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Posted By Topic: LEDs and dimmers

Nov 16 2014 14:17

Is there a reason besides minimum loading why I'm being told the LEDs I'm interested in call for a leading edge dimmer?

I have an existing PDL 624TM trailing edge dimmer, but the minimum loading for these is 20W and 10x 3W LEDs = 30W. Shouldn't this work?

On the other hand, the leading edge PDL 620K (now obsolete) has a minimum loading of 150W so that won't. I'll be buying new dimmers where needed, but I'll reuse the others where I can as they're not very old.

I also don't like the fact that leading edge dimmers can buzz.

Still keen to hear where people are buying their LEDs and what to look for - I want quality this time.

Nov 17 2014 15:39

I would not recommend a leading edge dimmer with an electronic transformer/driver. The driver will have filter capacitors on the input side and a leading edge dimmer will create very high current peaks.

The only reason I can think that a particular driver requires a leading edge dimmer, is that dimmable drivers actually work by "finding" the dimmers switching point (on the AC phase), and translating that to a current output for the LEDs.
So the driver has to be designed to find either a leading or a trailing edge switching point or be an even cleverer one that can detect which dimmer type is being used (these are usually labelled as a universal driver).

Nov 17 2014 16:07

Thanks ThatGuy; this is all pretty new to me.

This is what I'm looking to get, or something similar, to replace some lamps in some old candelabras:

They are straight replacements for 230V lamps so the drivers are incorporated into the bases. I emailed the retailer and he said they were compatible with leading edge or universal dimmers which surprised me.

Hmmm - perhaps I should keep looking? I bought a 624TM not so long ago for incandescent, thinking it would be compatible if I upgraded to LED.

Also, all the PDL dimmers seem to have a 20W minimum loading - not so useful for smaller rooms. Are LEDs susceptible to amber drift on dimming in the same way that incandescent is?


Nov 17 2014 16:59

hmm, I'm not sure about those type of lights, I was talking about - say a typical downlight with an external constant current driver. I've seen photos of that kind of lamp, with just a capacitor and a resistor to limit the current, rather than a full electronic driver. I would go with what the supplier recommends.

I have not noticed any colour shift in the LED lights I have when dimmed.

Nov 17 2014 17:04

Thanks! Great to know that the colour has stayed the same for you - it's the one thing that frustrates me about dimming incandescents.

Aug 27 2017 22:07

[quote]Also, all the PDL dimmers seem to have a 20W minimum loading - not so useful for smaller rooms.[/quote]

How are others getting around this problem?

Aug 28 2017 07:13

The new PDL 624T have a minimum loading of 1 Watt.

Aug 28 2017 18:16

How new are they? The PDL website shows 20W minimum still, maybe their website hasn't been updated recently?

Aug 29 2017 07:10

I picked some up yesterday and they had the sticker "Improved for LED" on the bag, but still had the old datasheet in the bag showing min 20W. New data sheet can be downloaded from the link. Not sure why they haven't included the new datasheet with the dimmers suitable for LED yet.

Aug 29 2017 17:51

Thanks for that chau!!