There are other ways to dim LEDs. Voltage stepping to control how much current can actually flow through the diode is one method (and this is how we test LEDs where I work, a 3V LED gets tested at ~2.4-2.6V. It will barely draw a couple milliamps despite the power supply set to allow an amp of draw.) The LED will light up, enough to see that it is working well, but not eye-searingly bright.
Voltage control of LEDs is extremely unreliable. The amount of current consumed at a specific voltage will vary wildly depending on temperature, process, etc. Nobody does voltage control for LEDs unless you do not care about consistent brightness at all.
> No, no it isn't. We can keep units within half a percent of starting output all day long.
On what, exactly? How can you possibly guarantee output using purely voltage control of an LED? LEDs (and laser diodes) are fundamentally current controlled devices. You need current feedback to set the output brightness operating points.
> Voltage control is done explicitly on laser diodes, to boot. And those are WAY MORE FINICKY than an LED.
Maybe if you don't care about the output power of the laser diode. Just not practical, and will change output power at the same voltage as temperature changes.
"How can you possibly guarantee output using purely voltage control of an LED?"
They don't tend to emit much heat when underdriven using voltage control because they can't pass high amounts of current at low voltage. Run an LED from 2.4-2.7V in discrete hundredths of a volt steps. You can get almost nothing to getting close to drawing 50mA doing discrete steps like this. This is how we also characterize and bin LEDs. As long as the LED is on a thermal mass, it isn't going anywhere near thermal runaway.
> They don't tend to emit much heat when underdriven using voltage control because they can't pass high amounts of current at low voltage.
No LED used for lighting in households is operated this way. You run them hot, because they can take it and you aren't wasting costly LED die area.
> Run an LED from 2.4-2.7V in discrete hundredths of a volt steps. You can get almost nothing to getting close to drawing 50mA doing discrete steps like this. This is how we also characterize and bin LEDs.
Discrete hundredths of volt steps? Maybe for characterization you can do this, but you expect residential LED bulbs to use circuitry able to precisely output in 1mV steps? Not happening.
I'll concede the point you can likely do characterization of LEDs using voltage control, but when you get to actually wanting to drive them for real usage in a lighting environment (i.e., not for some indicating function), voltage control isn't going to be useful. You don't have that precision, you don't have that thermal mass, and you certainly don't have the ability to drive them that weakly.
"No LED used for lighting in households is operated this way. You run them hot, because they can take it and you aren't wasting costly LED die area."
I literally work in this field, manufacturing thousands of LED boards of all types every single day.
Yes, they absolutely do. Especially under-cabinet lighting - it's deliberately underdriven via voltage because the thin strips of aluminum are basically a backing support strip and nothing more.
Let's grab what under my cabinets, for example. 4 LEDs in series. Okay, assuming 3V that's a 12V chain - the included wall-wart power supply is a 10.5V output supply at 200mA.
> Yes, they absolutely do. Especially under-cabinet lighting - it's deliberately underdriven via voltage because the thin strips of aluminum are basically a backing support strip and nothing more.
Under cabinet lighting and more generic cosmetic lighting tends to use constant voltage for the input supply, but is regulating its current elsewhere, within the cabinet module or LED itself. This is literally how the most common example of RGB LED strips (WS2812s) work. They have current limiting circuitry within the LED module itself. Getting the most brightness isn’t the most important thing, unlike in actual bulbs.
> Let's grab what under my cabinets, for example. 4 LEDs in series. Okay, assuming 3V that's a 12V chain - the included wall-wart power supply is a 10.5V output supply at 200mA.
Nobody is driving a standard white LED at 2.6V for lighting. Please, show me a datasheet of a white LED that has a reasonable lumen output at 2.6V forward voltage drop. That also doesn’t include any voltage drop allowance in any wiring, boards, or any circuitry, which can be significant in low voltage applications. Especially when cabinet lights tend to be daisy chained together. I’d guess your cabinet lighting is actually driving a string of 3 white LEDs in series.
