NOTES ON LED LIGHTS

Light emitting diodes (LEDs) are solid-state lighting components. They have no moving, fragile parts and can last for decades. LEDs can be many times more energy efficient than light bulbs, depending on the application. Just as vacuum tubes in televisions were replaced with solid-state components, the last remaining vacuum tube light bulbs are being replaced by solid-state components.

Imagine a grain of sand that emits a very bright light, usually red, amber, green or blue, depending on the material, when an electrical current is applied. That's essentially an LED. The actual science and manufacturing process to develop an LED is quite complex, but the principle is simple.

The first LEDs for commercial applications were red. They functioned as on/off or indicator lights in electronic devices such as VCRs, calculators, stereo systems and even automobile subsystems. Eventually, LEDs were produced in green and amber as well. The major breakthrough came in 1989 when Cree, Inc. of Durham, NC, started shipping the first commercially viable blue LED, based on silicon carbide. That blue LED enabled white LED-based light. Mixing red, blue and green light produces white light.

Today, a more-efficient and cost-effective white LED light is revolutionizing the lighting world. The white power LED, based on a blue LED chip coated with a phosphor, is bright and efficient enough to be used in general illumination. Fixture manufacturers are making LED-based products for outdoor street, walkway, parking and indoor-down light applications.

Cree introduced the first lighting-class white power LED in 2006 and followed up with the first lighting-class warm (softer) white power LED in early 2007. LEDs are ready for general-illumination applications, presenting a dramatically enhanced lighting option to save energy and maintenance costs as well eliminate the hazardous-waste issues associated with mercury-containing light bulbs and tubes.

History of Light (& Heat)

The history of man-made light is based on heat. Wax, oil and gas burn to produce light. The filament in an incandescent bulb heats up to produce light. Gas in a fluorescent tube is zapped to illuminate. The basic method is "Heat it up, and it glows."

For more than 120 years, incandescent light bulbs have brightened and literally warmed our lives. Electric-powered bulbs were a major improvement over candle, gas and oil light sources, but they are extremely inefficient. Bulb-based light sources are far better at producing heat than light - up to 90 percent of the power going into a bulb is converted to heat.

Compact fluorescent bulbs (CFLs) are more efficient, and are an excellent alternative to incandescent bulbs for Edison-socket light fixtures. However, they contain a small amount of mercury, making them hazardous waste when they break or burn out.

In the past 12 months, a new light source has emerged that is sufficiently bright and efficient to be used for general illumination. The light emitting diode, commonly called the LED, uses far less energy and can last many times longer than most bulbs and contains no lead or mercury. Cree, Inc. introduced the first commercially available lighting-class LED in late 2006. Lighting manufacturers are now producing a whole new class of LED lighting products for general illumination.

LEDs are now ready for broad deployment across general lighting applications such as parking garages and lots, streetlights and other outdoor installations. Indoor directional and down light solutions are also becoming available. According to the University of California, Santa Barbara, widespread deployment of LED-based lighting could save $280B in electricity costs in the U.S. alone by 2025.

By committing to LEDs in municipal lighting, cities are making a thoughtful energy choice that will greatly benefit their taxpayers, visitors and the environment.