Undercabinet lighting is potentially a good application for LEDs (see solid state lightning), taking advantage of their directionality and small size. This section looks at undercabinet specifically for residential kitchens, and presents information on the performance of several LED fixtures suited for this application.

 

Overview of kitchen undercabinet lighting

Undercabinet lighting is used in kitchens to provide task lighting and to supplement the overall ambient lighting for the space. Undercabinet lights illuminate the horizontal task surface used for food preparation, reading cookbooks and food packages, cooking, and clean-up, and provide vertical illuminance on the wall behind the counter. Color temperature for residential kitchens is typically 3000K or lower, providing a warm look. Color rendering is important for evaluation of the appearance of food, for social interaction, and for complementing decorative finishes used in kitchens. The task plane is typically 20 to 22 inches in depth and the length varies in relationship to the upper and lower cabinets. Uniform illumination is important to prevent shadows and give the perception of a larger space.

 

Typical fixtures designed for use with halogen or fluorescent sources range from about 30% to 50% efficient, which means that half or more of the light produced by the lamps never leaves the fixture. The inherent directionality of LEDs can provide a distinct advantage, allowing them to compete with traditional light sources in this application. The table below presents energy and light output data for several traditional fixtures, two currently available LED-based undercabinet fixtures and one LED-based prototype. The LED fixtures tested are all more efficacious than halogen, and two of the three are approximately the same or more efficacious than the fluorescent fixture, on a luminaire basis.

 

Potential for use of LEDs in kitchen undercabinet lighting

LEDs are a natural fit for undercabinet lighting. The ability to string LEDs in a linear array or to cluster them in a puck-like fashion provides options to lighting designers to imitate the form factor of linear fluorescent lamps or the single lamps of a halogen or xenon fixture. The efficacy of newer high-flux LEDs is approaching that of fluorescent lamps with a wider choice of color temperatures available. The inherent directionality of LEDs allows a larger proportion of the available light to be directed where it is needed and not lost within the fixture.

 

Typical fixtures designed for use with halogen or fluorescent sources range from about 30% to 50% efficient, which means that half or more of the light produced by the lamps never leaves the fixture.

 

The table below presents energy and light output data for several traditional fixtures and two currently available LED-based undercabinet fixtures.

 

Examples of undercabinet lighting performance using different light sources
	Incandescent halogen1	Fluorescent*	LED 1*	LED 2*2	LED 3*
CCT	3000K	3015K	2767K	3328K	3552K
CRI	100	84	70	83	71
Luminaire lumens	440	689	265	758	344
Luminaire watts	60	19	8.7	21	8
Luminaire length	1.91 ft.	3 ft.	2 ft.	1.4 ft.	1.8 ft.
Lumens per linear foot	230	230	133	527	194
Luminaire efficacy (lm/W)	7	36	31	36	43

 

1 Based on photometric data for commonly available products. Actual product performance depends on reflectors, trims, lamp positioning, and other factors. Assumptions available from PNNL.
* Based on photometric testing of CFL and LED undercabinet fixtures July 2007. Except as noted, fixtures tested were purchased through normal market channels.
2 This sample was a prototype submitted by the manufacturer.

 

Luminaires for undercabinet applications are usually linear in design although "puck" style products are available as well. Luminaires were compared on a per-linear foot basis as products are sold in varying lengths with varying light outputs. Compared to the traditional fixtures, the LED fixtures provided equivalent or more lumens per linear foot. One of the LED fixtures produced more than two times the lumens per linear foot than the traditional fixtures. The bottom line of the table shows LED luminaire efficacy similar or better than the high performing fluorescent fixture. The three LED fixtures all have similar CCTs to both the halogen and the fluorescent fixtures although their CRIs are lower. One important caveat: lumen depreciation (useful life) data is not presently available for LED luminaires.

 

Comparing LED kitchen undercabinet lighting to traditional light sources

Although originally intended for directional lighting, recessed downlights are now used widely for general ambient lighting in kitchens, hallways, bathrooms, and other areas of the home. Other types of downlights using spot lamps, reflectors, and lenses are also used for art, accent, display, and wall lighting. In some applications, like media rooms and dining areas, downlights are operated on dimming circuits. The most common light source used in residential downlights is a 65-watt incandescent reflector-style lamp with a standard Edison base. Other commonly used options include A-type incandescent lamps, and PL-type, spiral, or reflector CFLs.

 

The light output of a traditional recessed downlight is a function of the lumens produced by the lamp and the luminaire (fixture) efficiency. Reflector-style lamps are specially shaped and coated to emit light in a defined cone, while "A" style incandescent lamps and CFLs emit light in all directions, leading to significant light loss unless the luminaire is designed with internal reflectors. Downlights using non-reflector lamps are typically only 50% to 60% efficient, meaning about half the light produced by the lamp is wasted inside the fixture. Recently, LED downlights have come on the market. Table 1 provides examples of performance data for residential recessed downlight using several different light sources, including two LED products. These data should not be used to generalize the performance of fixture types, but are provided as examples.

 

Evaluating current LED undercabinet luminaires

LED undercabinet fixtures are more expensive than most other fixtures, but they continue to improve in performance as well as price. As new LED-based undercabinet lights enter the market, users should keep the following in mind:

 

LED luminaires must be engineered to mitigate heat. This can be accomplished by adding heat sinks or utilizing the fixture chassis as a heat dissipation mechanism.

Beam patterns must be considered; the luminaire should provide uniform illumination, both on the horizontal and vertical surfaces.

Although LED color quality continues to improve, individual products should be evaluated carefully. Some commercially available products have very high color temperature (i.e., the light appears blue/cool), noticeable color variations across the product, and/or very low color rendering.

Some LED undercabinet luminaires have excessive shadowing caused by the arrangement of the LEDs in the fixture. This can be distracting depending on the type of task surface and is most noticeable on single-color, matte finishes.