I found putting one of those Philips Hue light strips behind the monitor helped tremendously. If I set its brightness and temperature to a dim warm setting, the dimly-lit wall right behind the monitor makes mid-range screen brightness work just fine (eyes accomodate to the higher overall brightness, so the monitor needs to be brighter to "fit in", but I still perceive the whole scene as dimly-lit) and the color temperature seems to work well for me, I still get tired and sleepy. I can even control the light using the Hue bridge's REST API, so it's easy to automate as well.
That would help indeed, and so does keeping the lights on at a high level. But my 4K is so bright at 0% that it feels too bright for me even with the brightest artificial light I have :) Only in daylight it's OK (and I still keep it at 0% then!).
But there is another reason I don't always have lights on. I live in Barcelona where it gets hot in summer and I don't have AC. So at night when the temperature outside is lower than inside I leave all the windows open to cool the house. If I have lights on it attracts bugs. So I stay mainly in the dark.
