Why is incandescent lighting better in residential construction than metal halide, high-pressure sodium, or mercury vapor lighting systems? — JC, Halifax, Nova Scotia
While incandescent lighting isn’t nearly as energy efficient as those other light systems, it produces a more eye pleasing light than some of the alternatives. Our eyes are optimized for sunlight, so that we find the spectrum of light from hot objects particularly pleasant. The heart of an incandescent bulb is a hot tungsten filament. High-pressure arc lamps such as sodium vapor or mercury vapor lamps (metal halide lamps are just somewhat color-corrected high pressure mercury vapor lamps) produce a much less even spectrum of light. High-pressure sodium vapor lamps are wonderfully energy efficient, but their light is orange or pink. High-pressure mercury vapor lamps are also quite energy efficient, but their light is somewhat bluish. Even metal halide lamps aren’t quite white. The other problem with high-pressure arc lamps is that they take time to warm up and then can’t be restarted until they cool off. They’re best in applications that don’t require them to be turned on or off frequently.
A much better choice, both in terms of energy efficiency and light color, is a fluorescent or compact fluorescent lamp. Such lamps typically use less than 25% of the energy required for comparable incandescent lighting, provide excellent color rendering that can be chosen to match that of incandescent lighting, and they last much longer than incandescent bulbs. Even though compact fluorescent lamps are more expensive than incandescent bulbs up front, they last so much longer and save so much energy that each one typically saves you about $45 over its working life.