Can I force a greater screen brightness from Windows Command Prompt

Question

I have a Sony Vaio laptop, and it runs windows 7. I know I can adjust screen brightness from the control panel, but I want to force it to be even brighter. Is there a hack, or a way to do this from command prompt?

Answer 1

OK, so here's what I did:

The two commands for setting any power settings are powercfg -SetDcValueIndex and powercfg -SetAcValueIndex, depending if you want to change setting when on batteries or on AC power. This command has format (case insensitive):

POWERCFG -SETDCVALUEINDEX <SCHEME_GUID> <SUBGROUP_GUID> <SETTING_GUID> value

Then we need three GUIDs. Find them by running powercfg -q. The output looks like this (it will be in your system's language):

D:\Users\212579988>powercfg /q
Power Scheme GUID: 381b4222-f694-41f0-9685-ff5bb260df2e  (Balanced)
  Subgroup GUID: fea3413e-7e05-4911-9a71-700331f1c294  (Settings belonging to no subgroup)
    Power Setting GUID: 0e796bdb-100d-47d6-a2d5-f7d2daa51f51  (Require a password on wakeup)
      Possible Setting Index: 000
      Possible Setting Friendly Name: No
      Possible Setting Index: 001
      Possible Setting Friendly Name: Yes
    Current AC Power Setting Index: 0x00000001
    Current DC Power Setting Index: 0x00000001

  Subgroup GUID: 0012ee47-9041-4b5d-9b77-535fba8b1442  (Hard disk)
    Power Setting GUID: 6738e2c4-e8a5-4a42-b16a-e040e769756e  (Turn off hard disk after)
      Minimum Possible Setting: 0x00000000
      Maximum Possible Setting: 0xffffffff
      Possible Settings increment: 0x00000001
      Possible Settings units: Seconds
    Current AC Power Setting Index: 0x00000000
    Current DC Power Setting Index: 0x00000000

...

  Subgroup GUID: 7516b95f-f776-4464-8c53-06167f40cc99  (Display)
    Power Setting GUID: 17aaa29b-8b43-4b94-aafe-35f64daaf1ee  (Dim display after)
      Minimum Possible Setting: 0x00000000
      Maximum Possible Setting: 0xffffffff
      Possible Settings increment: 0x00000001
      Possible Settings units: Seconds
    Current AC Power Setting Index: 0x0000012c
    Current DC Power Setting Index: 0x00000078

    Power Setting GUID: 3c0bc021-c8a8-4e07-a973-6b14cbcb2b7e  (Turn off display after)
      Minimum Possible Setting: 0x00000000
      Maximum Possible Setting: 0xffffffff
      Possible Settings increment: 0x00000001
      Possible Settings units: Seconds
    Current AC Power Setting Index: 0x00000258
    Current DC Power Setting Index: 0x0000012c

    Power Setting GUID: aded5e82-b909-4619-9949-f5d71dac0bcb  (Display brightness)
      Minimum Possible Setting: 0x00000000
      Maximum Possible Setting: 0x00000064
      Possible Settings increment: 0x00000001
      Possible Settings units: %
    Current AC Power Setting Index: 0x00000064
    Current DC Power Setting Index: 0x0000000c

...

Now you need to find and write down:

• current scheme GUID - it's in the first line.
• subgroup GUID for Display - look down for Display
• setting GUID for brightness - look down for Display Brightness

Now put your three GUID values plus desired brightness in percent - lets say 10% - like this:

C:\Users\Mike>powercfg -SetDcValueIndex 381b4222-f694-41f0-9685-ff5bb260df2e 7516b95f-f776-4464-8c53-06167f40cc99 aded5e82-b909-4619-9949-f5d71dac0bcb 10 

And... nothing happened for me! The brightness didn't change! By executing powercfg /q I checked that indeed my new value was stored properly. So I just asked to make my power setting active (even though it was active all the time):

C:\Users\Mike>powercfg -S 381b4222-f694-41f0-9685-ff5bb260df2e

And voila! my screen brightness dimmed to 10%!

Answer 2

I made a batch file that works for english which uses the method above. http://aarongiera.com/change_brightness.bat

for /f "tokens=*" %%i in ('powercfg -q ^| find "Power Scheme GUID"') do set pwrSchm=%%i
set pwrSchm=%pwrSchm:~19,36%

for /f "tokens=*" %%i in ('powercfg -q ^| find "(Display)"') do set dsply=%%i
set dsply=%dsply:~15,36%

for /f "tokens=*" %%i in ('powercfg -q ^| find "(Display brightness)"') do set brtnss=%%i
set brtnss=%brtnss:~20,36%

set /P brightness=Enter % brightness:  %=%

powercfg -SetDcValueIndex %pwrSchm% %dsply% %brtnss% %brightness%
powercfg -S %pwrSchm%

It works, but only on a scale of 0-100. It can't any lower or higher brightness the leds are capable of disappointingly.