I have tried using f.lux several times as it is a recurring theme on HN, but it just does not work for me. All it does is give everything a red tinge, but the light intensity remains the same. I feel like it is cooking my eyeballs and blurring my vision.

I have working alternatives now neither of which work well with multi-screens and neither of which are sophisticated as f.lux, but they do reduce the intensity of my screens which is what I want.

One is "Dimmer" which I use on my left screen and the other is the built in Nvidia tool to reduce brightness, contrast/gamma etc, which I use on my right screen. Pretty primitive but works for me.