sparrowpost

As the holiday decorations go up this year, I’ve noticed more and more homes using LED Christmas lights rather than the old incandescent standbys. I can easily pick the LED out because the light color generally hovers closer to the blue/ green end of the spectrum than the red/yellow old-fashioned lights. Seeing LED move into consumer lighting applications is really exciting.

LED stands for Light Emitting Diode. While old fashioned Christmas lights use the same technology as old fashioned light bulbs (heating a very thin wire until it glows by running electrical current through it) and tend to produce more heat than light, LEDs use a semi-conductor that, when energized, encourages electrons to jump across a polarized differential. The change in energy state of the electrons as they fall from one side to the other creates light. There is a lot more on the basics of how LED works at http://electronics.howstuffworks.com/led.htm and wikipedia.
Suffice to say that LEDs create light with very little heat, and because no energy is wasted heating things, LEDs are often more than 90% more efficient than incandescent lights!

While LEDs have been in the consumer market in a variety of technologies for a long time (digital readouts on your oven, your watch, etc), they have only recently begun to be used in lighting. There are great expectations amongst scientists and energy-efficiency wonks that LED will soon replace fluorescents as the longest lasting, most energy efficient lighting source in a range of applications. You can already see LED lights in action lighting stairs and walkways, in battery operated bicycle lights, and in the picture above of my car with an LED stick-on light (LED Christmas Lights just visible through the windows of the vehicle). Because they are very long lasting, they are great in locations that are difficult or troublesome to regularly service, such as streetlights and traffic signals. Many cities have already changed all their traffic signals to LED, not only reducing maintenance cost, but also reducing the greenhouse gas emissions from the city through significant energy savings.

There will be a couple stumbling blocks to overcome before LED lights are widely used for consumer lighting. First, LEDs are quite expensive, and become more expensive as LEDs become brighter. Brighter LEDs require better semi-conductors, and while the price for these is coming down, they can still be quite expensive. A low-end LED replacement for a small halogen light can easily cost $20 wholesale.

Another difficulty stems from the fact that LEDs always produce non-white light. The color of LEDs is determined by the band gap of the metal used as a semiconductor. While semiconductors with a band gap that produced green and red wavelengths are relatively easy to come by, it took a bit more effort to come up with semiconductors that would make yellow and blue light. The light sources we traditionally use in our home are yellow/ white, and high brightness LEDs in these colors have not yet been produced. In order to make the “white” LED demanded by the market, most manufacturers simply put a yellow filter of some variety (coating, plastic lens) over a blue LED. While the light color that results is more familiar to eyes accustomed to tungsten lights, the filtration process cuts the lumens (strength) of the light produced, making super-bring LED that much more important.

When you look at the LED-decorated Christmas tree at the top of this post, you’ll notice that the blueish hued lights stand out much more than those that have been filtered or produced in other colors. While the differences in light color might take a little getting used to, the energy saving possibilities for LED, combined with their long life and the absence of toxic mercury in their composition make them one of the super-technologies that we will look to for help in the coming decades.

You can get started now with LED desk lamps http://store.sylvania.com/show_item.cfm?i=72111 . and LED Light Bulbs. Please post below about your experiences if you have used/ are using LED lights in your home.