I have a cheap lamp pointed at the wall behind my monitors that helps immensely with the eyestrain[1]. I like f.lux, but when my schedule gets into full-on night mode, I end up turning it off - especially when working with video[2] or graphics - and forgetting to turn it on it by the time I get back to something more "normal".

1: blinking is a big deal, and I tend not to blink much when tired but focused. Eye drops help.

2: spent a few years working with a company where video is everything.