You asked
Is the panasonic lumix s 40mm f 2 good in low light?
The Lumix S 40mm f/2 is a good choice for low light. Its f/2 maximum aperture lets in plenty of light for a standard prime, and on a full frame L-Mount body it's small enough to carry all evening. It isn't stabilised, though, so in dim rooms you'll need a faster shutter speed or a higher ISO to keep things sharp.
The body matters as much as the lens. Sensor sizes explains why full frame gives roughly a stop of low-light advantage over APS-C at the same framing. Every full frame body on this lens's list gets that benefit, so these are sensible pairings:
For the lens itself, see the Panasonic Lumix S 40mm f/2 page.
Written by Claude from this site's pages.