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.
Do torchieres distribute light differently?

NLPIP tested one sample of each of six alternative torchieres (described in "What are the alternatives to halogen torchieres?"). NLPIP also tested one halogen torchiere five times, each time with a 300-W halogen lamp from a different manufacturer. NLPIP duplicated a typical application of the torchieres by positioning the torchieres in the corner of a room with a white ceiling and walls. The center of each torchiere was 1.5' (0.4 meters) from the walls. The ceiling was 8' 10" (2.7 meters) high. NLPIP measured illuminance at the points shown in Figure 5. Figure 5 also indicates the range of illuminances that NLPIP measured at some of the points.

Figure 5

In general, the halogen torchiere and the alternatives produced similar light distribution patterns on the walls and floor. Figure 6 shows the typical pattern of illuminance produced by a torchiere in the corner of a room.

Figure 6

NLPIP compared rated light output to ceiling illuminance for the five halogen lamps and six alternatives. For the halogens and three of the alternatives (incandescent A-lamp, quad CFL, and flat CFL), the illuminance on the ceiling was directly related to the lamp's rated light output. In other words, the lamps with higher rated light output illuminated the ceiling more.

However, the long CFL torchiere produced higher illuminances on the ceiling than would be assumed from its rated light output.

The metal halide torchiere produced lower illuminances on the ceiling than might be assumed from its rated light output. It had a translucent shade instead of the usual opaque metal shade with a white interior. The translucent shade transmitted some light directly to the walls and floors rather than reflecting all light toward the ceiling.

The circular CFL torchiere also produced lower-than-expected illuminances on the ceiling. It had a translucent section at the base of the shade, which also transmitted some light instead of reflecting it toward the ceiling. Another possible explanation for this torchiere's low illuminance is that its low active power produces lower-than-rated light output from its lamp (see Table 3).

The rated light output of the five halogen lamps tested in the halogen torchiere varied by 25% (in other words, the lowest rated light output for a halogen lamp was 75% of the highest rated light output). The illuminances provided by the five lamps varied even more: the lowest illuminance at any measured point averaged only 59% of the highest illuminance at that point. These lamps were all tested in the same torchiere, which means that the variation was caused by the light produced by the lamps rather than by the design of the torchiere.

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