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> LEDs are inherently dimmable. What? This isn't true. LEDs function using DC current, and are either on or off. "Dimmable" LEDs have chips in the bulbs that u

> LEDs are inherently dimmable. What? This isn't true. LEDs function using DC current, and are either on or off. "Dimmable" LEDs have chips in the bulbs that use pulse-width modulation (PWM) to turn the diodes on/off at a different rate to create the dimming effect. All incandescent bulbs are dimmable (on AC power) with no additional hardware other than the dimmer, which adjusts the input voltage to the bulb. Try to do this with a non-dimmable LED and you'll damage the bulb.

sourthyme 3y ago
Does it damage the bulb? I thought it just pulsed at a visible rate because it can't turn on consistently. Does rapidly turning off/on diodes reduce the life of a bulb?
gizmo686 3y ago
I've never done it with lightbulb level LEDs, but with circut type leds, I've gotten them dimmer by simply using an oversized resistor. Modern incandescent dimmers don't change the voltage. They just chop off portions of the AC wave, which produces something like a PWM wave, except the on voltage is not constant. I wouldn't want to try using this chopped up wave to power anything more complicated than a light bulb, but I don't see how it would damage an LED.
housemusicfan 3y ago
> which adjusts the input voltage to the bulb This isn't exactly true; no one has used a rheostat for dimming in like 50 years since that just wastes power. Most incandescent dimmers implement cycle chopping where they clip the beginning or end of the AC cycle (the type used depends on the implementation). Most commonly done using a diac or triac. Most "LED" in wall dimmers work this way too because you can't PWM dim on the other side of the power supply. This is also why in practice most LED bulbs are shit and even the best bulbs will visibly flicker whilst dimming. Yes LEDs are DC but as a compromise you have to implement dimming on the AC side because homes are wired with AC power.
- midoridensha 3y ago
  >Yes LEDs are DC but as a compromise you have to implement dimming on the AC side because homes are wired with AC power. This isn't universally true. Here in Japan, there's commonly-available LED ceiling fixtures (that look something like UFOs) that are dimmable with a remote control. They surely use PWM dimming, but it's done in the LED driver circuit; the fixture is getting the same 100VAC at all times. They also commonly have bluer and yellower LEDs, so you can adjust the light spectrum with your remote control.
  - housemusicfan 3y ago
    Yes but we are talking about bulbs (with Edison base) here not all-in-one fixtures. Yes, the same could be said about ceiling fans with built in remote receiver. The problem with these of course is you need the remote, and if you lose it you're out of luck. Some manufacturers make a little dock for the remote that would go in place of the light switch but I happen to think those are silly.
    - midoridensha 3y ago
      >Yes but we are talking about bulbs (with Edison base) here not all-in-one fixtures. Sure, but there's little difference between the two practically. Both of them are a light-emitting device, which plugs into a simple, standard socket on the ceiling. The ones I refer to are bigger, since they're meant to light up a whole room, but otherwise not really different, except that the standard socket is a lot better and easier to use (you just turn the fixture a quarter-turn to plug it in).
cwillu 3y ago
You absolutely can dim an LED via constant current control. Nobody does it that way at scale, but the LEDs work that way just fine. Source: I have a 5-way constant-current dimmer on a breadboard on my desk driving 5 CREE XLamp CXA Series LED's.
- wlesieutre 3y ago
  Nobody does it that way in screw-base retrofit bulbs, but there's a whole world of commercial lighting where constant current is pretty widely used. Drivers from vendors such as Tridonic https://www.tridonic.com/en/int/product-finder/led-drivers?filterParams=category%3DPC_LED_DRIVERS%26OPERATING_MODE%3DConstant%2Bcurrent https://www.tridonic.com/en/int/product-finder/led-drivers?f... Advantages include lack of flicker and more reliable LED boards (hardly any components except for the LEDs). Drivers still fail, but it's nice to have them be a replaceable part.

sourthyme 3y ago

Does it damage the bulb? I thought it just pulsed at a visible rate because it can't turn on consistently. Does rapidly turning off/on diodes reduce the life of a bulb?

gizmo686 3y ago

I've never done it with lightbulb level LEDs, but with circut type leds, I've gotten them dimmer by simply using an oversized resistor. Modern incandescent dimmers don't change the voltage. They just chop off portions of the AC wave, which produces something like a PWM wave, except the on voltage is not constant. I wouldn't want to try using this chopped up wave to power anything more complicated than a light bulb, but I don't see how it would damage an LED.

housemusicfan 3y ago

> which adjusts the input voltage to the bulb This isn't exactly true; no one has used a rheostat for dimming in like 50 years since that just wastes power. Most incandescent dimmers implement cycle chopping where they clip the beginning or end of the AC cycle (the type used depends on the implementation). Most commonly done using a diac or triac. Most "LED" in wall dimmers work this way too because you can't PWM dim on the other side of the power supply. This is also why in practice most LED bulbs are shit and even the best bulbs will visibly flicker whilst dimming. Yes LEDs are DC but as a compromise you have to implement dimming on the AC side because homes are wired with AC power.

midoridensha 3y ago
>Yes LEDs are DC but as a compromise you have to implement dimming on the AC side because homes are wired with AC power. This isn't universally true. Here in Japan, there's commonly-available LED ceiling fixtures (that look something like UFOs) that are dimmable with a remote control. They surely use PWM dimming, but it's done in the LED driver circuit; the fixture is getting the same 100VAC at all times. They also commonly have bluer and yellower LEDs, so you can adjust the light spectrum with your remote control.
- housemusicfan 3y ago
  Yes but we are talking about bulbs (with Edison base) here not all-in-one fixtures. Yes, the same could be said about ceiling fans with built in remote receiver. The problem with these of course is you need the remote, and if you lose it you're out of luck. Some manufacturers make a little dock for the remote that would go in place of the light switch but I happen to think those are silly.
  - midoridensha 3y ago
    >Yes but we are talking about bulbs (with Edison base) here not all-in-one fixtures. Sure, but there's little difference between the two practically. Both of them are a light-emitting device, which plugs into a simple, standard socket on the ceiling. The ones I refer to are bigger, since they're meant to light up a whole room, but otherwise not really different, except that the standard socket is a lot better and easier to use (you just turn the fixture a quarter-turn to plug it in).

cwillu 3y ago

You absolutely can dim an LED via constant current control. Nobody does it that way at scale, but the LEDs work that way just fine. Source: I have a 5-way constant-current dimmer on a breadboard on my desk driving 5 CREE XLamp CXA Series LED's.

wlesieutre 3y ago
Nobody does it that way in screw-base retrofit bulbs, but there's a whole world of commercial lighting where constant current is pretty widely used. Drivers from vendors such as Tridonic https://www.tridonic.com/en/int/product-finder/led-drivers?filterParams=category%3DPC_LED_DRIVERS%26OPERATING_MODE%3DConstant%2Bcurrent https://www.tridonic.com/en/int/product-finder/led-drivers?f... Advantages include lack of flicker and more reliable LED boards (hardly any components except for the LEDs). Drivers still fail, but it's nice to have them be a replaceable part.