My latpad screen is too light, that cause my eye is very imcomfortable. So I spend time to hanle this problem. At result , I find the follow  method:

1. open the following file on the root user.

/etc/udev/rules.d/81-backlight.rules

2. In the end of the file add following code.

#Set backlight level to 3

SUBSYSTEM=="backlight", ACTION=="add", KERNEL=="acpi_vido0", ATTR{brightness}=="8"

3. reboot your system.

You will find it is work.

This  rules sets the backlight level to a fixed value.

If you have any question,please kick

https://wiki.archlinux.org/index.php/Backlight

Besides, my os is centos 7.0. my latpad is acr 4750.

Good for you,thanks.

Adjusting backlight to a fixed level.