Volume 11 Issue 1
May 2010    
LED Residential Under-cabinet Luminaires
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. lamp rated life - The number of operating hours at which half of a large group of product samples are expected to fail. The rated life is a median value of life expectancy; individual lamp life may vary considerably from the published rated life and operating conditions (e.g., temperature, hours per start) may affect actual life because rated life is based on standard test conditions. In addition, the way a product fails can vary by technology. For example, incandescent lamps abruptly stop producing any light while LEDs are considered to have failed when their light output drops below a certain fraction of the initial level. 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. power - The power used by a device to produce useful work (also called input power or active power). In lighting, it is the system input power for a lamp and ballast or driver combination. Power is typically reported in the SI units of watts. luminous flux - Luminous radiant power, measured in lumens. The overall light output of a lamp or luminaire. uniformity - The degree of variation of illuminance over a given plane. Greater uniformity means less variation of illuminance. The uniformity ratio of illuminance is a measure of that variation expressed as either the ratio of the minimum to the maximum illuminance or the ratio of the minimum to the average illuminance. lux (lx) - A measure of illuminance in lumens per square meter. One lux equals 0.093 footcandle. 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. Models are listed first by light source, then alphabetically by brand, then by model number.
How uniform is the light produced by LED under-cabinet luminaires?

The IESNA recommends that the illumination in the area immediately surrounding the task area not be five times greater than or less than one fifth the illumination in the task area itself. ASSIST recommends suggests evaluating this uniformity ratio by comparing the average illuminance of the entire application area with the minimum value found on the application area. This average:minimum illuminance ratio should not exceed 5:1. Good uniformity (a ratio less than 5:1) improves visual comfort and reduces shadows.

Table 4 shows the uniformity for the under-cabinet luminaires that NLPIP measured. The lower the ratio in the uniformity column, the better. Table 4 also includes plots of the illuminance on the horizontal application (countertop) area. The steeper the surface, the lower the uniformity. All of the luminaires had a uniformity ratio less than the recommended 5:1 except the GE 10136 (xenon incandescent), which slightly exceeded it. NLPIP found that all of the luminaires provided adequate uniformity, which can be further improved by installing multiple luminaires next to one another so their areas of illumination overlap.

Table 4. Uniformity of lighting within the application area on a horizontal surface.
Light source Brand Model Uniformity on horizontal application area Uniformity distribution
LED GE 10408 2.4:1 GE 10408 - click for larger image
GE 10409 3.0:1 GE 10409 - click for larger image
Utilitech 283278 3.3:1 Utilitech 283278 - click for larger image
Utilitech 283520 3.1:1 Utilitech 283520 - click for larger image
Fluorescent GE 10113 3.5:1 GE 10113 - click for larger image
Utilitech 069486 4.4:1 Utilitech 069486 - click for larger image
Xenon (incan-descent) GE 10136 5.9:1 GE 10136 - click for larger image
Utilitech 283542 3.3:1 Utilitech 283542 - click for larger image


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