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.
Why are halogen torchieres so popular?

Halogen torchieres are popular with consumers because of their appearance, light distribution, versatility, availability, and cost. Torchieres provide indirect lighting, which means they illuminate spaces by reflecting light off ceilings and walls. They are an inexpensive source of indirect lighting that does not require an electrician to install. Their slim, upright design helps them fit into almost any decor. Torchieres make it possible to change the ambiance within a space by moving the torchiere or dimming the lamp. They are lightweight and can be easily moved from room to room. Halogen torchieres are often sold with continuous dimming, or  bilevel or trilevel switching.

Light from undimmed halogen lamps has a correlated color temperature (CCT) of approximately 3000 kelvin (K)--slightly higher (more white) than the incandescent A-lamps used in most residential luminaires--and a color rendering index (CRI) of 95+. Dimming a halogen lamp reduces the CCT of the light, making it appear warmer (more yellow) and more like that of incandescent A-lamps.

Ninety percent of the halogen torchieres sold in the United States have 300-watt halogen lamps. Halogen torchieres have been widely available for years at department stores, lighting distributors, home improvement centers, and other retail outlets at prices as low as $10 to $15.

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