I go for a kind of off-white yellowish parchment coloured background.

I'm partial to darker themes. Full black only when I'm in a console/terminal, and I typically have the text set to green. For everything else, a decently dark gray (somewhere around 0x40) with a much lighter text feels best.

Dark. Apparently it's bad for your eyes, but I feel like it's much more comfortable to read.

According to some research some time back reading books in the dark is not bad for your eyes, just more fatiguing.

I prefer light themes in a well lit environment, I also up my screen brightness to max. The increased light intensity helps constrict the pupils, resulting in sharper images, which in turn allows me to sit further away from the screen and not having to lean forward as much.

My color scheme is a slightly modified Solarized dark theme.

And I prefer well-lit environments.

It's all about reducing contrast against your ambient setting. I work in well lit environments with bias lighting, so a light, not quite white background and dark text works best. It's the opposite if you work in dark environments, though you should probably bias light regardless.

Working in bright environments on a dark theme is just uncomfortable for long stretches.

I'm also curious how many of you calibrate your screens and what brightness you run at. I generally work at 120 cd/m2.

It's all about reducing contrast against your ambient setting. I work in well lit environments with bias lighting, so a light, not quite white background and dark text works best. It's the opposite if you work in dark environments, though you should probably bias light regardless.

Working in bright environments on a dark theme is just uncomfortable for long stretches.

I'm also curious how many of you calibrate your screens and what brightness you run at. I generally work at 120 cd/m2.

Even though I work in various lighting environments (from a brightly lit office to a night club), I tend to operate a dark theme. I adjust the brightness levels as needed (screen has to be brighter in a brighter environment).

Dark. Apparently it's bad for your eyes, but I feel like it's much more comfortable to read.

I'd argue it's the exact opposite, less light means having it easier on your eyes (hence why it feels more comfortable). Just make sure that your text is actually light gray instead or white, because the eyes will perceive bright colors stronger than usual (on the flipside, this means that white becomes a suitable color for emphasis by providing more contrast).

I guess the biggest problem right now is that dark screens eat up more power on LCD screens =P (but for OLED screens it's the other way)