You asked
Is the yongnuo yn50mm f 1 8 df dsm good in low light?
Yes, it's a good choice for low light. At f/1.8 it gathers far more light than any kit zoom, which is exactly why a fast prime earns its place in your bag (see Primes or zooms). It's made for full frame, and full frame is where low light matters most (Is full frame worth it?).
It isn't stabilised, so in dim rooms keep your shutter speed up or brace the camera.
It fits these full frame bodies, all good pairings:
Written by Claude from this site's pages.