We’ve heard a lot lately about how LEDs or ‘light-emitting diodes‘ are set to revolutionize the world of lighting. Traditional sources of lighting, such as incandescent and halogen bulbs, are inefficient. Fluorescent bulbs bring dangerous mercury into the home. White LEDs promise to change this, bringing cool, efficient, mercury-free lighting.
And if you haven’t heard about it lately, White LED technology revolution is flaring up rapidly and this could very well be the first radical change since Thomas Edison!
When White Isn’t White
Unfortunately, nothing is quite that simple. Newer LEDs provide a new problem of their own: coloration. To understand this problem, it is important to understand how white LEDs work. Most white LEDs are actually blue LEDs. A phosphor is then added to the outside, which changes the color of the emitted light from blue to white.
Problems With Phosphors
The problem is fairly straightforward. The quality of these phosphors is wildly different, and LEDs are effectively made by trial-and-error. Depending on the cost of the LED, you can expect up to fifty diodes to be made for every one useable white diode. Aside from the obvious environmental consequences of this, it creates some substantial issues with coloration.
In effect, you’ll get what you pay for. The more diodes a company is willing to dispose of, the whiter your diodes will be. There currently aren’t any clear standards for calling a diode “white”, so it is important to be a wary consumer.
There are two ways around this problem. The first is to be find out the standard your company uses for sorting its LEDs. The wider the range of color temperatures your company uses for sorting, the less even your lighting will be. You should look for a range within about 200 degrees Kelvin. For environmental reasons, you may also want to check what happens to the unused LEDs, and whether they are discarded (bad) or find their way into lower-cost items like flashlights (good).
The second solution is to simply not use blue LEDs at all, and instead switch to the newer RGB LEDs. These create the illusion of white light by mixing three colors together, and is not dependent on mixed-quality phosphors. On the downside, RGB LEDs are more expesnsive than phosphorous ones.
Guest Author: This is a guest article by Daniel Bader, Ph.D., who is the webmaster and lead writer for the website Home Lighting Design, a site that helps non-specialists learn the basics of lighting design. He lives in Toronto with his wife and two children.