I used the
acpi_osi= trick to make Xubuntu 14.04 work with my newly acquired CF-52 Mk 1 Toughbook. Among other things, this enabled it to control the LCD backlight brightness. This mostly works fine, but at 50%, the backlight brightness stops increasing.
These laptops are notorious for failing CCFL backlights. However, I am not experiencing flaring/flashing on startup, dimming over time, or inconsistent brightness. Is it possible that I have either limited the brightness to 50% somewhere without realizing it?