When I issue `setterm -blank force` or `xset dpms force off` the laptop screen goes blank but the backlight does not turn off.

# lspci -vns 01:00.0
01:00.0 0300: 1002:68c1 (prog-if 00 [VGA controller])
        Subsystem: 103c:1449
        Flags: bus master, fast devsel, latency 0, IRQ 49
        Memory at c0000000 (64-bit, prefetchable) [size=256M]
        Memory at d4000000 (64-bit, non-prefetchable) [size=128K]
        I/O ports at 4000 [size=256]
        Expansion ROM at d4040000 [disabled] [size=128K]
        Capabilities: [50] Power Management version 3
        Capabilities: [58] Express Legacy Endpoint, MSI 00
        Capabilities: [a0] MSI: Enable+ Count=1/1 Maskable- 64bit+
        Capabilities: [100] Vendor Specific Information <?>
        Kernel driver in use: radeon
        Kernel modules: radeon

In the attached logs,

1. Booted without X
2. Ran # setterm -blank force ; sleep 5 ; setterm -blank poke
3. Started X
4. Ran $ xset dpms force off ; sleep 5 ; xset dpms force on