For people who are very sensitive to brightness or bright light, it can be difficult to read on a smartphone display, even though the brightness level is down to the minimum.
Therefor, Apples iOS operating system has a built in feature, that allows to reduce the brightness level below the minimum for normal use.
Here is a small how to:
1. Open the settings app and tap on "General"
2. Tap on "Accessibility"
3. Tap on "Zoom"
4. Tap on "Zoom Filter" and select "Low Light"
Hope we could help.