Neither ViparSpectra nor AC Infinity claimed compatibility for the XS1500 Pro. AC Infinity's web site only says the KS5000 is compatible. It doesn't mention the XS1500 Pro, and that's why I asked about it. I didn't ask ViparSpectra about the KS5000 or any of their other lights.
Here's what AC Infinity has to say about dimming protocols:
The XS1500 Pro uses the PWM protocol, so in that way it is compatible. It doesn't go all the way to zero volts, however, so in that way it is not compatible. The light's lowest setting is 5%. That's why the controller can't turn the light off. The light is the problem, not the controller.
I use ViparSpectra XS2000 lights and I like them. I don't like how the dimmer operation was changed for the XS1500 Pro. Its knob only has 5 stops: 5, 25, 50, 75 & 100 percent. I want more control than that. It also seems silly not to be able to turn the light off with a switch.
ViparSpectra is apparently aware of the issue. Their customer support informed me of the problem (near the bottom of their reply).
Here's a screenshot of their reply:
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