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.
Will LED under-cabinet luminaires be cost effective?

Table 6 provides a calculation of the total cost of ownership of the under-cabinet luminaires using the following assumptions:

  • Duration of installation = 10 years
  • Cost of electricity = $0.1136/kWh (U.S. DOE)
  • Time of operation = 3 hours/day
  • LED luminaire life > 11,000 hours
  • Fluorescent lamp life = 7,500 hours
  • Xenon lamp life = 8,000 hours
  • Fluorescent lamp replacement cost = $4.80
  • Xenon lamp replacement cost = $3.60
  • Installation time for lamps that come with a plug (the LED and xenon models) = 0.5 hour
  • Installation time for lamps that come with a wire lead (the fluorescent models) = 1.0 hour
  • Installation labor rate = $56/ hour

For the purposes of this economic analysis, the lifetime of the LED luminaires was assumed to be 11,000 hours or greater, meaning that the initial luminaire would last for at least 10 years. (Testing the actual lifetime of the under-cabinet luminaires was beyond the scope of this project.) The lamp life and lamp replacement cost of the fluorescent and xenon models and the installation labor rate are the values used in ASSIST recommends Volume 2, Issue 1: A Homeowner's Guide to Residential Under-cabinet Lighting: Getting Good Lighting for Your Kitchen Counters. The installation times are estimates based on NLPIP’s experience installing these models for testing. These calculations use a simple cost analysis and do not include adjustments for the time value of money or inflation.

Table 6. Under-cabinet luminaire cost of ownership over 10 years.
Light source Brand Model Initial price ($) Initial installation labor cost ($) Cost of electricity ($) Lamp replacement cost ($) Total cost of ownership ($)
LED GE 10408 55 28 7 0 90
GE 10409 65 28 8 0 101
Utilitech 283278 59 28 9 0 96
Utilitech 283520 25 28 1 0 54
Fluorescent GE 10113 26 56 15 5 102
Utilitech 069486 17 56 19 5 96
Xenon (incandescent) GE 10136 47 28 58 4 136
Utilitech 283542 35 28 77 4 143

The cost of ownership results are plotted in Figure 3 along with each luminaire’s light output. The lower the cost of ownership, the better.

Figure 3. Cost of ownership over 10 years vs. light output
of under-cabinet luminaires.


Cost of ownership vs. light output

The luminaire with the lowest cost of ownership, the Utilitech 283520, provides less illumination than that recommended by McGuiness and Boyce (1984). The fluorescent luminaires have approximately the same cost of ownership as the other LED luminaires. However, the fluorescent models provide more light.

If the LED luminaires were to fail sooner than the assumed 11,000 hours of life, requiring that the entire luminaire be replaced, then their costs of ownership would be significantly higher than the fluorescent models and would approach those of the xenon models, which have high costs of ownership due to greater electricity use.

Previous
Previous
© 2010 Rensselaer Polytechnic Institute. All rights reserved. Next Next


Rensselaer Polytechnic Institute
LRC Intranet Web mail Lighting Research Center