first check BIOS settings. My thinkpads provides in BIOS settings for brightness in case of with or without AC power. Otherwise this is an ACPI case. There are a lot of notebooks having non ACPI compliant DSTN table, which means Linux kernel won't be able to provide all ACPI functions available.
Did you take a look at Linuxlaptop
? There you can find additional information for various types of notebooks on Linux.