To list available controls, type:

 # ddccontrol -p 

This probes for available monitors, then takes the first probed monitor and lists controls supported by it. This should give you an output like this (this example uses a Samsung Syncmaster 173P and a nVidia GeForce FX 5700):

 ddccontrol version 0.1 Copyright 2004 Oleg I. Vdovikin (oleg-at-cs.msu.su) Copyright 2004 Nicolas Boichat (nicolas-at-boichat.ch) This program comes with ABSOLUTELY NO WARRANTY. You may redistribute copies of this program under the terms of the GNU General Public License. Device : pci:01:00.0-0 Error while reading write message answer: Bad message Reading EDID 0x50 failed. Device : pci:01:00.0-1 Device : pci:01:00.0-2 Detected monitors : - Device : pci:01:00.0-1 DDC/CI supported : Yes Monitor Name : Samsung SyncMaster 173P (DVI) Input type : Digital (Automatically selected) - Device : pci:01:00.0-2 DDC/CI supported : Yes Monitor Name : NEC Multisync 2080UX+ Input type : Analog Reading EDID and initializing DDC/CI at bus pci:01:00.0-1... Device : pci:01:00.0-1 EDID readings: Plug and Play ID: SAM00E2 [Samsung SyncMaster 173P (DVI)] Input type: Digital = Samsung SyncMaster 173P (DVI) > Color settings > Brightness and Contrast > id=brightness, name=Brightness, address=0x10, delay=-1ms, type=0 supported, value=55, maximum=100 > id=contrast, name=Contrast, address=0x12, delay=-1ms, type=0 supported, value=60, maximum=100 > id=magicbright, name=Magic Bright Mode, address=0xdc, delay=-1ms, type=2 Possible values: > id=text - name=Text, value=1 > id=internet - name=Internet, value=2 > id=entertain - name=Entertain, value=3 > id=custom - name=Custom, value=4 supported, value=4, maximum=4 > Others > Restore defaults > id=defaults, name=Restore Factory Defaults, address=0x4, delay=-1ms, type=1 Possible values: > id=default - name=Restore Factory Defaults, value=1 supported, value=0, maximum=1 > id=defaultluma, name=Restore Brightness and Contrast, address=0x5, delay=-1ms, type=1 Possible values: > id=default - name=Restore Brightness and Contrast, value=1 supported, value=0, maximum=1 > id=settings, name=Settings, address=0xb0, delay=-1ms, type=1 Possible values: > id=store - name=Save Current Settings, value=1 > id=restorefactory - name=Restore Factory Settings, value=2 supported, value=0, maximum=2 > Input settings > id=inputsource, name=Input Source Select, address=0x60, delay=-1ms, type=2 Possible values: > id=analog - name=Analog, value=1 > id=digital - name=Digital, value=3 supported, value=3, maximum=3 > Power control > id=dpms, name=DPMS Control, address=0xd6, delay=-1ms, type=2 Possible values: > id=on - name=On, value=1 > id=standby - name=Standby, value=4 supported, value=1, maximum=4 

The lines concerning brightness in the available controls list are:

 > id=brightness, name=Brightness, address=0x10, delay=-1ms, type=0 supported, value=55, maximum=100 

The important elements are address (here: 0x10), current value (55) and maximum value (100).

To change the brightness value to 70/100, type:

 ddccontrol -p -r 0x10 -w 70 

The last lines of the output should be:

 Writing 0x10, 0x46(70)... Control 0x10: +/70/100 [Brightness]