LED Lamps are "Easily Dimmable"

a guest post by Lisa J. Reed, Lighting Designer

LED Lamps are Easily Dimmable

Everyone is crazy excited about LED lamps these days, and one of the reasons is because they are “easily dimmed.” I have two questions about that phrase:

  1. What does “dimmed” mean?
    Just because the light output of a fixture can be reduced, that doesn’t mean it is really well dimmed. Pitfalls to watch for with LED dimming? Flicker, steppiness or uneven dimming, only dimming a little bit (so you can’t really see a dramatic difference), and deciding whether or not we want the light to become “warmer” as it gets dimmer.

    Some LED lights have an annoying, almost imperceptible flicker when they are at a low light level. Others just jump, flicker, or step while the light level is being reduced but then stabilize once you reach the desired level. This may not be a problem in certain applications but when the space is occupied during the dimming or when the dimming is done slowly, over several minutes (as in a restaurant between the lunch and dinner scene) this steppiness can be disconcerting. In other cases, the LED lights can only dim to 15 or 20 percent. When a light is dimmed to 15 percent, the human eye perceives it as about 40 percent of total light output – not low enough to create great ambiance!

    Again, in our restaurant example, we may want to take those lights to a much lower level. And finally, another hot question in the industry right now is this: when we dim the light level, do we want the color temperature of the source to get warmer? With incandescent, dimming naturally also warms the color of the light so that a very dim incandescent lamp has a soft orange glow. LED technology allows this only as an option. LED sources can either stay the same color as they dim or they can become more orange, but that is an option that must be identified and specified.
  2. What does “easily” mean?
    Just because an LED is dimmable, doesn’t mean that it will dim on any old dimmer switch. If you replace existing incandescent or even fluorescent fixtures but you leave the same old dimmer on the wall, it likely won’t work. What’s more, the dimmer that will work with one LED product might not be the best choice for a different LED product. Anytime you want to dim an LED, you will need to check its dimming compatibility.

    Does it require a 0-10V dimmer? Or does it need a forward or reverse phase-cut dimmer? What if you want to use it on a DMX system? Or how about DALI? All of these questions need to be asked and answered before you start dimming an LED. It is important to think about LEDs, their drivers, and their dimmers as a complete system, rather than separate parts. The individual parts may not be compatible with one another. It has to operate as a system.

So while LED is definitely dimmable, and more easily so than some other lighting technologies, it doesn’t mean we can dim it without thinking about it! Checking dimming compatibility is just one of the many new jobs for a person who wants to install LED lighting.

Lisa J Reed photo - Lighting Blog

Lisa J. Reed has been attracted to lighting (like a moth to a flame) for 20+ years. She is the Founding Principal at Envision Lighting Design, LLC in St. Louis, where she designs, teaches, and writes about architectural lighting.


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