It might be placebo, but I've noticed a pretty dramatic drowsiness set in immediately following the f.lux "sunset." A lot of the time I will turn it off so I can stay up and get things done. If that's what one experiences at 5pm, I'd call that unusable.

New version has "working late" mode. http://puu.sh/7lImw.png

Likewise. As with a pomodoro ending and the bell rining, the sun setting on PyCharm stops me working. All sorts of chemistry going on.

It was absolutely unusable. Here in the north you would get two hours of sunlight during the winter, and f.lux would work accordingly.

Similarly in the summer, you would get only a few hours of darkness, making f.lux almost completely useless except for a few months of the year.

Not dramatic - having your screen turn orange at 6pm is unusable. I'm going to work until 11 or 12pm. Let met set it so I start winding down an hour or two before I go to sleep. It does decrease the contrast of text, making it harder to read.

To be fair, I think the flux developers would tell you to stop working a lot earlier than 11pm.

No, you just don't work until 11pm on them. You go to bed earlier, wake earlier, work on them at a different time, and have a more natural (i.e. solar-based) sleep cycle.

Having side projects and staying up too late do not need to be synonymous.

When sunrise is 8:30 and sunset is 16:45 it's rather hard to work a full time job and a side project simultaneously in daylight hours.

I too found flux unusable.

The new stepped changes and options including "Working Late" should help a lot.