| Old-school dimmer switches were rheostats, and they got hot. Pretty much all dimmers now are TRIAC-based, which is a semiconductor that turns on partway through the AC wave, then turns off at the next zero-crossing, repeat. It chops the waveform so the light only gets power for a fraction of the time. An incandescent bulb works largely the same with either type. (You may hear the filament "sing" on a TRIAC dimmer since the fast-rising waveform edge has a lot of harmonic content, but this is usually very faint.) LED bulbs are non-dimmable by default. The typical job of a power supply is to ignore variations in the source and deliver uniform power to the load, and that's just what they do, driving the emitters at a constant brightness regardless of what the dimmer does, until it's letting through so little power that the poor thing just shuts off. Or flickers madly. Dimmable LED bulbs are actually super tricky, because the power supply has to measure the distortions in the incoming waveform, interpret that as a dimming command, and use that to control the output to the emitters. Any jitter in the measurement sampling means the resulting brightness will bounce around. Any jitter in the waveform, which an incandescent might've ignored as long as the area-under-the-curve was equal, might be picked up by the LED power supply and misinterpreted as a changing dimming level. It all sucks and we should abandon it immediately. LEDs should be driven with DC. But there's an awful lot of installed fixtures to keep us from that utopia. |
Every LED luminaire or lamp already has a DC inverter inside of it.
Also, you can get (158) 28w 2x4 LED fixtures on a single 277V 20A circuit with #12 wire, DC lighting branch is never going to happen. For reference, that will light about 12,000 square feet of space assuming 9’ AFF for ceiling height.