I had the same problem and used one of the dark overlay tools that the author of the article criticizes to bring it down further than 0% brightness. But that trick also messes up color depth. I've since switched to an iMac, and the nice thing is that while the display can go very bright, when you dial down the brightness to the lowest value it is very dim to the point of being hard to read in daylight.
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.
