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.