Most homes use too much energy for lighting. According to the U.S. Energy Information Administration, the average American household uses 1,667 kWh per year for lighting, which amounts to 15.3% of residential electricity use. Ironically, this energy devoted to lighting is used inefficiently, so the usual result is a dim house with dark, depressing corners.
Although many electric utilities have subsidized the cost of bulb swap programs for years, the typical house still has far too many incandescent bulbs. Even people who have swapped their incandencents for compact fluorescent lamps (CFLs) often install their bulbs in terrible fixtures with opaque shades or dark lenses. Fixtures are often installed in awkward spots. The dark corners that are common in a poorly lit house become more noticeable as we all get older; to see well, older people need more light than younger people.
Finally, many houses have too few switches, so that homeowners have to make an all-or-nothing decision about whether to turn on all six bulbs in a track-light fixture.
Once you become aware of some basic lighting principles, you’ll be able to solve the lighting problems in your own home and the homes you build. There’s only one downside to obtaining a lighting education: every time you stay in a hotel room, the bad lighting will drive you crazy.
Lighting designers have their own jargon. They call light bulbs “lamps,” for example, and they call light fixtures “luminaires.”
Lighting designers often tell us that there are four different kinds of light: ambient, task, accent, and decorative.
Ambient light is the soft, general illumination that fills a room and softens shadows.
Task lighting is a focused source of light near a work surface, a countertop, or a book.
Accent lighting is a type of directed illumination used to spotlight an object — for example, a work of art or a houseplant.
Decorative lighting comes from a fixture chosen for its attractiveness — for example, a chandelier. (The purpose of decorative lighting is not so much to provide light as to draw attention to the fixture.)
The last two types of lighting — accent lighting and decorative lighting — fall into the realm of interior decoration. Although accent and decorative lighting can be important, I won’t be discussing them in this article. If you’re a builder, you don’t necessarily have to master the intricacies of accent lighting and decorative lighting. But it is essential that you provide good ambient lighting and good task lighting in every room.
A single fixture is rarely able to provide both ambient and task lighting, so most rooms require several fixtures. It’s no longer acceptable to put a single fixture in the center of the ceiling and call it good.
There are many ways to provide ambient lighting, but the best ambient lighting fixtures are designed to bounce light off the ceiling. This won’t work if your ceiling is finished with stained tongue-and-groove boards; that’s why the best ceilings are finished with white-painted drywall.
Light fixtures that hang a few inches below the ceiling are often designed to send light upwards as well as downwards. This is a good design for an ambient light source. Ambient light can also be provided by fluorescent tubes located in coves, cornices, or ledges.
When it comes to task lighting, the key is to get the light source as close as possible to what you want to see. Task lighting doesn’t have to be bright, but it should be close.
Color rendering index (CRI) and color temperature
Lamps are rated with two numbers related to color. The first is the color rendering index (CRI). The CRI scale goes from 0 to 100. Light sources with a high number render colors more accurately than light sources with a low number. Among the light sources that achieve 100 CRI are noon sunlight and incandescent bulbs. Many fluorescent bulbs have a CRI of 80, which is high enough to render colors accurately.
Lamps are also rated with a temperature rating in degrees Kelvin (K); this indicates the hue of the light source. Sunlight at sunrise, like an incandescent bulb, is considered a warm (orangey) light. (Confusingly, even though it is called “warm,” it is rated with a low number in degrees Kelvin.) Sunlight at noon, like a halogen lamp or some fluorescent lamps, is considered a cool (white or bluish) light; even though it is called cool, it is rated with a high number in degrees Kelvin.
Here are the degrees Kelvin and CRI numbers for a few light sources:
- Incandescent bulbs: 2,700 K, 100 CRI
- Cool white fluorescent tube: 4,100 K, 62 to 80 CRI
- Noon sunlight: 4,500 K to 5,400K, 100 CRI
For thousands of years, people used candles or oil lamps for nighttime illumination. Eventually, most of the world switched to incandescent electric bulbs. All of these light sources — candles, oil lamps, and incandescent bulbs — are on the warm side of the temperature scale. By now, such warm light seems “normal.” But these warm lamps are a poor imitation of sunlight.
Sunlight is on the other end of the degrees Kelvin scale; it’s cool. Once you begin to notice the difference between cool light sources (for example, the light produced by a halogen lamp) and incandescents, you may begin to prefer cool lamps to traditional warm ones.
However, many people have strong opinions in favor of warm lamps. Fortunately, you can buy CFLs in almost any color temperature you want. Try a few different colors to see which color you prefer. If you’re in doubt, you won’t go wrong if you choose a lamp rated at 3,000 K with a CRI of at least 80.
Martin’s Ten Rules of Lighting
1. For now, screw-based CFLs are the best bulb choice for residential lighting. Bulbs with an Energy Star label are likely to last longer than cheaper unlabeled bulbs.
If LED lamps continue to drop in price and improve in quality, they are (eventually) likely to replace CFLs in many locations. If you care about energy efficiency, use linear fluorescent tubes (especially T-5 or T-8 lamps) in locations where they make sense, like kitchens. Don’t install any incandescent lamps.
Here is some information on lamp efficiency:
- Indancescent bulbs produce about 14 to 17 lumens per watt.
- Low-cost LEDs produce about 15 to 25 lumens per watt.
- High-quality LEDs produce about 40 to 70 lumens per watt.
- CFLs produce about 48 to 60 lumens per watt.
- T-5 and T-8 linear fluorescent tubes produce about 98 to 105 lumens per watt.
2. It’s better to illuminate the ceiling than the floor. The U.S. is cursed by a plague of senseless recessed can fixtures. If you walk under a recessed can, it will cast strange shadows on your face. Why do people like these ridiculous fixtures?
Recessed cans do a great job of illuminating the floor, but they keep your ceiling dark. Some hotels use recessed cans to illuminate their hallways. As you walk down the hallway looking for your room, only one thought is going through your mind: “Ugly carpet. Ugly carpet.”
A good ambient lighting fixture works on a different principle from a recessed can fixture. If you use an ambient lighting fixture to bounce light off a white-painted ceiling, your ceiling will be brighter than your floor. This mimics the natural world; a bright sky makes us cheerful and optimistic. On the other hand, the combination of a bright floor and a dark ceiling feels ominous and unsettling.
Some people assert that recessed can lights can be used for task lighting, but I disagree. The ceiling is too far away from any task; that’s why you need a pendant fixture or a wall-mounted swing-arm fixture for task lighting. The amount of light striking an object is inversely proportional to the distance from the light source squared. If you double the distance, you get only one-fourth as much light. If a lamp produces 64 lumens at 1 foot, it will produce only 16 lumens at 2 feet, and only 4 lumens at 4 feet. At 8 feet, you are down to 1 lumen.
The farther away your light source, the brighter it has to be to be useful. That’s why the worst imaginable fixtures are recessed cans in a high cathedral ceiling.
3. Most homes need more task lighting. Almost every room needs at least one, and often several, task-lighting fixtures. Providing more lighting options usually saves energy. In an office, the most important light fixture is the task light over the desk. An adjustable desk lamp is fine; if you prefer a pendant, bring it low, close to the work surface. Remember: the closer the lamp to the work surface, the fewer lumens you need.
4. Every section of kitchen countertop needs task lighting. Such lighting can be provided by undercabinet lighting attached to the wall cabinets or by small pendant fixtures. Install them lower than you think. As long as the pendants don’t interrupt views through windows or across your kitchen, install them at eye level.
5. Task lighting fixtures should be controlled by separate switches rather than a single switch that energizes several fixtures at once. All-or-nothing switches that control several lamps at once are infuriating. To save energy, it’s important to be able to control your lamps individually.
Resist the temptation to locate all of a room’s switches in one location. Four switches all in a row are confusing. It’s better to scatter the switches around the room; most switches should be located near the fixture that the switch controls.
6. Put reading lights where they belong. A reading light should be close to your book or magazine. In general, the light should come from over your shoulder or from the wall above the back of your head. A short table lamp on a low coffee table at the end of the sofa won’t work; the light will be too low. Task lighting for reading should be provided for every piece of furniture in your living room. There shouldn’t be any armchair or any seat on a sofa where the lighting is insufficient for reading. In bedrooms, the best location for a reading light is on the wall above the headboard of your bed.
7. Most bedrooms have insufficient ambient light. If you’re reading in bed, you don’t really need any ambient light. But when you are getting dressed or packing a suitcase, you need plenty of ambient light. If your bedroom has insufficient ambient light, it’s hard to find things.
8. Every bathroom needs at least two wall-mounted fixtures, located to the right and to the left of the bathroom mirror. If the light source is above the mirror, it can cast shadows on your face. Again, when fixtures are located in the right place, they can use bulbs of a lower wattage than are required for poorly placed fixtures.
9. Just say no to dark-colored shades and lenses. Evidently Jesus had a good grasp of lighting principles, because in Matthew 5:15 he gave excellent advice: don’t hide your lamp under a bushel basket, but put it on a lamp-stand. Unfortunately, far too many people hide their lamps behind dark-colored lenses or brown lampshades (the bushel baskets of our era). Since you want the maximum number of lumens per watt, it makes little sense to produce a bright light and hide it behind a filter that obscures 80% of the lamp’s output.
Choose fixtures with clear lenses, if possible. Don’t be afraid of fixtures with a modern design that incorporate a bare lamp.
10. Don’t forget to provide good lighting in basements, attics, and crawl spaces. You need more fixtures than you think, so provide lots of them. Remember to provide a separate switch for each fixture.
Last week’s blog: “Keeping Ducts Indoors.”