According to FAR103, you have to operate ultralights between sunrise and sunset, or between the times laid out in the Air Almanac (if you're in Alaska.) This means that the FAA has determined that certain lighting requirements exist for ultralight pilots, but has laid them down in a time-defined manner, instead of a lighting-involved one. Under normal situations, this is fine - you don't get enough eclipses, volcanic eruptions, or alien invasion fleets blocking the sun to make rules based upon luminosity.
At the moment, there are a number of arguments breaking out about whether Ultralights can fly in my area. It's just after noon, but because of the fires in California, high-altitude smoke and clouds are bringing lighting conditions to being comparable to 30 minutes post-sunset.
If the sun is up and pilots stay clear of clouds (and smoke plumes), and - of course - we're not violating a TFR, is the assumption that we can fly without a 3-mile visible light, or is there something in the FAA regs that deal with this situation?
To reiterate - we're not flying anywhere near the fires, we're not flying in a TFR zone or other controlled airspace, and we're not flying within a mile of a cloud or smoke plume.