% ls -l /sys/class/backlight
/sys/class/backlight:
total 0
lrwxrwxrwx 1 root root 0 Jan 15 13:02 acpi_video0 -> ../../devices/pci0000:00/0000:00:02.0/backlight/acpi_video0
lrwxrwxrwx 1 root root 0 Jan 10 01:01 intel_backlight -> ../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight
% ls -lR /sys/class/backlight/*/
/sys/class/backlight/acpi_video0/:
total 0
-r--r--r-- 1 root root 4096 Jan 15 19:56 actual_brightness
-rw-r--r-- 1 root root 4096 Jan 15 19:56 bl_power
-rw-r--r-- 1 root root 4096 Jan 15 13:02 brightness
lrwxrwxrwx 1 root root    0 Jan 15 19:56 device -> ../../../0000:00:02.0
-r--r--r-- 1 root root 4096 Jan 15 19:56 max_brightness
drwxr-xr-x 2 root root    0 Jan 15 19:56 power
lrwxrwxrwx 1 root root    0 Jan 15 19:56 subsystem -> ../../../../../class/backlight
-r--r--r-- 1 root root 4096 Jan 15 19:56 type
-rw-r--r-- 1 root root 4096 Jan 15 19:56 uevent

/sys/class/backlight/acpi_video0/power:
total 0
-rw-r--r-- 1 root root 4096 Jan 15 20:09 async
-rw-r--r-- 1 root root 4096 Jan 15 20:09 autosuspend_delay_ms
-rw-r--r-- 1 root root 4096 Jan 15 20:09 control
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_active_kids
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_active_time
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_enabled
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_status
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_suspended_time
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_usage

/sys/class/backlight/intel_backlight/:
total 0
-r--r--r-- 1 root root 4096 Jan 10 01:01 actual_brightness
-rw-r--r-- 1 root root 4096 Jan 15 19:56 bl_power
-rw-r--r-- 1 root root 4096 Jan 10 01:01 brightness
lrwxrwxrwx 1 root root    0 Jan 15 19:56 device -> ../../card0-LVDS-1
-r--r--r-- 1 root root 4096 Jan 15 15:52 max_brightness
drwxr-xr-x 2 root root    0 Jan 15 19:56 power
lrwxrwxrwx 1 root root    0 Jan 10 01:01 subsystem -> ../../../../../../../class/backlight
-r--r--r-- 1 root root 4096 Jan 15 19:56 type
-rw-r--r-- 1 root root 4096 Jan 10 01:01 uevent

/sys/class/backlight/intel_backlight/power:
total 0
-rw-r--r-- 1 root root 4096 Jan 15 20:09 async
-rw-r--r-- 1 root root 4096 Jan 15 20:09 autosuspend_delay_ms
-rw-r--r-- 1 root root 4096 Jan 15 20:09 control
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_active_kids
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_active_time
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_enabled
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_status
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_suspended_time
-r--r--r-- 1 root root 4096 Jan 15 20:09 runtime_usage
% for file in $(find /sys/class/backlight/*/ -type f); do echo $file; cat $file; echo; done
/sys/class/backlight/acpi_video0/uevent

/sys/class/backlight/acpi_video0/bl_power
0

/sys/class/backlight/acpi_video0/brightness
7

/sys/class/backlight/acpi_video0/actual_brightness
7

/sys/class/backlight/acpi_video0/max_brightness
8

/sys/class/backlight/acpi_video0/type
firmware

/sys/class/backlight/acpi_video0/power/async
disabled

/sys/class/backlight/acpi_video0/power/runtime_status
unsupported

/sys/class/backlight/acpi_video0/power/runtime_usage
0

/sys/class/backlight/acpi_video0/power/runtime_active_kids
0

/sys/class/backlight/acpi_video0/power/runtime_enabled
disabled

/sys/class/backlight/acpi_video0/power/control
auto

/sys/class/backlight/acpi_video0/power/runtime_suspended_time
0

/sys/class/backlight/acpi_video0/power/runtime_active_time
0

/sys/class/backlight/acpi_video0/power/autosuspend_delay_ms
cat: /sys/class/backlight/acpi_video0/power/autosuspend_delay_ms: Input/output error

/sys/class/backlight/intel_backlight/uevent

/sys/class/backlight/intel_backlight/bl_power
819863552

/sys/class/backlight/intel_backlight/brightness
1202

/sys/class/backlight/intel_backlight/actual_brightness
1202

/sys/class/backlight/intel_backlight/max_brightness
4882

/sys/class/backlight/intel_backlight/type
raw

/sys/class/backlight/intel_backlight/power/async
disabled

/sys/class/backlight/intel_backlight/power/runtime_status
unsupported

/sys/class/backlight/intel_backlight/power/runtime_usage
0

/sys/class/backlight/intel_backlight/power/runtime_active_kids
0

/sys/class/backlight/intel_backlight/power/runtime_enabled
disabled

/sys/class/backlight/intel_backlight/power/control
auto

/sys/class/backlight/intel_backlight/power/runtime_suspended_time
0

/sys/class/backlight/intel_backlight/power/runtime_active_time
0

/sys/class/backlight/intel_backlight/power/autosuspend_delay_ms
cat: /sys/class/backlight/intel_backlight/power/autosuspend_delay_ms: Input/output error

%