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Trailing edge or leading edge LED dimming?

Trailing edge or leading edge LED dimming?

In our previous blog, Are Dimmable LED lamps as Mythical as Unicorns, we examined whether retrofit LEDs can successfully dim using lighting control technology designed for incandescent light bulbs. Due to the continued scrutiny surrounding LED lamp dimmability, today we’re examining another element of LED dimming: leading edge versus trailing edge dimming.

The rising cost of energy is certainly driving consumers, retailers, and commercial property owners alike to seek out energy-efficient lighting technology—the most efficient of which is LED. There is very little tolerance, however, for energy-efficient products that detract from the look and feel of the space. Dimming is one such lighting feature that can deliver that desired ambiance. Our retail customers are certainly unwilling to sacrifice store presentation to save on energy, as it ultimately affects their bottom line of sales!  We’re even starting to field more questions about the compatibility of our products with various dimmers and dimmer technology. Dimming is important!

This week, for example, we were asked whether our PAR lamps are compatible with trailing edge and leading edge dimmers. So let’s take a closer look at these two dimming technologies specifically for retrofit LEDs running off the Mains voltage.

Trailing edge dimmers (aka “electronic dimmers”):

  • The electrical current (sinusoidal signal) is turned off at the end of the AC input waveform immediately before the zero crossing
  • Traditionally used for electronic drivers or low voltage transformers (capacitive loads)
  • Is not subject to a high inrush of voltage that leads to a high inrush of current
  • Does not cause buzzing sound when dimmed

Figure 1: Trailing edge. Source: Shuttle Lighting

Leading edge dimmers (aka “triac dimmers” or “incandescent dimmers”):

  • The electrical current (sinusoidal signal) is turned off at the front of the AC input waveform immediately after the zero crossing
  • Traditionally used for incandescent lamps or magnetic low voltage transformers
  • Produces a quick inrush of voltage into the load every half cycle which leads to a high inrush current into the electronic components of the LED lamp
  • Causes buzzing sound when dimmed (though buzzing is not always perceptible and is dependent on many different factors, such as lamp design and number of lamps on a circuit. Even the dimmer itself, such as whether it allows dimming level adjustments and its minimum load requirements).

Figure 2: Leading edge. Source: Shuttle Lighting

Trailing edge dimmers are a better fit for LED lamps. However, because LED retrofit lamps are more likely to be installed on existing dimmers used for incandescent or halogen lamps, many manufacturers design and test their LED lamps to be compatible with leading edge dimmers. Leapfrog Lighting is no exception.

So the short answer as to whether our PAR lamps work with trailing edge or leading edge dimmers is that they work with both. However, we’ve gone through great lengths to test with many different dimmers and only claim compatibility with those tested dimmers, even though they’ve been found to work with quite a few others.

If you are concerned about dimmability of your LED lamp with your existing dimmers, always consult the manufacturer’s product datasheets or contact the manufacturer directly. They should be able to provide you with test reports indicating compatibility.

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5 Responses to Trailing edge or leading edge LED dimming?

  1. Hi, Sarah,
    I really appreciate this article on dimmers for LED’s. We have 80 Sylvania LED 8W bulbs in a restaurant and have tried 3 different leading edge dimmers. All caused intermittent flickering at minimum dim. All dimmers were also listed by sylvania as compatible.
    After reading your article I realized all of our test dimmers were lead edge so I will now try a trailing edge (electronic) dimmer. Tech Support with Lutron, Leviton, nor Sylvania were very helpful beyond telling me what I could read in their compatibility charts.

    • Hi Jeff,

      Thanks for your comment. I’m going to email you right now to put you in touch with our technical lead. He’s spent a lot of time investigating dimmers and LEDs and should be able to assist you further. – Sarah

  2. Could you help me with acquiring a 2000w or 2500w trailing edge dimmer,for a Restraunt with 24 x 58w Led 600mm x 1200mm panels,manufacturers recommend a trailing edge unit.Thanks Peter

    • Hi Peter, I suggest that you talk to your electrician in order to receive a recommendation, or ask the manufacturer of your LED panels to recommend a specific make and model of dimmer. There are many types of LED panels with different power requirements so your manufacturer will know better than anyone.


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