Do dark conditions due to high-altitude smoke prevent ultralights from flying? 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.
Thanks...
The only regulations that apply to ultralights are in part 103. Apart from the obvious visibility and cloud clearance (103.23) and daylight (103.11) ones I see two others that could apply:
103.9(a):

No person may operate any ultralight vehicle in a manner that creates
a hazard to other persons or property.

This seems to be the part 103 equivalent of 91.13 (careless and reckless operations) and it's also written broadly. If you do go flying and something goes wrong, the FAA might argue that flying in marginal conditions was creating a hazard to other pilots or - if you lost control of the aircraft - to people on the ground. Whether or not that's plausible would depend heavily on the specific situation, of course.
103.21:

No person may operate an ultralight vehicle except by visual reference
with the surface.

In low light conditions with a lot of cloud and smoke around, it could be difficult maintaining visual reference.
So, if you're flying at noon, maintaining the required flight visibility, maintaining visual reference with the surface, staying out of TFRs, and not doing anything dangerous, your flight is probably legal.
But the important question here is &quot;is it safe?&quot;, not &quot;is it legal?&quot;.