Here’s a quick experiment: with all the regular lights turned off for the evening, walk through your darkened home to count what’s still glowing. Your list might include the red numbers on a coffeemaker or clock radio, green numbers on the stove, microwave, or VCR, and red dots on a smoke detector or DVD player.
Light-emitting diodes (LEDs for short), the technology that makes these little lights possible, have become so common we rarely think about them.
But LEDs are offering innovative choices that also conserve energy.
LED light is quite energy efficient, with very little heat as a wasted byproduct. LED lights have an extremely long life, requiring little maintenance. And their small size allows them to fit in confined spaces.
These advantages are possible because LEDs operate in an entirely different way than traditional bulb lights.
An incandescent light uses electricity to make a filament glow, while a fluorescent uses electricity to make gases glow. But light-emitting diodes are actually semi-conductors, which are electronic gateways that form the basis for devices like transistors and computer microchips. LEDs are a special kind of semi-conductor that emits visible light when an electric current passes through it. No filaments or gases are needed. Glass is not a necessary part of an LED either: an LED can operate safely with just a thin sheet of plastic over it.
But until recently, three main disadvantages of LEDs prevented their widespread use.
First, colors are limited since the chemistry of the diode determines the color of the light. In the early days, you could get any color LED you wanted—as long as it was red. Then inventors figured out a way to build LEDs that emit green light. Yellow and blue followed, with near-white light LEDs just entering commercial production in the last two years.
Second, the light from LEDs isn’t very bright. The numerals on an LED display seem bright enough on an appliance, but that’s because it’s contrasted against a dark background. LEDs gleam, but generally don’t produce enough lumens (the unit of brightness) to actually shed light into the surrounding area. It’s also difficult to direct the light from an LED. This means it’s best to look straight at LEDs, not use them to create pools of light on surfaces.
The third limiting factor has been cost. The few LEDs needed to create small digital displays are economical to produce, but larger configurations have remained limited by high manufacturing costs. Although the cost per amount of light output has steadily declined during the last 15 years, larger arrays of LEDs still require a substantially higher initial investment.
Yet today’s newest LEDs are filling important niches in lighting. LEDs are an excellent choice for special effects such as the gigantic advertising signs in New York’s Times Square and flat screens at sporting arenas.
LEDs also offer a viable alternative to neon. Tetra Channel Lighting Systems, a trademarked product offered by the GELcore Company, was introduced in 2002 as a substitute for neon. Encased in plastic, it can be easily formed into a variety of shapes to outline building edges, create artistic decorations, and spell words.
This past summer GELcore introduced a new form of street lighting. Instead of a sign lit by a bulb shining on it, the sign has an LED inside. It provides light with no ballasts or bulbs to change, so although the initial cost is high, it’s very inexpensive to operate. Similar signs are now taking the place of traditional traffic signals and lane markers.
Indoors, LED arrays are now available for such specialty situations as outlining service areas, exit signs, and emergency lighting.
Next month: Accessing the Internet over power lines