Being stuck before computer display until very late in the night tends to feel much worse than same amount of hours during the day. If it's not gradual and you just turn computer on in the night - it feels like display hits you in the eyes.
f.lux is a software that adjusts color temperature for display to be easier on your eyes and brain at night.
What it does
In a nutshell app switches display to “cool” colors during the day (which is usual state for displays) and “warm” colors during the night. This makes screen easier to look at during dark hours and less likely to disrupt going to sleep afterwards.
While it is very hard to untangle subjective from objective for such kind of a functionality, it definitely reduces that hit-in-the-eyes effect. Since the actual brightness does not change the difference in how it looks is very clear and substantial. I have warm lighting in my room and displays suddenly started to feel like they belong at night, rather being pools of alien bright light.
App derives dark time from sunrise/sunset, which requires you to set latitude and longitude for where you are in the world. Web site has helper page to determine that.
Color temperatures for day and night can be adjusted (or even flipped) from defaults in settings.
While effect is very pronounced in a good way, it has as pronounced bad impact on colors. Unlike typical minor brightness/contrast adjustments it impacts colors much more and very visibly affects viewing angles - image can get outright orange.
It is hard to adjust to psychologically and totally unfit for color-sensitive work (for which there is option to disable adjustment for a hour). Luckily being stuck in browser or text editor of some kind is hardly color sensitive, but still takes time to get used to it.
By default transition between modes is unpleasantly rapid, but can be adjusted in setting to be dragged out for an hour. FAQ justifies default option as easier on resources so long change might be unfit for slower computers.
Your mileage may wary, but as for me f.lux makes very real and pleasant difference to working with computer at night.