LEDs and Home Lighting Technology

Abstract

ONE OF the best parts about writing this column is that I have to learn something before I can write about it. That's the fun part. This time, I had to learn about home illumination. Specifically, I wanted to see if LED (light-emitting diode) technology was a feasible option for home lighting. Most of the sources I consulted predicted that LED home lighting was 10 years in the future. Because I think technology moves faster than this, I'm predicting three years. Obviously, I will report my findings, but first I think a primer on light, color, and the various technologies used to illuminate our homes is in order. There are numerous technologies used in home lighting, including tungsten incandescent, quartz halogen, fluorescent, and LED. Low-pressure sodium is more common in such outdoor applications as street lighting. These various technologies have distinctive advantages and disadvantages. The most familiar have been around for more than 100 years, and they are inexpensive. But a major disadvantage is that they are inefficient and waste a lot of energy in the form of heat. In addition, incandescent bulbs have a short lifetime. Incidentally, the regular screw-in base is called the Edison base, which can be useful to know for online searching. Fluorescent lighting is a great deal more efficient than incandescent lighting, but the tubes are fragile, require ballasts that sometimes hum, and contain mercury. Newer compact fluorescents eliminate many of the disadvantages of the large fluorescent tubes. Halogens are more efficient than incandescents but share many of their disadvantages. The newest kid on the block, LEDs are 10-20 times more efficient than incandescents, so they use substantially less electricity. LEDs are also rugged and have a lifetime of more than 100,000 hours. Because I get tired of changing light bulbs, this is a very attractive feature. LEDs are small, so they must be combined into arrays or clusters. And because LEDs are low-voltage devices, using them in home lighting requires a power supply. In an LED light bulb, this power supply is built into the base of the bulb. White LEDs have generally not been available, but manufacturers are working feverishly to change that. We have all grown used to buying light bulbs with various wattage ratings, such as a 40-watt or 60-watt bulb. Light output, however, is measured not in watts but in lumens. Don't ask for a simple definition of a lumen, because it gets complicated. But a standard 40-watt bulb produces about 390 lumens, while a 75-watt bulb produces about 1,055 lumens. (The figures are for Sylvania Double Life Soft White bulbs.) The efficiency of a light source is measured in lumens per watt. According to references in Wikipedia, the lighting technologies mentioned above have the following efficiency ratings in lumens/watt: 40-watt tungsten, 12.6; quartz halogen, 24; fluorescent, 56; LED, 131; and low-pressure sodium, 200. All light is not the same color. The sun at noon is nearly perfect light because all the colors of the spectrum are evenly present. Home lighting merely approximates There are several descriptors that manufacturers of home lighting use to describe the color of the light produced. The four most common are soft white, cool white, warm white, and sunlight. I believe that soft white means that the light is evenly dispersed from the bulb. …