Bright Ideas

Frequently Asked Under Cabinet LED Lighting Questions

Posted by Geoff Walling on Apr 12, 2016 4:40 PM

LED Under Cabinet Lighting (UCA) is one of the most popular RAB Design products since it has a wide range of applications in residential, commercial and Industrial settings.  Our UCA product is typically used in kitchens, but also under shelves in industrial panels and even on boats. We get a lot of inquiries about how to install and customize our Under Cabinet Lighting; this post will focus on some of the most frequently asked questions.  


What are the limitations of a “run”?

The most common questions we get are around an LED “run.” By “run” we mean the maximum series or length of Under Cabinet LED strips before you get a voltage drop. One of the misconceptions people have is that you can only do a two metre run off one power supply. On the original RAB Design UCA product, the standard maximum length of run is about 32 watts in series, this is about 80” of fixtures when using UCA or , or 120” on the UC product.

These lengths are guidelines; always ask your electrician to ensure they account for voltage drops when using long runs of wire between fixtures.  Note there is still a volt drop if the wire is coiled up between fixtures,  always try to  use the correct length of wire - they are pre-packed as 2”, 6”, 40” or 80” - or you can use a DC cable conector with LVT or bell wire to get the exact length.

You can actually have two or three runs on one power supply if you add a splitter. To use an example, if you are installing Under Cabinet Lighting with a 96 watt power supply, you could do two runs of two metres (32 watts) each. In this case you would need to use a splitter off the hardwired kit and have two leads going to the product. Also, you can still use a motion sensor with the splitter.

What are the voltage requirements of the UC, UCA , UCP and UC series?

All fixtures use 24 volts DC as their input voltage, this can supplied by one of our plug in power supplies, dimmable or non-dimmable hardwire powers.  In industrial applications such as PLC or control panels, the 24V DC source can be supplied from other DC power supplies. In 12VDC automotive and boating applications, you will need to use a step up transformer to achieve 24VDC or you can special order 12V DC fixtures. 

What measurements should I keep in mind?

Another question we get a lot is how much space to allow for when doing your Under Cabinet Lighting set-up. The basic principle is to allocate an inch for each direct connector that you use and an inch and half for each power supply plug. If you are using a DC connector you will need to allocate two inches - for example, if you are using bell wire (18 gauge wire) to run to a basement. If your set-up includes a dimmer, you will need to allocate an extra inch and two inches for a motion sensor. 

What should I consider with colour temperature?

Colour temperature is one of the trickier aspects of lighting since it’s more about aesthetics, but also requires some knowledge of lighting principles to get it right. When selecting a UCA you need to think about the colour temperature in terms of the desired effect you want in the room. This means accounting for the colours in the room.

For example, if the walls are white and you use a warm white UCA, it will look more yellow. If you want to keep the colour of your wall, then you would select a natural white UCA. If you have a brown tile for your counter top, warm white might be the best choice.  Standard LED Under Cabinet Lighting units are offered in 3000 kelvin (warm white) and 4000 kelvin (natural white).

Think of warmer colours being earth tones like brown, green and beige typically found in kitchens with natural wood cabinets and/or brown marble/stone counter tops.  These would typically be best suited for 3000k lights.

Kitchens with primary colours, stark white and stainless steel, tend to appear brighter when cooler colour 4000k lights are used.

What are my limitations with lighting controls? 

We also get a lot of questions around how to correctly install motion sensors and dimmers with Under Cabinet Lighting.  There are a wide range of applications for motion sensors with UCA fixtures, including university cubicles, kid’s desks, work benches, inside a cupboard, crawl space or panel box.

  • Will the motion sensor work if it is placed between two UCA strips? ? No, only the fixture after the sensor will be controlled by the sensor.
  • Can I use a wall dimmer with a plug in power supply? No, line voltage (wall) dimmers can only be used with dimmable hardwired power supplies. If you are using a plug in or non-dimmable power supply, you could use our patented touch dimmer to turn fixtures on/off and touch to dim up or down.

Why am I getting flickering?

Flickering often happens if you are using a line voltage dimmer, the line voltage dimmer might not recognize the load. Some electronic line voltage dimmers require a minimum 40 watt load.  For example, if you have a run with one 16W (40” section) this may be too small a load for the dimmer to control, and you may get flickering through the dimming cycle. Most of the older (and cheaper) magnetic/incandescent dimmers will work very well even at very small loads of 3 watts.  Some of the new electronic dimmers have trim adjustments that allow the installer to find flicker points in the dimming cycle and use the adjustment to remove or reduce flicker.  Please consult our customer service team if you are having trouble finding the right dimmer.

What’s the correct connection set-up?

If you need to create a long run (more than 80”) or if you need to fish wire behind dry wall,  you should use the DC connector with 18AWG  2 strand wire.  Typically known as 18-2 LVT(low voltage thermostat wire) or 18-2 Bell wire, always ensure the wire you use is properly certified for the application.

If you are using the DC connector, you need to make sure the negative and positive from the power supply, got to the negative and positive of the connector. If it’s reversed, the fixture will not light and you would need to undo the wire and reconnect it.

Learn more about Rab Design's Under Cabinet Lighting (UCA) series by clicking the button below. If you have any questions that aren't covered here, don't be shy,  we are happy to help.

LED Under Cabinet Lighting Detailed Guide

About the Author: Geoff Walling is a lighting specialist based in RAB Design's Toronto office, where he fields questions daily about lighting layouts, installation and fixture selection.

Topics: Under cabinet LED