[marcosdumay]

That's a valid reason too. In an industrial environment full of rotating machines, thinking something is stationary because it's on the grid's natural frequency can be lethal.

It's way less of a problem with modern machinery, and leds will blink in uncorrelated phases in a frequency that is different from the grid's anyway.

[wtallis]

For residential lighting running off a single-phase supply, there are some annoying LED bulbs with simple half-wave rectification that strobe at the grid frequency with less than a 50% duty cycle (often seen with bulbs emulating vintage exposed-filament bulbs with no frosted glass). It would be interesting to see how much less annoying that kind of flicker is when you have a three-phase supply to a light fixture, so that at least one set of LEDs was illuminated at all times.

[quickthrowman]

There are no light fixtures that use three-phase power. At least that’s my belief, as I’ve never heard of one or seen one and I’ve been working in the electrical industry for almost a decade. You could theoretically arrange three lampholders like a delta or wye transformer [0] and connect a phase to each one and all three lamps will be lit, but the lampholders will be energized, so make sure to wear voltage-rated gloves when changing out the lamps ;) This is how three-phase resistive heaters are wired, the drop in ampacity and large resistive heating loads make it worth using three phase since ampacity is 1.73 times lower than it would be on a three-phase circuit than it would be at the same voltage as a single-phase circuit.

In the US, there are 208V single-phase and 480V single-phase lights that use two of the three phases. In practice, indoor lighting is either 277V (line to neutral on a 480V service) or 120V (line to neutral on a 208V service). Most commercial LED fixtures can use any voltage between 120V to 277V single-phase.

480V single phase is used for some pole lighting with long runs of conductors to handle voltage drop. Anything over 277V has to be elevated at least 22 feet off the ground per the NEC.

[0] https://en.wikipedia.org/wiki/Delta–wye_transformer