I didn’t believe in this software until I tried it. It started working the first day I used it.
Essentially, it changes the colour temperature of your screen depending on what time of day it is. If it’s daytime, your screen will be normal. If it’s nighttime, it’ll be more red. Apparently there’s a lot of research data to suggest that this helps with sleeping patterns of humans (something to do with the sun). Anecdotally, I can verify that it has helped my sleep patterns immensely.
I just wish it had the incremental colour change option enabled by default. Out-of-the-box, it switches from blue to red quickly after you cross a certain point of day. I like it when it’s more subtly done.
UPDATE! Just a few days after this post, the developer of f.lux updated the software after a period of inactivity. The new features include the ability to go even dimmer during evening hours and a new “movie mode” which disables f.lux for 2.5 hours (long enough for your average movie to play through).