Under-cabinet LED lights

My parents moved to a new house this year and got, for the first time, under-cabinet lighting to illuminate the countertops in the kitchen.  The original fixtures contained about 360 W of incandescent lighting.  To address problems including heating and uneven lighting, and to reduce electricity consumption, I made and installed white LED lights.  The new lights are cooler, draw less power, and provide more even lighting.

The original under-counter lights installed in my parents' house consisted of seven fixtures holding a total of eighteen twenty-Watt bulbs.  We all agreed that having such direct lighting of the counters is great for working in the kitchen, but several problems quickly became apparent:

• The seven discrete light fixtures provide uneven illumination of the countertops.
• The heat generated by the lights was a problem in some places.  Two of the lights have to be kept off because wine is kept in cubbyholes immediately above them, and if the lights are left on for any length of time the wine gets rather hot.  (None of us are exactly wine connoisseurs, but we do know that wine isn't supposed to be stored in an incubator!)  The spices, in another cabinet, also got overly warm.
• With all the lights on, the under-cabinet lights drew about 360 W of power.  Compact fluorescent light bulbs are used elsewhere in the house, and I doubt that 360 W worth of lighting is in use in the entire rest of the house at any one time.  To use so much power to light just the kitchen counters seemed excessive.

To solve these problems, I made some LED lights and installed them to light the kitchen counters.  Each light is based on a powder-coated aluminum baseplate that I had made through eMachineShop.  The LED is a Cree XP-G warm white LED on an Indus Star PCB and is held in place on the baseplate with a BJB solderless connector.  I got both of those parts through LEDSupply.

I first made some very small baseplates, thinking that they would be mounted inside the existing light fixtures and that the fixtures would serve as heat sinks.  Later, we decided to evenly space the lights under the cabinets, which made placing them inside the existing fixtures impossible, so I had larger baseplates made.  (Both are shown in the photo at right.  Click on any photo to see the full-size version.)  To make sure the LEDs were not overheating, I made a temperature logger using an Arduino Leonardo, k-type thermocouple, and MAX6675 thermocouple amplifier, all from SparkFun Electronics.  When placed on the larger baseplate and mounted under a cabinet, the PCB adjacent to the PCB does not get to much over 40 °C.  The heat flux into the baseplate from the bottom of the PCB is fairly low, and it did not prove necessary to do anything special at the interface between the two.  Adding a dab of thermal grease under the PCB reduced its steady-state temperature by about two degrees, and removing the powder coating from the baseplate reduced the PCB temperature by an additional degree or so.  Since I had the grease anyway, I went ahead and used it, but removing the powder coating was not worth the trouble.  From my reading of the LED and PCB datasheets, I expect the LED junction to be perhaps 5 - 10 °C warmer than the temperatures I measured, which for these LEDs is nice and cool.  I expect the lights to last for a long time.

I mounted the lights spaced evenly under the cabinets using small wood screws and the mounting holes in the baseplates.  I placed the lights near the front of the cabinets to get them as close to centered over the counters as possible.  (In contrast, the original lights were mounted against the backs of the cabinets, so that more of their light was emitted onto the backsplash.  Perhaps the intent was to help illuminate the room as a whole by that reflected light.)  I used a total of 19 lights wired in series in two separate strings.  Each string has its own dimmable power supply and a small potentiometer to control its brightness.  Everything is mounted under the cabinets, as shown at left.  The power supply is screwed in place using mounting tabs on its case, while the potentiometer was just hot-glued in place.  The solderless connectors on the LEDs made stringing wires between the lights much easier; no need to use the soldering iron in the kitchen!  It can also be seen in the photo at left that the existing light fixture (top-right corner of the photo) is being used as a junction box for wiring to the power supply.  The plan, eventually, is to take out the old light fixtures entirely and house the power supplies and dimmer potentiometers in a nice small enclosure.  But for now, the old lights do a good job of covering up the holes cut in the wall and back of each cabinet for the wires.  All of these components are hidden when looking at the cabinets from standing or sitting height.

Below are before and after photos showing the kitchen with the original under-cabinet lights and the LED lights.  It can easily be seen how the original lights lit the countertops unevenly, for example the counter to the right of the sink is well-lit only on its right half because that is where the only light in that section was installed.  The counter at far left was dark because the lights had to be left off due to the heat they generated.  In the second photo, the LEDs light all of the counters uniformly.  The lights were spaced between thirteen and fourteen inches apart, and this proved sufficient to provide even lighting.  Although it isn't obvious in the photos, the original fixtures provided very yellow light.  The LEDs are whiter in comparison.  Even though I chose the 'warm white' LEDs, they don't have any obvious yellowish tinge.  These look just right, but I think the neutral or cool white ones would have appeared bluish or overly harsh.

Some final thoughts:

• We were a bit concerned that the bare LEDs would cause glare, reflecting into the eyes of anyone working at the counter.  That is one reason I initially looked at putting the LEDs in the existing fixtures, to use the frosted glass of the fixture to diffuse the LED's light.  Once we tried mounting the bare LEDs, it turned out to not be a problem at all.
• With the dimmers adjusted to match the light output of the original light fixtures, the whole system draws less than ~25 W -- less than 10 % of the power draw of the original lights!
• LEDs generally don't burn out, they just slowly get dimmer over time (usually measured in tens of thousands of operating hours, but it depends on the operating temperature of the LED).  Since these LEDs and power supplies aren't being pushed to their rated power, there is lots of room to turn up the current as the LEDs get dimmer over the years.  With their relatively cool temperature now, they should last the life of the house!
• One can get strips of LEDs for this purpose that can be cut to length and come adhesive-backed for easy installation.  They are cheaper as well, since they don't need heat sinks.  I rejected using them here because I overestimated the light output of the original fixtures by about a factor of two.  I expected to have to run the LEDs at at least 550 mA, for ~ 150 lumens per LED or ~ 500 lumens per meter.  (And so I got 700 mA power supplies and sized the heat sinks accordingly!)  In the end, the LEDs are usually run at 250 - 300 mA of current, so I could have used a strip such as this one and saved some effort and money.  The strips aren't quite as efficient because they use resistors to balance and help regulate the current in parallel strings of 3 LEDs each, but they are still much more efficient than incandescents!
• Despite the higher cost of my approach, I found that total cost of components for the LED lights was about the same as the (retail) price of the original light fixtures.  So the LED solution is not more expensive than incandescents; uses less than 10 % of the power of the incandescents; requires less maintenance (no burned-out bulbs); provides whiter, more even light; and does not cause any problems due to heat generation.  Win!