Most modern monitors (and operating systems for that matter) have functions for day and night colour temperature schemes. I use it a lot since I love reading in bed but don't want to give night blindness to my other half.
If the OS has it, you can set it to gradually phase in and out of the temperature change at a particular time. The Radeon drivers go one step further by understanding that as the year progresses, "night" and "day" happen at different times.
There is a solution, but it's a bit more complicated and requires introducing additional user preferences. Supply two color options in the css, and allow user to choose high/low brightness.
HN already has some profile filters, so adding one more might not be a problem, but I can also see how it becomes a slipper-slope of new features.