Dimmable LED bulbs & dimmer switches

[WimWalther]

Can dimmable LED bulbs ("dleds") be controlled from a regular, old TRIAC / SCR-based dimmer switch? The marketing literature seems to say NO, but why might that be? What might be the difference between standard dimmers and the new types specified for dled & cf bulbs?

Does running a dled bulb at lower brightness also extend its lifetime as we see with incandescents? If no, why not?

I'm sure more questions will arise.

 

[Chuck(G)]

The short answer, in my experience is--yes, but. You can dim the LED lamps, but the range is small and there's quite a bit of hysteresis in the result. That is, going from low dimmer setting to high, there's nothing, then the lamp comes on at about 2/3 brightness. You can then dim it down considerably. For the past 4 years, I've had a number of dimmable LED lamps on old-style triac dimmers and life doesn't appear to be affected.

I'm sure that an LED-specific dimmer has a smoother action and wider range, but I'm not convinced of the cost-benefit tradeoff. I can only speak from my own experience.

Now, dimmable CFLs were a disaster, but then so were CFLs in general.

 

[vwestlife]

Philips has dimmable LEDs that match the incandescent bulb effect of the color temperature getting warmer as you dim it, but they're hard to find in stores anymore because everyone is going crazy for RGB LEDs these days instead:

 

[WimWalther]

In my case, I'm using 5x GE 3.5/4W (40W equivalent) soft white decor bulbs with a basic $8 GE LED / CFL / incandescent rotary dimmer switch. Range of adjustment is wide with no obvious hysteresis effect. Compared to the old 40W incandescent bulbs, the color is almost identical - but whereas the old bulbs would dim to fully dark, the new LEDs still produce some low output when dimmed fully down.

Overall very happy with the change, it was the last light in the house that wasn't running CFL or LED. I still have a small stock of CFL which I'll likely use until they die off. Some of the CFLs in service have lasted 10 yrs, and they were the uber-cheap 8-pack for $6.99 units - though I think that was a subsidized price.

 

[WimWalther]

Wait.. people are crazy for RGB LED bulbs for what? For room lighting? You mean the Bluetooth type where you can dial up any color?

 

[Chuck(G)]

On a somewhat related subject, I still have a few of the night lights that take 120v E12 (candelabra) base lamps. These contain a CdS photocell and a triac and are pretty simple. When I try to use these with a 120V LED lamp, it doesn't work. The LED stays off. On a hunch, I opened one up and soldered a 220K resistor across the lamp contacts. Bingo! (Yes, I know that a new unit would be less trouble and less expensive, but I like to keep old stuff going.) I wonder if a high-value resistor across the lamp in a standard setup might make dimmer action a bit smoother. Just a thought.

 

[NeXT]

On a somewhat related subject, I still have a few of the night lights that take 120v E12 (candelabra) base lamps. These contain a CdS photocell and a triac and are pretty simple. When I try to use these with a 120V LED lamp, it doesn't work. The LED stays off. On a hunch, I opened one up and soldered a 220K resistor across the lamp contacts. Bingo! (Yes, I know that a new unit would be less trouble and less expensive, but I like to keep old stuff going.) I wonder if a high-value resistor across the lamp in a standard setup might make dimmer action a bit smoother. Just a thought.

I've heard of this being done with X10 lamp modules and switches. The triac circuit expects to see a resistive load but LED's don't deliver, so you get very erratic results until you put a resistor across the load.