This winter I installed a 16-circuit subpanel and rewired the second
floor. The sub is fed from the main via a 60A 250v circuit over 6/3.
Everything has been working fine ever since, but I haven't really been
pulling much on these circuits until this week.

Today I'm noticing that when one of my window A/C's compressor kicks
on it is flicking the lights. But these lights are on a different
circuit (same panel). I did not expect this. The A/C is pulling
about 10A (120v) on a 20A dedicated circuit. Other power being drawn
from this panel includes:

-computer: ~5A on a dedicated 20A circuit
-computer and extras: ~5A on a dedicated circuit
-another A/C: ~8A on a dedicated circuit
-lights: ~? (1A maybe) on another circuit

So total I doubt I'm drawing more than 30A of 120V, so I can't be
maxing out the feed, right? That feed should give me 96A of 120V (80%
of 60A at 240V).

So what's the deal? Why would any lights on a different circuit
flicker when the compressor kicks on on another circuit? To be fair,
the flicker is subtle. It's not huge, but it's there.

thanks