bugbear writes:

It's easier on the brain to just do a really long exposure;
a half-frame doesn't matter (much) if you're exposing 60 frames
anyway.

Yes, so 1/2 or 1 second exposure works really well.

Tripod and a 1Sec exposure works every time, and I don't need
to know the refresh rate.

The problem with 15 seconds is that you can get reciprocity failure
effects with film or hot pixels showing up with CCD sensors. Plus
digital cameras often take 30 seconds to shoot a 15-second exposure
because of dark frame subtraction (noise reduction), which is a long
time to wait.

If there's enough light for a 1 second exposure with reasonable aperture
and depth of field (and in my experience there's lots of light), why
use 15 seconds and acquire additional problems?

Dave