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Are dimmable LED lamps as mythical as unicorns?

Are dimmable LED lamps as mythical as unicorns?

If Amy Poehler and Seth Meyers ever reunite to perform Saturday Night Live’s Weekend Update sketch, “Really!?! With Seth & Amy”, I think several frustrated LED lighting consumers might offer up “dimmable LED lamps” as a viable topic. Because, really. LED are dimmable? Do flicker and load-balance issues indicate a successful dim? Really!?!

Dimmable LED lamps

 

 

 

 

 

 

 

 

The typical story: You purchase an LED lamp that features dimming, but once installed and dimmed, you notice a slight flicker. “That can’t be right”, you say. You remove the flickering LED and install another one. Crossing your fingers you slide the dimmer switch. “Huh, that flickers too”. You pick up the box to double-check that the lamp is dimmable. Check. In desperation, you try installing both lamps in the track. The flickering stops. You add a third lamp to the track. The flickering starts again. “What is going on here?”

Dimmable LED lamps are struggling to, well, dim, because many dimmer controls on the market are designed for incandescent lamps—which use a different technology to dim. Depending on the age of the dimmer, you may have an older, simple, resistive dimmer or a more modern “phase-cut”. The line voltage in our homes varies between plus and minus 120 Volts sixty times a second. Phase cut dimmers work by removing part of that voltage and reducing the supply to the lamp. For incandescent lamps these are called “forward phase” as they restrict the first half of the voltage.

forward phase current

 

 

 

source: http://www.lutron.com

 

LEDs, particularly low voltage LEDs, can also operate using a phase-cut dimmer, but they work by reducing the second half of the voltage – a “reverse phase” dimmer.

reverse phase current

 

 

 

source: http://www.lutron.com

 

LEDs are actually very simple devices to control. They operate by having a constant current supplied to them by a driver chip within the lamp and by varying the level of that constant current the light output can be smoothly adjusted. However, the LED dimmer needs to be compatible with the driver in the lamp. Standards exist for LED dimmers that specify certain control voltages that the dimmer transmits to the driver to adjust the current, but not all dimmers do this and not all lamps have drivers that are configured correctly.

Manufacturers are starting to offer dimmer compatibility specifications and their websites are often the best place to start, but it’s worth noting that the dimmer isn’t the only element involved. For low voltage circuits, the transformer also plays a large role. Various combinations can affect an LEDs ability to dim successfully—and each dimmer has a minimum and maximum number of a specific type of lamp that it can support. Just to illustrate the point, we have been able to create flicker with MR16 lamps from a range of suppliers (even “reputable” manufacturers) who claim near perfect dimmer compatibility. We are also able to dim “non-dimmable” lamps quite successfully, so we can certainly understand the level of confusion that exists.

So, what steps can you take to ensure you’re not left with a non-dimming, dimmable LED lamp? The first people to ask are of course the lamp, dimmer, and fixture manufacturers.

  1. Discover the compatible dimmers for your selected lamp. You can either ask the lighting manufacturer/seller or obtain the lamp’s data sheet specifications.
  2. Ask the manufacturer/seller if your specific fixture will support the load of the lamp.
  3. Tell the manufacturer/seller if the intended use is with a low-voltage circuit and pass along any transformer information you can.
  4. Once you’ve accumulated all the data, you may want to purchase a few lamps for testing purposes. If the manufacturer/seller stands behind their product, they should have a decent refund policy should you need to return the lamp.

So while LED lamp dimming remains unpredictable based on numerous factors (and very specific combinations of all those factors), the future is not all bleak. Dimming capabilities are improving, and—more to the point—solid state lighting-compatible dimmers are becoming available. But if in doubt as to whether your LED lamp will dim, ask!  Most lamp manufacturers will be happy to test a specific dimmer with their lamps. We certainly are.

 

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Sarah Bailey

Sarah Bailey

Manager of Marketing at Leapfrog Lighting
Sarah Bailey is the Manager of Marketing at Leapfrog Lighting. She has an interest in all things SSL, the environment, and, being a Canadian, hockey. She is an active participant in several LED lighting groups on LinkedIn, where many of Leapfrog's blog posts are discussed.

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