Light Emitting Diodes (LED) have historically been most commonly used as state indicators, for example, as a "Power On" indicator. The light output from the LED was low, but the advantages for the designer were that the LED energy efficiency was terrific, was capable of "instant on" operation, and that the reliability and lifetime were very good. Another advantage is that an LED contains no hazardous materials like mercury.
outlook for LED use is improving. There
has been much advancement in LED technology in the last few years, allowing new
applications. The manufacturing cost of
LEDs has been relatively expensive because the process used a sapphire substrate.
reason for the changing outlook is the need for energy efficiency. A law passed in 2007 requires all light bulbs
to become more energy efficient. Over a three-year period, starting in 2012,
new bulbs will have to use 25 percent less energy, for the same light output,
as incandescent bulbs. Currently, the only light technology in widespread use
that meets that standard are compact fluorescents,
which use 70 percent less energy.
Today, compact fluorescents account for less than 20% of total bulb
sales. With a more efficient light source, the energy is saved in two
areas. The lamp uses less electricity,
and less energy has to be spent cooling the
An interesting example of a new LED application is cities replacing their incandescent traffic lights with LED arrays. This is happening because the electricity costs can be reduced by 80%, and the maintenance costs are also reduced. Let’s assume that a traffic light uses 100 watt bulbs. The light is on 24 hours a day, so it uses about 2.4 kilowatt-hours per day. If we assume power costs 8 cents per kilowatt-hour, it means that one traffic signal costs about 20 cents a day to operate, or about $75 per year. If we assume eight signals per intersection, that's about $600 per year in power per intersection. An LED array should consume less than 20 watts (instead of 100), so the power consumption drops by a factor of 5, to less than $120 per intersection. For a city with many intersections, that can add up.
application is the use as a light source in High Definition Televisions (
fluorescent lighting in a
LED is a new, old technology that is changing our world for the better.