Solid-State Lighting that Uses 50 Percent of the

Power Consumption of Conventional Lighting

At present, electricity use accounts for about one-third of total energy consumption in the United States.

Of that, about 20% of all electricity consumed goes for lighting. However, today’s lighting is remarkably inefficient. Incandescent lights have a luminous efficiency of 15 lumens/watt and fluorescents a luminous efficiency of 80 lumens/watt. This corresponds to only about 5% and 25% respectively of the electrical energy being converted to visible light. By comparison, building heating is typically 70% efficient, and electrical motors typically 85-95% efficient, depending on their size. Lighting therefore represents a large target for improved energy efficiency. Cutting the amount of electricity needed for lighting in half would result in a savings of 4 x1011 kilowatt-hours of energy per year – roughly equivalent to the annual energy production of 50 nuclear reactors.

The use of semiconductor-based light emitting diodes (LEDs) for general illumination is a rapidly developing technology that offers the potential of immense energy savings to the nation and the world within a decade or two. For colored lighting, LED’s have already replaced over one third of the traffic lights in the United States, resulting in a savings of about $1000 per intersection per year. However, a number of science and technology obstacles must be overcome in order for solid-state lighting to reach

its potential. The research target now is to bring this new technology to the general white lighting applications where the potential impacts are tremendous. This will require producing white light. To do

Efficiencies of Energy Technologies
in Buildings:
Heating:	70-80%
Electric motors:	85-95%
Fluorescent lighting:	25%
Incandescent lighting:	5%

so, one can have a source consisting of three or more different colored LEDs, or use ultraviolet light to illuminate phosphors that emit the different colors. The latter approach is by far the most economical and much higher efficiencies have been demonstrated using semiconductor nanocrystals (quantum dots) as phosphors. Before these devices can be made commercially available, improvement is required in the ability to incorporate quantum dots into the dome above the illuminating LED in a manner that retains their high efficiency.

World’s first white light LED-based light source using only quantum dots as phosphors. The LED chip is a 410 nm InGaN-based chip from Cree Research (J. Simmons, Sandia National Laboratories).