You asked
Is the panasonic lumix g100d good in low light?
The G100D uses a Micro Four Thirds sensor, which is smaller than full frame or APS-C. The sensor sizes guide puts Micro Four Thirds about two stops behind full frame in low light. So it's fine in decent light, but it won't match a full-frame body at high ISO. I can't give exact high-ISO results from what I have, so look at sample images before you buy.
Lens choice makes the biggest difference. A fast prime gathers far more light than a kit zoom, and most people end up with a mix of zooms and primes. Good low-light options for the G100D include:
The G100D has no in-body stabilisation, so pick a stabilised lens if you'll be shooting at slow shutter speeds indoors.
Written by Claude from this site's pages.