Incandescent Bulbs, and LEDs Only in Daylight

What I do

Most of the house is incandescent. The few LEDs left are daytime-only.

What I am actually optimizing for

Not efficiency. This is a choice that costs me on the power bill and I am making it anyway, because the variable I care about is what the light does to the hours before sleep.

Incandescent light is thermal — a continuous spectrum weighted heavily toward the red end, closer to firelight than to daylight. Most LED white light is produced by a blue emitter with a phosphor coating, which leaves a pronounced blue spike even in bulbs marketed as warm. Blue wavelengths in the evening are the ones that suppress melatonin and push sleep onset later, which is the entire mechanism I am trying not to trigger at 9 PM.

The other difference is flicker. LEDs driven by cheap drivers modulate at a rate that is invisible but measurable, and the reports of eye strain and headaches around it are common enough to take seriously even where the literature is thin. An incandescent filament has thermal mass — it physically cannot flicker at that rate.

Why daytime LEDs are fine

Because during the day the blue is not a problem, it is the point. Bright, blue-weighted light in the morning is the signal that anchors the whole rhythm. The same bulb is useful at 9 AM and counterproductive at 9 PM, so it is the timing being controlled rather than the technology being banned.