I would have to agree that the PW does induce some eye-ache even at the lowest settings. For me, it's mainly because i find that the contrast suffers in a totally dark environment and i need to strain more to see the text.
As i increase the light, i find that the screen can become too bright and hurt my eyes.
Therefore, I find the best compromise is a very faint external room light, with PW set to about 4 on the scale.
During daytime, the PW clearly excels, with a whiter screen (setting 15)