Dimming LED lamps with ordinary dimmers.


Using a traditional phase angle control wall-plate dimmer (the usual type) is just a terrible way to dim LED lamps. The rough chopping of a 50/60Hz sinewave with sharp voltage transitions is very hard to convert to a proper smooth and flicker free dimming of an LED lamp over a decent range. LED lamps also provide a very low load with sudden drop-off of current which can make ordinary dimmers very unstable.

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  1. You are exactly right. The dimmer (as opposed to "dimmable circuitry") should be in the bulb or fixture, and receive commands via the power line. One simple command protocol is Blink'n'Dim. A short power interruption triggers gradual dimming or brightening, and another halts it. Technology to achieve this is described on ResponsivLED.com. As of this writing, no fixture manufacturer has embraced it. However, a 0-10V Blink'n'Dim Adapter is available on Amazon for fixtures that include 0-10V dimming capability.

  2. I think the easiest for the manufacturers is to have a remote that directly talks to the bulb, then the bulb could PWM its LEDs.

  3. Thanks again Clive for your, er, illuminating explanation of dimmables! I just revisited this, because I am coming up to a makeover in my flat in south east London.
    I have a couple of ideas I want to throw into the pot, and I may try them out if I can get hold of the necessary kit.
    1/ What if bar LED units were used instead? The principle involved would be to coil maybe 50 or 100 LEDs in a spiral fitting inside a lamp housing. The signaller (=dimmer) would then be in the wall switch, and I presume the PSU (driver) would, too – some reworking of cables needed. Instead of trying to lower the light output of a lamp's LED array, you'd simply reduce the number of LEDs lit. There are kits around that could be used, and a selection of bar LEDs, although I have not seen them in spirals. This could be worked round, however, by cramming modules and crafty soldering. But, their light output might be an issue. Ribbon lighting a possibility.
    2/ Another approach would be a bodge IMHO. I was considering say a dozen or more LED downlighters in my living room, but with two or three on a separate circuit. How to do that? Use half-wave rectifiers! All I would need is a double switch. The two or three downlighters could also be underdriven – my crude way would simply be to add resistors, just enough current to trigger them. This approach is simply to have a lot less total light coming out of the ceiling, rather than each individual lamp glowing feebly. Not as sexy, but all I need is not to fall over the coffee table!
    As a complication I would need to override the dimmed lights, but I think some extra circuitry would work, the simplest by using a relay. Maybe your fairground experience can point me in the right direction! Or you could do an update video…

  4. I think it would be a good idea to simplify the LED fixtures to be just a string of LEDs and a current limiting resistor. Then the dimmer would rectify and supply the variable voltage DC to the fixtures. Lower voltage = dimmed.

    When the fluorescent fixtures were too bright, they made a dimmer for each tube. It consisted of one plastic cylinder inside of the other. Each was printed with black stripes. When the cylinders were rotated so both stripes aligned, the tube was half dimmed. When the stripes were rotated to cover most of the tube, the light was very dim.

  5. Here's a better way: The driver chip should use a small portion of the AC in to heat a resistor, and set the LED brightness proportional to the temperature of that resistor. If the resistor heats like a tungsten filament, then so will the LED brightness, without any complicated circuitry. With a small, high value resistor this does not need to use much power.

  6. I have a "light" problem and if anyone is going to know the answer it's you, I have just installed 10 dimmable LED spotlights in my bathroom on a separate circuit to my main light and have changed my main light to a dimmable LED light (with remote) now my spots are working perfectly as I bought a double dimmer that is both Leading edge and trailing edge and has 3 programmable modes but my main light just flashes like crazy, I put the main light on just a normal single-pole switch and that works perfectly, so my question is can a dimmable switch work with a dimmable LED light that uses a remote for it's dimming functionality it's a Varilght V-PRO double dimmer if that helps, TIA

  7. you know there are dimmable led bulbs, i just wonder personally, do they work properly with a non-synced pwm dimming circuit (constant pulsewidth modulation)?
    i'm planning to make a digital dimmer myself, arduino nano, optocoupler, dual output transformer (+ – + to have a "separate" supply for the mosfet and arduino) and 3 fullbridge rectifiers (or 2 if i opt for an SSR, basically a TRIAC with an optocoupler)

  8. I have a 5 socket hanging light, in which I tried to install 5 decorative LED bulbs. The dimmer is about 20 years old. With all 5 sockets occupied by LEDs, performance was weird and erratic. If I put a standard incandescent bulb in one of the sockets, the dimmer works very smoothly.

  9. I have a 30 year old dimmer running 3x4w led. It works fine, very slight flicker at the very lowest brightness but the issue I have is its a rotary dimmer, the led is off at around 50% turn, it still covers full brightness range and doesn't cut off, its very dim before turning off. But its sensitive and moves quickly between brightness levels so have to turn it very lightly. With old bulbs when dimmer rotated fully off, there was still a small bit of light. How to fix this so that the led turns off when dimmer is fully rotated off.

  10. I’ve had good luck dimming the really cheap Chinese LED lights; the ones that have the plastic mat finish half dome, with a variable transformer. However not so with the more expensive glass LED lights that mimic filaments with the suspended yellow bars of LEDs.

  11. I work for a company that does LED lights, and when the customer wants dimmable lights, a variable resistor after the driver.

  12. One word: Variac

    Edit: Or remove the ac circuit, make them DC and add a diode to your dimmer circuit's output?


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