I can't go over 4 in a totally dark room. It hurts my eyes. I remember one time my hubby gave me his iphone in a dark bedroom to show me something. I grabbed it and it was like looking in the sun. I saw flashes for a while after. Ouch that hurt.
. He had his light on daytime setting I guess.
Before I got my paperwhite, I used my old fire for a while and even the darkest setting wasn't dark enough for me, I had to get a dim app.
When I first got my paperwhite I constantly fiddled with the light settings. 3, 12, 17. Now that I finally settled, I keep it at 4-5 at all times. Day and evening.
Even if I am in bed its at 4. I don't read though in a totally dark room so I have a small lamp on the side.
For me I want the PW to be readable at all times, without me having to fiddle. 4 does that. Or 5. Right now its at 4 and it stays for a while.
I read a lot while watching TV. So I have a side lamp and its dark-ish in the room. With my kindle keyboard, I used to have to lean towards the light, which hurt my back and neck after a while. On setting 4 with the PW, it gets me enough light to not have to do that.
I never really had any issues with the e-ink screen in bright light, so I don't need the light on the PW any higher either. But its fantastic when it gets darker inside, or when I am not near a window, outside, or at night.
Now that I have had my light at low settings all the time, I tried putting it up at 17 just to see and I don't like it. It looks like its lit. I just want it to look a bit less dingy than the e-ink screen and more like paper. The moment I notice its lit its way to high.