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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.
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 replace bulbs.
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 300-500 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
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 affect actual light output.
Comparison of typical bulbs
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 85-95. Older fluorescents will typically have a CRI in the 60ís.