Consumers Warm to Energy-Saving Bulbs, but Quality of Light Is a Hot-Button Issue
Long-lasting compact fluorescent light bulbs use far less energy than traditional incandescent light bulbs.
(By Blaine Harden -- The Washington Post)
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Every green-building expert says the easiest way to make your house more environmentally sensitive is to change all the light bulbs, replacing your incandescent ones with compact fluorescent light bulbs. They produce the same amount of light with about 75 percent less energy.
For the average household, this would reduce total energy consumption by 9 percent, a big deal. An added plus is that compact fluorescents last eight to 10 times as long. It sounds like a no-brainer.
But the experts don't mention the color of the light that compact fluorescents give off. It can look horrible, as I discovered after I installed several in ceiling fixtures.
Described on the packaging as "daylight," the color wasn't bad at dusk. At night, it looked ghastly, though, missing by a mile the standard by which, I belatedly realized, we judge all interior illumination -- light from an incandescent bulb.
The irony here is that incandescent light is itself artificial -- it's warmer and redder than sunlight.
Knowing that my "daylight" compact fluorescents were one of many choices available, I set out to find an aesthetically acceptable alternative.
There are two critical distinctions that affect our perception of light: the color-rendering index and the Kelvin temperature scale.
The color-rendering index indicates how the colors of objects under a given compact fluorescent appear to human eyes. Color is clearest and truest with sunlight, which has an index of 100. Incandescent bulbs have an index that is nearly as good, which is why most people prefer them.
Most compact fluorescents have a color-rendering index in the low to mid-80s. Lighting engineers may characterize this as "excellent," but most people notice that something about the light is different.
The Kelvin designation is commonly used among lighting engineers but foreign to nearly everyone else. Kelvin temperature is the amount of heat required to produce a particular color of light as a black body is heated from a cold black to a white-hot state. It's a precise way of identifying the colors in the electromagnetic spectrum that are visible to the human eye. At lower Kelvin temperatures, the color of the light is red; at higher temperatures, it's bluish.
This distinction confuses most people because they characterize color in psychological terms, not scientific ones. Red is warm and loving; blue is cold and harsh. Here's a tip to help you keep it straight: If you recall your astronomy lessons, red stars are older and cooler, while blue stars are younger and hotter.
Why do you need to know about Kelvin temperatures? Because for a given wattage, most manufacturers offer bulbs with different Kelvin temperatures, each with a distinctly colored light. If you don't know anything about Kelvin temperature, you won't know what you are buying beyond the general descriptive terms such as "soft white" that are on some packaging.
