having used these programs for many years: the color casts caused by f.lux don't typically match surrounding light, even when everything switches roughly simult

having used these programs for many years: the color casts caused by f.lux don't typically match surrounding light, even when everything switches roughly simultaneously (which is rare, because of all kinds of artificial sources that are on/off unpredictably to f.lux). I regularly set my night schedule well in advance of sunset, and it's not a problem; you always keep screen out of direct sunlight, and so far I've also managed to avoid direct sunlight in the visual vicinity simply because the contrast is too great. And that means that even in well-lit rooms, it's fine to have a screen slowly turn red. While it takes some getting used to - the same can be said of f.lux in general. To each their own of course - if it bothers you, don't do that ;-). But from personal experience I can assure you that not everyone minds a reddish screen before sunset (honestly, many visitors don't even notice unless there's some other screen right next to it).