Recent Trends in Solid State (LED) Lighting

The acceptance of Light Emitting Diodes (LEDs) as the preferred lighting device continues to grow in all sectors throughout our country, but especially in municipalities. U.S. cities are seizing upon LEDS as a viable strategy to “Go Green”, particularly in applications where low maintenance is more important than lower initial costs.

According to an article entitled “U.S. Cities Go Green with LEDs”, in the Optical Society of America’s (OSA) February issue of Optics and Photonics News (OPN), cities as well as public and commercial institutions are demonstrating the use of LEDs to realize long term cost savings and reduce pollution in the operation of traffic lights and street lighting. Although LED’s are still more expensive than fluorescent lights, their initial costs are offset by their higher efficiencies and longer lifetimes. Maintenance costs to replace failed lighting are very expensive in street lighting and traffic lights. And LED’s don’t usually “fail suddenly”, like incandescent and fluorescents. When they begin to fail their light production usually drops about one-third, which means that there is more time to schedule and coordinate repairs.

James Brodrick, manager of the DOE’s solid state lighting program, claims that the use of high efficiency LEDs could reduce U.S. energy consumption for lighting by over 30% in two decades, which would eliminate the need for 44 power plants generating 1000 megawatts each, and cut the equivalent of 47 million automobiles’ greenhouse emission. LEDs are also more efficient in outdoor lighting because they are more directional and can be applied where they are needed. The clean, uniform lighting provided by LEDs also improves visibility.

All new traffic signals now use LEDs, which provide a cost savings of approximately $48/year, due to reduced maintenance and the fact that LEDs produce the desired colors, rather than having a broad band source that has to be filtered, like fluorescents and incandescents.

The DOE is encouraging the use of LEDs by funding municipalities and educational institutions for demonstration and test sites. (Visit http://www.ssl.energy.gov/ for more information.) The OPN article, cited above, describes several successful examples of DOE-funded initiatives.

LED use is also growing in home use, particularly in outdoor lighting. But the cost and reluctance to switch to a somewhat different lighting effect have delayed widespread use like municipalities have experienced. “The Energy Independence and Security Act of 2007, which set efficiency standards for light bulbs, is also helping to promote LED use. Traditional incandescent bulbs do not meet the standards that go into effect in 2012”, Brodrick said. “By 2020, advanced incandescents will fall below the standards as well. Only CFLs and LEDs are likely to meet the 2020 standards.

OP-TEC continues to follow LED technology advances in lighting, in order to anticipate the need for new technicians in this field. So far most of the production and installation jobs appear to be at

the craft level.

Questions or comments? Please contact us!

Click here to read the full OPN article, "U.S. Cities Go Green with LEDs."

Click here to visit the DOE's Solid State Lighting website.

Solid State Lighting: Energy Conservation through Improved Photonic Efficiencies

Energy resources and energy consumption aren’t just hot topics for the news media: they’re major, world-wide issues that we must confront for the next few decades. Last week I talked about recent developments in solar electric (voltaics) that may lead to its widespread growth as a renewable energy source. This week, I want to look at how photonics will contribute to energy conservation.

Lighting consumes over 20% of all the electrical energy produced in the world. The incandescent bulb is only about 25% efficient. We are not only losing 75% of the energy supplied to incandescent, in many cases this wasted energy is producing unwanted heat that will require more energy to remove it. Several states and other countries have already moved to ban the sale of incandescent bulbs this year and through 2012. It’s likely that this ban will grow to most or all states soon.

Presently, compact fluorescent lamps (CFL) and fluorescent tubes are the choice for room lighting in most commercial and residential buildings. But fluorescent lighting is only 40% efficient, its color tone does not match sunlight (an aesthetic quality we hold dear) and when they are no longer useable, we have to dispose of devices that contain mercury, which is harmful to the environment.

Solid state lighting (light-emitting diodes, or LEDs) shows the greatest promise for improved lighting efficiency and energy conservation. LED’s have the potential of being over 90% efficient and lasting for 50,000 hours (as compared with a few thousand hours with incandescents and CFLs.) Typical LEDs emit a single color of light from a small source (semiconductor junction.) If we want to use them as white light sources, we have to combine at least three LEDs with different emitting color characteristics. (i.e., red, blue and green) Some optical elements are usually placed in front of the LED’s to spread or diffuse the “point source”.

Presently, LEDs are in use in the following niche applications:

• Colored Light Sources—Traffic lights, exit signs, candles and holiday lighting
• Indoor White Light—Recessed down lights and refrigerated display cases
• Outdoor White Lights— Street and area lights & step, path and porch lights

Of these, the greatest energy savings are coming from recessed down lights and street/area lights (luminaries). For room and hall lighting in commercial and home buildings, special power supplies are being developed to control dimming and color temperatures. These power supplies are the limiting factor on lifetime (~6-10,000 hours).

In May, 2008, General Electric announced the demonstration of roll-to-roll manufactured organic light-emitting diode (OLED) lighting devices. This product will be available in thin sheets which, presumably, could be applied to walls or ceilings of rooms. The OLED offers the potential of having entire walls or the ceiling emit light at controlled colors and levels of intensity.

So, what new or renewed jobs will solid state lighting produce as it inevitably will emerge in the next several years? Will it require retraining for electricians, architects and room designers? Or, will there also be a need for SSL technicians with comprehensive knowledge and skills to rebuild our lighting infrastructure for more energy-efficient consumption?

OP-TEC staff will continue to follow this emerging application of photonics to anticipate new education and training needs.

To learn more about solid state lighting visit www.netl.doe.gov/ssl.