It's not a "necessity," it's a personal preference.
I started out programming on a dark theme (the emacs default) but I've used a light theme professionally for about 15 years (and no other dark applications). I prefer the light theme and I don't find it hard on my eyes one bit and I have astigmatism.
https://ux.stackexchange.com/questions/53264/dark-or-white-c...