General > General Technical Chat
LED lighting and planned obsolescence, intentional or not.
tom66:
--- Quote from: gnuarm on August 08, 2023, 05:18:28 am ---
--- Quote from: NiHaoMike on August 08, 2023, 05:00:36 am ---Wouldn't the easy way be to just buy dimmable LEDs which are much brighter than you need and just don't use them at full power?
--- End quote ---
1) There's no such thing as dimmable LEDs, just like CFLs. The controllers chop the AC waveform which doesn't work very well with these devices, even when they claim to be compatible, even when you combine specific model numbers that are claimed to be compatible.
2) LED brightness is controlled by current, not voltage. There's simply no practical way to make this work well, that doesn't burn excess power.
--- End quote ---
What? The majority of dimmable LED bulbs just follow the chopped mains voltage with a constant current LED driver. So the LED gets the chopped AC input, full-wave rectified to DC. This means they're a lot more sensitive to variations in mains voltage, unlike a filament bulb there's no inertia to speak of, so I haven't the greatest opinion of them. But they are dimmable, and they don't burn excess power when dim.
gnuarm:
--- Quote from: Marco on August 08, 2023, 06:53:36 am ---
--- Quote from: gnuarm on August 08, 2023, 05:18:28 am ---1) There's no such thing as dimmable LEDs, just like CFLs. The controllers chop the AC waveform which doesn't work very well with these devices, even when they claim to be compatible, even when you combine specific model numbers that are claimed to be compatible.
--- End quote ---
You can always buck boost. Also you can just say the lamp only works with trailing edge dimmers with adjustment pot and turn off at 90 degrees and let the customer figure it out. Full voltage always available after the rectifier, problem solved.
--- End quote ---
You really don't know anything about these devices, do you?
Marco:
They just convert conduction angle to PWM, it works fine. The only problem with LED dimming is that you don't have full voltage to work with after the rectifier with less than 90 degree conduction angle, which is a pain for the switching regulator. With extreme cost cutting some of the lower end manufacturers cut corners. Even then, with a modern trailing edge dimmer you can adjust minimum conduction angle, so if the bulb starts flickering just don't let it dim that far back.
If it absolutely has to work with any old dimmer in the wall and you absolutely want the same dimming range with the same range of the knob and otherwise say dimming doesn't work, then dimming doesn't work.
PS. The power supply for a trailing edge dimmer itself isn't entirely trivial either with two wires, needs to bootstrap somehow, meh it works well enough.
gnuarm:
--- Quote from: Marco on August 08, 2023, 11:13:27 am ---They just convert conduction angle to PWM, it works fine.
--- End quote ---
Except that they don't "works fine".
--- Quote ---The only problem with LED dimming is...
--- End quote ---
So you do know that it doesn't "works fine"!
I bought LED ceiling fixtures (with the LEDs inside) and the dimmer specified on the box. They have issues working together. It was hard, but I finally was able to reach the manufactures. Each one told me to return them. They had no solution to the problem. They didn't care that they didn't work. Their solution was simply to return the junk where I bought them.
That's not "works fine".
Kjelt:
Indeed ac dimming is and has always been a PITA for led lighting.
The good dimming drivers use DALI , 0-10V or nowadays wireless communication as Zigbee and BT as dimming input.
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