Compact Fluorescent Lamps
Measuring Light Output and Usage
Comparison of Typical Bulbs
All of us are familiar with the standard incandescent light bulb that is used in most
light fixtures today. Most people are also familiar with 4-foot and 8-foot linear
fluorescent lights that are common in schools and offices. However, several types of
energy-efficient bulbs are gaining in popularity; most of these have been around for years
and are standard throughout Europe.
|Compact Fluorescent Lamps
Compact fluorescent lamps use roughly 75% less energy than incandescent
bulbs and last 10 times as long. They have a high purchase price (typically $15 each), but
the energy savings are substantially more than this. A 23-watt compact fluorescent lamp
used in place of a 90-watt incandescent bulb will produce the same amount of light and
save 670 kWh over its lifetime. This amounts to roughly $58 in electricity savings at
average national prices from the purchase of a $15 bulb. Compact fluorescents should not
be confused with older styles of fluorescent lighting which had a tendency to buzz or
flicker; compact fluorescent lights have largely overcome these problems. Unfortunately,
compact fluorescent bulbs may not fit in all fixtures because they are usually a little
larger than a standard incandescent bulb. However, adapters are available that enable
compact fluorescent lamps to fit in most fixtures, and new fixtures designed specifically
for these bulbs are also on the market.
EnergyMiser, or Supersaver bulbs are incandescents that use 5% to 13% less electricity
than ordinary light bulbs with only a very minimal reduction in light output. They cost
slightly more, but are economical on a lifetime basis. Donít confuse these with
Longlife bulbs, which can last up to twice as long, but are less efficient than standard
bulbs. Longlife bulbs are generally recommended in locations where it is difficult to
Halogen bulbs are more efficient than standard incandescent bulbs and last three to
four times as long. Replacing incandescent track and spot lighting is the best application
for halogen bulbs; you can use a lower wattage bulb and get the same general effect as
with larger wattage incandescents. This also holds true for outside flood lights. However,
be wary of high wattage halogen lamps, sometimes in the 300 to 500 watt range. These
produce a tremendous amount of light but consume an equally large amount of energy. You
should also be aware that there are serious safety concerns over very popular halogen
torchiere-style floor lamps. These fixtures generate intense heat and can cause fires if
placed too close to flammable materials.
Measuring Light Output and Usage
Most people readily associate the term wattage with lights, but mistakenly assume it is a
measure of the amount of light produced. Wattage is actually a measure of the energy usage
of the bulb. The light output of a bulb is measured in lumens. A bulb with a lower wattage
can actually have a much higher lumen output. Lighting packaging today must indicate the
lumens produced by a bulb.
Improving the efficiency of a bulb requires using less energy (watts) for a given level
of light output (lumens). A common measure of the efficiency of a bulb, termed efficacy,
is lumens divided by watts. The cost-effectiveness of a bulb also takes into account its
cost and life. A comparison of typical bulbs appears below. Be aware that these are
representative only; there are variances among specific bulbs, and other factors,
including light fixtures, bulb placement, and age of bulb, will effect actual light
Comparison of typical bulbs
|flood: 75 (760)
Notice, for example, that a 52-watt Energy Miser bulb uses about 13% less energy than
its 60-watt incandescent counterpart, but in turn produces over 90% of the light. A
comparable long life bulb, however, while lasting 2.5 times as long, will only produce
about 82% of the light of the incandescent. On the other hand, a 13-watt Compact
Fluorescent produces the same light as the 52-watt Energy Miser but uses only 25% of the
energy and lasts 10 times as long. Even given its higher cost, such a bulb would cost
approximately $28 dollars over its life vs. $72.50 for an incandescent (using a cost per
kWh of 10 cents).
Effective May 1995, all bulb manufacturers had to re-label their products under Federal
Trade Commission consumer protection regulation. The new labels must provide the light
output (measured in lumens), the amount of energy used (watts); and the lifetime (hours).
If positioning affects a compact fluorescentís light output by more than 5% (see
discussion below) that must be disclosed.
Light quality is measured in Color Rendering Index (CRI) and Correlated Color
Temperature (CCT). CCT, which is measured on the Kelvin (deg.K) temperature scale,
provides an indication of how the light will look. Cooler lights (those with more blue)
are those with higher temperatures; a CCT higher than 2,800 typically indicates a cooler
light and will look whiter than a standard incandescent. Bulbs with CCTís below 2800
will appear more red in nature.
CRI is a measure of how objects will look under the light. It is roughly a comparison
of the light source with natural light, with a CRI of 100 the equivalent of natural light.
CRI for a standard incandescent will be in the range of 85 to 95. Older fluorescents will
typically have a CRI in the 60ís.