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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?

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Do your Fn + <key> brightness controls not work? –  kobaltz Sep 9 '12 at 21:27
    
There's a powercfg command that allows you to change the values of the brightness index but it's used for specific themes (Ex. -SETACVALUEINDEX is used when the computer is plugged in). I don't believe this is what you're looking for... –  mdeitrick Sep 10 '12 at 0:31
    
I guess there aren't any parameters for powercfg.cpl... good question +1. I was wondering the same thing about adjusting the speed of the fan through command prompt. –  mdeitrick Sep 10 '12 at 0:32
    
Your title seems to ask a different question that the description - if you're just after a way to increase screen brightness, there is a hack for a Sony laptop here but I'm not sure if this will work forum.notebookreview.com/sony/… –  Dave Sep 10 '12 at 12:13
    
I would use something like Process Monitor and see if any registry settings were changed when you use the control panel applet. you can then use reg to read/set registry keys from the command line –  Sean Cheshire Sep 11 '12 at 13:28

2 Answers 2

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 is in your system's language, it's in Polish here):

C:\Users\Mike>powercfg /q
Identyfikator GUID schematu zasilania: 381b4222-f694-41f0-9685-ff5bb260df2e  (Zrównowazony)
  Identyfikator GUID podgrupy: fea3413e-7e05-4911-9a71-700331f1c294  (Ustawienia, które nie naleza do podgrupy)
    Identyfikator GUID ustawienia zasilania: 0e796bdb-100d-47d6-a2d5-f7d2daa51f51  (Wymagaj hasla przy wznawianiu)
      Indeks mozliwego ustawienia: 000
      Przyjazna nazwa mozliwego ustawienia: Nie
      Indeks mozliwego ustawienia: 001
      Przyjazna nazwa mozliwego ustawienia: Tak
    Biezacy indeks zasilania pradem przemiennym: 0x00000000
    Biezacy indeks zasilania pradem stalym: 0x00000000

  Identyfikator GUID podgrupy: 0012ee47-9041-4b5d-9b77-535fba8b1442  (Dysk twardy)
    Identyfikator GUID ustawienia zasilania: 6738e2c4-e8a5-4a42-b16a-e040e769756e  (Wylacz dysk twardy po)
      Minimalne mozliwe ustawienie: 0x00000000
      Maksymalne mozliwe ustawienie: 0xffffffff
      Mozliwy przyrost ustawien: 0x00000001
      Jednostki mozliwych ustawien: Sekundy
    Biezacy indeks zasilania pradem przemiennym: 0x000004b0
    Biezacy indeks zasilania pradem stalym: 0x00000258

..and so on.

Now you need to find and write down:

  • current scheme GUID - it's in the first line.
  • subgroup GUID - in English it would be named screen
  • setting GUID - in English it would be screen 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%!

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Nice first post! –  slm Dec 29 '12 at 16:08
    
Great post here. Some clarification: For English, the current scheme is referred to as Power Scheme, the subgroup GUID for screen settings is labeled Display and the setting GUID for brightness is labeled Display brightness. The following command will get all the necessary data for you: powercfg -q | find "Power Scheme GUID" & powercfg -q | find "(Display)" & powercfg -q | find "(Display brightness)" –  Iszi Jun 7 '13 at 16:25
    
I tried this and it didn't work. Might it need to be run from an elevated command prompt? –  Iszi Jun 7 '13 at 16:39
    
I think I figured out my problem. It looks like this won't work if your settings are locked down by GPO. –  Iszi Jun 7 '13 at 17:09

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.

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