The rules for always on displays for watchfaces for CIQ 5 and higher devices is no greater than 10% luminance. But I have been finding that on actual watches, it seems like the former no more than 10% of pixels on also still applies. Exceeding this will turn off the display after a few minutes, even if the luminance is well below 10%.
The Screen Burn-In Simulator Tool presently only displays total luminance for CIQ 5 and higher devices. It needs to also display % of pixels on so that developers can check their always on displays properly.
