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 energy-efficient are LED under-cabinet luminaires?

Many people are interested in LEDs as a technology with the potential to reduce energy use and perhaps save money as a result. As an aid in determining which products use the least amount of energy, application efficacy describes how much light reaches the application area per unit of electrical input power. Application efficacy considers only the luminous flux falling on the application area, as defined in the Introduction, and disregards light falling on other areas, thus giving “useful light” per watt.

The last column of Table 5 shows the application efficacy of the under-cabinet luminaires tested by NLPIP. The higher the efficacy, the better. The luminous flux falling on the application area includes both the horizontal and vertical surfaces (the countertop and backsplash) in this analysis.

Table 5. Application efficacy of under-cabinet luminaires.
Light source Brand Model Power,
measured (W)
efficacy (lm/W)
LED GE 10408 5.24 22.3
GE 10409 6.20 29.0
Utilitech 283278 7.03 24.9
Utilitech 283520 1.19 38.8
Fluorescent GE 10113 12.2 24.6
Utilitech 069486 15.0 17.4
Xenon (incandescent) GE 10136 46.3 5.8
Utilitech 283542 61.6 3.6

The average application efficacy of the four LED luminaires was 28.8 lm/W, compared with an average 21.0 lm/W for the two fluorescent luminaires. The LED luminaires had a wide range of efficacies, illustrating that using an LED light source does not itself guarantee a highly efficacious luminaire. The two luminaires with xenon light sources averaged 4.7 lm/W, well below the LED and fluorescent luminaries.

Figure 2 shows the relationship between application efficacy and illuminance identified by light source type. As noted in the section, “How much light do LED under-cabinet luminaires produce?” NLPIP found that the luminaire with the highest application efficacy, the Utilitech 283520, provided less illumination than that recommended by McGuiness and Boyce (1984).

Figure 2. Application efficacy vs. horizontal illuminance
of under-cabinet luminaires.

Test apparatus drawing

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