Many laptops have their screens dimmed after returning from “suspend” and cannot get back to their original brightness. The bug hasn’t been fixed for 3 years. A fix is provided in the bug report by putting something like the following in
<pre class="src src-sh"><span style="color: #eedd82;">brt</span>=<span style="color: #fa8072;">`cat /sys/devices/virtual/backlight/acpi_video0/brightness`</span>
if (( $brt != $abrt )) ; then
echo $abrt > /sys/devices/virtual/backlight/acpi_video0/brightness
Use the following
find /sys/ -iname 'bright'
to see if you need to change the exact path to the files.