Lighting Research Center Lighting Research Center
    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 much light do LED under-cabinet luminaires produce?

Under-cabinet luminaires serve two general functions in the kitchen. First, under-cabinet luminaires can provide a sense of brightness for the homeowner without raising overall ambient light levels. Second, under-cabinet luminaires provide illumination for tasks performed on the counter, such as reading a recipe or chopping food. How much illumination is needed? The Illuminating Engineering Society of North America (IESNA) Lighting Handbook, 9th Edition (Rea 2000) recommends minimum illumination levels of 300 lux for general tasks and 500 lux for critical tasks such as chopping. However, McGuiness and Boyce (1984) found that an illumination level of 100 lux was sufficient for people to perform all kitchen tasks quickly and to feel satisfied with the light level.

The test apparatus, which simulates the geometry of a kitchen countertop and back splash, has black, non-reflective surfaces so as to measure only direct illumination. In an actual kitchen, a small amount of the light shining on the backsplash will be reflected onto the horizontal application surface, which gives the countertop additional lighting. This study purposely does not account for this additional light because backsplashes vary greatly from kitchen to kitchen. When NLPIP investigators covered the vertical back splash area with matte white paper for one LED luminaire, the average horizontal illuminance increased by 5%.

The Utilitech 283542 can be turned on to a high or low setting, and it can swivel forward and back. For these tests, it was turned to the highest light output setting and was swiveled so the bottom of the luminaire was horizontal, presumably indicating that the light was aimed directly downward.

As shown in Table 3, all but one luminaire (the Utilitech 283520) provided at least the light level recommended by McGuiness and Boyce (1984) and would provide sufficient illumination for kitchen tasks. If there were a high ambient light level in the kitchen added to the illumination from the Utilitech 283520, then the total could reach the recommended level, but often a person is shading the countertop from ambient light when standing at the counter. Therefore, NLPIP recommends using luminaires that provide more illumination than produced by this model when task illumination is a priority.

Table 3. Luminous flux and illuminance on horizontal surface
provided by under-cabinet luminaires.
Light source Brand Model Luminous flux (lm) Illuminance on horizontal application area (lux)
Horizontal application area Vertical application area Total Average Maximum
LED GE 10408 82.5 34.4 117 148 265
GE 10409 127 51.0 178 186 360
Utilitech 283278 115 77.7 175 169 331
Utilitech 283520 30.7 15.3 46.0 45 92
Fluorescent GE 10113 141 159 301 207 415
Utilitech 069486 110 151 261 162 354
Xenon (incandescent) GE 10136 222 45.8 267 325 747
Utilitech 283542 157 65.8 223 230 449

 

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