This page brings together information about efficient home lighting technologies and answers questions you may have about these technologies. Much of the contents is centered around more efficient forms of lighting such as fluorescent and compact fluorescent, but it will also provide information about other aspects of lighting as well. Information about lighting controls can be found on the home automation page of this site.

Types of Lighting - how the light is produced

There are many kinds of lighting that vary in the way light is produced. The most likely kinds of light you are likely to find useful for your home are described below.

Choosing the right light

When the right amount of light, you need to consider lumens, not watts. Lumens is a measure of the light output and different types of lights will consume different amount of power (in watts) for the same light output. In particular, a fluorescent light will require between one-quarter to one-sixth as much power for the same output in lumens as an incandescent lamp.

Unfortunately, we have grown up thinking of the quantity of light in terms of the number of watts used by a typical incandescent light. Thus, we think of 60, 75, and 100 watt bulbs when we should be thinking (800), 1200 and (1600) lumens. The following table shows the energy consumption and light output for traditional incandescent and compact fluorescent lights. These numbers are approximate and different brands of bulbs will vary, but it gives you an idea of the energy saved. While compact fluorescent bulbs are more expensive to purchase, they will last significantly longer and if you get them on sale they will often be cost effective based solely on bulb life, not even considering the significant savings in energy cost over the life of the bulb.

Power consumption and light output
Watts Incandescent6075100
Watts Fluorescent152027
Lumens Incandescent-1170-
Lumens Fluorescent-1200-

When, Where, and Why to use Compact Fluorescent Lights

Fluorescent and compact fluorescent lights will save significant energy when used in lights that are on for significant periods of time. They are suited less well to lights that are turned on for only a couple minutes at a time (like in a closet). Fluorescent lights can take a minute or so to come up to full brightness, and frequent cycling will reduce their life.

One disadvantage of compact fluorescent lights is that the typical ones purchased at the grocery or convenience store can not be used with a dimmer. Because of the way dimmers work, you should not use them in a fixture that has a dimmer even if you leave the dimmer in its full on position. More recently, compact fluorescents that do work with dimmers have been introduced, but you need to read the package carefully to make sure they will work, and they only work with modern triac based dimmer. Do not attempt to use use these with old rheostat (resistor) based dimming switches.

Compact fluorescent lights are similarly incompatible with many varieties of illuminated light switches. These switches glow when the light is in the off position so that they can be easily found in the dark. Many of these switches work by sending a small amount of current through the load (the light bulb) when the switch is in the off position. This low current loading will significantly reduce the life of a fluorescent bulb.

Cycle life of fluorescents

There is a lot of debate on whether fluorescent lights should be shut off for short periods of time. The consensus is that from an energy perspective, the added power needed to start the light is small enough that total energy consumed is less if you turn off the light even if it will be turned back on in just a few minutes. The disagreement centers around the effect that frequent cycling has on the lifetime of the bulb. I am looking for more authoritative sources so that I can update this discussion, but a few points to consider are:

Color temperature in fluorescent lights

A common complaint regarding the use of older fluorescent lights in the home is that the light produced does not look natural. More specifically, the color of the light is not what one is used to from incandescent lamps, even though the color may be closer to sunlight. The color of light given off by a fluorescent bulb is described by a color temperature, in degrees kelvin. Incandescent lights have a color temperature of approximately 2800°K and are described as warm. Traditional fluorescent lights have a color temperature of around 4100°K, and is considered cool. As a point of reference, sunlight has a color temperature of approximately 6000°K. At first this seems odd that the warmer colors have the lower color temperature; red is a warmer color than blue, yet blue light has higher energy (think of the red flame versus the blue flame on your gas burner). Today, fluorescent bulbs are available with a choice of color temperatures. Those described as warm will have color closer to that of an incandescent lamp.

While color temperature describes the center of the spectrum of color emitted by a lighting source, lighting with the same color temperature can have widely varying spectra. In particular, daylight has a spectrum centered around 6000°K, but it has components or wavelengths of light covering a significantly wider spectrum. This is why colors look better in daylight, than under artificial lighting. The color rendering index expressed on a scale from 0 to 100 describes the ability of a light to bring out the color in objects. More information on color temperature and CRI can be found in the glossaries listed in links at the bottom of this page.

Using dimmers to get just the right amount of light

Modern dimmer switches use a transistor to rapidly turn a light on and off so that current flows through the light on only part of the A/C cycle. This is significantly more efficient than old dimmers which used resistors, and it generates a lot less heat in the switch itself. The use of a modern dimmer switch on an incandescent light will reduce the power used by the light, decrease the temperature of the bulb, and extend the bulb life. However, such a light operating at decreased power will be less efficient at generating light than it would be at full power (e.g. at 50% power, you might output 30% of the lumens you would generate at full power). This reduction in efficiency is due primarily to the efficiency effect in the light bulb itself, with the dimmer contributing only a small amount to the reduction in efficiency.

Dimmers should not be used with fluorescent lights unless the lights have been specifically designed to work with a dimmer. Most fluorescent lights are not designed for such use, and those that are are specifically described as such in their technical documentation.

For more information on lighting

The following sites have interesting information on lighting.

Footnotes: Fluorescent can also be spelled florescent and it is often misspelled flourescent. Those searching for information might be looking for compact flourescent lights, and compact flourescent bulbs.