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
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.
- Incandescent lights work by passing electric current through a
wire which gets hot and gives off light. Traditional light bulbs are
incandescent. They are inexpensive, but they are inefficient using
much of the energy consumed to produce heat.
- Fluorescent lights work by passing electrons through a
gas in a sealed tube. The gas contains a small amount of mercury
which is excited, which gives off light when the mercury returns to an
unexcited state. This light is absorbed by a phosphor coating on the
bulb which then gives off visible light. Fluorescent bulbs produce
four to six times as much light as an incandescent for the same power
consumed. They typically cost more, but last longer and the extra
cost if made up many times over by the energy savings. Most
fluorescent lights can not be used with a dimmer (even in the
- Compact Fluorescent lights are Fluorescent lights designed
to fit in the socket for a standard incandescent bulb. They work the
same way, and have the same advantages as a Fluorescent light.
- Halogen lights are a form of incandescent light where a
tungsten filament is surrounded by a halogen gas in a quartz tube.
Halogen lamps burn hotter and brighter than a traditional incandescent
bulb and they last longer. While such bulbs are more efficient in the
sense that they consume less power per lumen output, they are often
used in a way that is less efficient, providing significantly more
light than is needed. The higher temperature can also create a fire
or burning hazard.
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
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:
- It can take a couple minutes for a fluorescent light to reach full
brightness once it is turned on. If you require full brightness,
frequent cycling will affect the light output during the first couple
of minutes of each cycle.
- One source I found indicated that the wear-and-tear on the bulb
from cycling it off and on is equivalent to about 20 minutes of actual
use. I do not know if I believe this assessment because I believe that
the wear-and-tear on the bulb from cycling is primarily to the
ballast, whereas the wear-and-tear from continued use is primarily to
the phosphors, meaning that one can not trade-off one for the other.
- Please let me know if you come across a source with solid data that answers this question.
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
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
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.