Volume 9 Issue 3
May 2000    
A-lamp - The incandescent lamp most commonly used in North American households. The "A" designation refers to the lamp's bulbous shape. ballast - A device required by electric-discharge light sources such as fluorescent or HID lamps to regulate voltage and current supplied to the lamp during start and throughout operation. bi-level switching - Control of light source intensity at two discrete levels in addition to off. compact fluorescent lamp (CFL) - A family of single-ended fluorescent-discharge light sources with small-diameter [16-millimeter (5/8-inch) or less] tubes. continuous dimming - Control of a light source's intensity to practically any value within a given operating range. tri-level switching - Control of light source intensity at three discrete levels in addition to off. indirect lighting - Light arriving at a surface after reflecting from one or more surfaces (usually walls and/or ceilings) that are not part of the luminaire. lamp - A radiant light source. luminaire - A complete lighting unit consisting of a lamp or lamps and the parts designed to distribute the light, to position and protect the lamp(s), and to connect the lamp(s) to the power supply. (Also referred to as fixture.) correlated color temperature (CCT) - A specification for white light sources used to describe the dominant color tone along the dimension from warm (yellows and reds) to cool (blue). Lamps with a CCT rating below 3200 K are usually considered warm sources, whereas those with a CCT above 4000 K usually considered cool in appearance. Temperatures in between are considered neutral in appearance. Technically, CCT extends the practice of using temperature, in kelvins (K), for specifying the spectrum of light sources other than blackbody radiators. Incandescent lamps and daylight closely approximate the spectra of black body radiators at different temperatures and can be designated by the corresponding temperature of a blackbody radiator. The spectra of fluorescent and LED sources, however, differ substantially from black body radiators yet they can have a color appearance similar to a blackbody radiator of a particular temperature as given by CCT. direct light - Light emitted by a luminaire in the general direction of the task to be illuminated. The term usually refers to light emitted in a downward direction. halogen lamp - An incandescent lamp that uses a halogen fill gas. Halogen lamps have higher rated efficacies and longer lives than standard incandescent A-lamps. active power - the system input power (in watts) for a lamp-ballast combination. color rendering index (CRI) - A rating index commonly used to represent how well a light source renders the colors of objects that it illuminates. For a CRI value of 100, the maximum value, the colors of objects can be expected to be seen as they would appear under an incandescent or daylight spectrum of the same correlated color temperature (CCT). Sources with CRI values less than 50 are generally regarded as rendering colors poorly, that is, colors may appear unnatural. efficacy - The ratio of light output (in lumens) to input power (in watts), expressed as lumens per watt (LPW). illuminance - The density of luminous flux incident upon a surface. Illuminance is measured in footcandles (lumens/square foot) or lux (lumens/square meter). One footcandle equals 10.76 lux. lamp life - The number of hours at which half of a large group of lamps have failed when operated under standard testing conditions. lumen (lm) - A unit measurement of the rate at which a lamp produces light. A lamp's lumen output rating expresses the total amount of light the lamp emits in all directions per unit time. metal halide lamp - A high-intensity discharge (HID) lamp that uses mercury and several halide additives as light-producing elements. Metal halide lamps have better color properties than other HID lamp types because the different additives produce light distributed over more visible wavelengths, resulting in a more complete spectrum. Metal halide lamps are available with CCTs from 2300 to 5400 K and with CRI values from 60 to 93. Efficacies of metal halide lamps typically range from 75 to 125 LPW.
What problems are attributed to halogen torchieres?

Three-hundred-watt halogen lamps reach operating temperatures high enough to ignite paper, cloth, wood, or plastic that is tossed into, blown into, or draped over the lamp. In some cases, fires have started when torchieres have fallen over and touched carpet, drapes, or bedding. NLPIP measured temperatures in torchieres containing halogen, fluorescent, incandescent, and metal halide lamps, as shown in "How hot are the torchieres?".

Ecos Consulting examined data from the United States (U.S.) Consumer Product Safety Commission (CPSC), insurance companies, law firms, and newspapers. By August 1999, Ecos attributed 350 fires to halogen torchieres, resulting in 30 deaths, 114 injuries, and $2 million in damage (LightSite 1999). As a result of potential fire hazard, halogen torchieres have been banned in dormitories by two-thirds of the colleges and universities in the U.S. (Calwell et al. 1998).

In 1996, Underwriters Laboratories (UL) withdrew its listing for halogen torchieres with 500-W lamps to reduce the risk of fire. They urged consumers to replace 500-watt (W) lamps with 300-W lamps. UL also tightened its safety requirements for halogen torchieres in 1997 and again in June 1999 (Underwriters Laboratories 1999). See "New UL Requirements" for examples of the new safety requirements.

When tubular halogen lamps fail, they sometimes explode or shatter. Careful handling is required because oils from the skin make the lamps susceptible to shattering while operating. For this reason, a tempered glass "shatter shield" is required in halogen torchieres to enclose any fragments of hot quartz glass that can scatter on nearby combustibles. This shield closely covers the lamp and offers very little heat protection. The shatter shield should be reinstalled every time the lamp is replaced. Unfortunately, some consumers disregard this precaution.

In addition, halogen lamps might not provide the energy savings that are sometimes advertised for them. Although some halogen lamps provide 18-20 lumens per watt (LPW), Siminovitch and Page (1997) found that the average imported halogen lamp produced less than 12 LPW--40% less than a 100-W A-lamp.

Dimming further reduces the efficacy of halogen lamps to as low as 2 LPW. Figure 3 illustrates that a halogen lamp dimmed to 50% of maximum light output still requires 73% of the active power it requires at 100% output. Another way to consider dimming efficacy is that when active power is reduced to 50%, the lamp produces only 20% of its maximum light output.

Figure 3
Although halogen torchieres are inexpensive to buy, operating cost makes them more expensive overall than most energy-efficient luminaires. The electricity costs of operating a halogen torchiere can be quite high, about $44 per year (assuming a 300-W lamp, operated for four hours every day, at 10¢ per kilowatt-hour). See "How much do the torchieres cost?" to compare the operating costs of halogen and alternative torchieres.

Consumers may also try to use the torchieres for reading, craft work, or other tasks best performed under direct light, and find them inadequate. Torchieres must produce relatively high light levels on the ceiling before enough light becomes available for these tasks. High or dark ceilings and walls further reduce the light available on task surfaces. Desk lamps or even table lamps with much lower-wattage lamps save energy and provide more appropriate task lighting.

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