinks tend to have as many grooves as possible to facilitate the flow of hot air away from the LEDs. The area of heat exchange will directly affect the lifespan of the LED street light.

The lifespan of an LED street light is determined by its light output compared to its original design specification. Once its brightness decreases by 70 percent, an LED street light is considered to be at the end of its life.

Most LED street lights have a lens on the LED panel, which is designed to cast its light in a rectangular pattern, an advantage compared to traditional street lights, which typically have a reflector on the back side of a high-pressure sodium lamp. In this case much of the luminance of the light is lost and produces light pollution in the air and surrounding environment. Such street lights can also cause glare for drivers and pedestrians.

A drawback of LED focus panels is that most light is directed to the road, and less light to the footpaths and other areas. This can be addressed by the use of specialised lens design and adjustable mounting spigots.

Energy efficiency

The life span of an LED as compared to other light sources^{[citation needed]}

The primary appeal of LED street lighting is energy efficiency compared to incandescent bulbs of the same luminance. Research continues to improve the efficiency of newer models. One such advance can be found in a street light product created by Lighting Science Group Corporation. One model of LED street lights produced by this group is up to 60 percent more efficient than previous models, lasts for 12 years, and allows for cost recovery through energy savings in only three years.

An LED street light based on a 901 milliwatt output LED can normally produce the same amount of (or higher) luminance as a traditional light, but requires only half of the power consumption.

As the LED lighting fixtures normally produce less lumen/Watt illumination it is very crucial to have a well distributed illumination pattern in order to do the same job as higher lumen/Watt conventional fixtures. So a good design of LED street lights is to point different LEDs in one fixture to different target points.

Advantages

• Low power consumption and long and predictable lifetime

The lifetime of LED street lights is usually 10 to 15 years, three times the life of current technologies adopted. LEDs also have low maintenance cost.

• Dimming

LEDs can be dimmed when less street lighting is needed, such as late nights and early mornings.

• Small package size
• More accurate color rendering

The color rendering index is the ability of a light source to correctly reproduce the colors of the objects in comparison to an ideal light source.

• Quick turn on and off

Unlike fluorescent bulbs, which take time to heat up once switched on, LEDs turn on instantly, and do not have a problem restarting immediately after being turned off (hot ignition).

• RoHS compliance

LEDs don't contain Hg/Pb and don't emit poisonous gases.

• Less attractive to nocturnal insects

Insects are sensitive to the UV-blue and green region of the light spectrum. Nocturnal insects are attracted to the emission of UV-blue and green light from conventional light sources. White LEDs, however, emit light in a small peak in the blue range and smaller in the green range, so nocturnal insects are less attracted to such light sources.

• Easy to design non-glare lighting equipment

Most LED street lights have a lens on the LED panel, which is designed to cast its light in a rectangular pattern, an advantage compared to traditional street lights, which typically have a reflector on the back side of a high-pressure sodium lamp. In this case much of the luminance of the light is lost and produces light pollution in the air and surrounding environment. Such street lights can also cause glare for drivers and pedestrians.

• Higher light output even at low temperatures

Notable installations

LED street lights have been installed or announced for installation in several large cities as well as smaller cities throughout the world. The United States Department of Energy has available a number of reports on the results of many pilot projects for municipal outdoor lighting. Cities that have announced their intention to install LED street lights include Boston, Worcester, and Cleveland.

Cities that have installed at least some LED street lights include:

• Los Angeles, California
• Ames, Iowa
• Arlington, Massachusetts
• Des Moines, Iowa
• Woodland, California
• Varna, Bulgaria, A2 Highway
• Toronto
• Dallas, Texas
• Richmond, BC
• Reno, Nevada
• Budapest
• Vilnius, Lithuania
• New York City
• Washington, D.C.
• Baltimore, Maryland
• Springfield, Massachusetts
• Mesa, Arizona
• Adelaide, South Australia
• Miri, Subang Jaya, Pontian, Kuala Lumpur - Karak Expressway, Federal Highway in Malaysia
• Hanscom Air Force Base, Massachusetts
• Cebu City, Philippines
• Bristol, United Kingdom
• St. John's, Newfoundland and Labrador
• Halifax, Amherst, Annapolis Royal, Wolfville, Halifax International Airport, Truro, Antigonish, and many other smaller towns in Nova Scotia have installed fixtures manufactured and designed by a company in that province.
• Seattle, Washington
• Warren, Michigan

External links

• U.S. Department of Energy reports on municipal LED lighting pilot projects: Solid-State Lighting GATEWAY Demonstration Results
• New Streetlights – LED streetlight news and analysis