Howto Lower brightness on Apple LCD Monitor? KUbuntu 10.4, KDE System Settings Display; jor

Duncan 1i5t5.duncan at
Tue Jun 22 23:59:26 BST 2010

giovanni_re posted on Tue, 22 Jun 2010 14:26:57 -0700 as excerpted:

> Didn't get an answer on KUbuntu list, so hopefully someone here might
> have a suggestion.
> ==
> I've just installed an Apple Cinema Display (LCD) monitor. This is a 5
> year old monitor. Using KUbuntu 10.4
> The apple website indicates this monitor has: User controls (hardware
> and software):
>   	Display power, system sleep, system wake, brightness and display 
> Brightness is what I want to turn down.
> Looking in the
> KDE System Settings > General > Computer Administration > Display > Size
> & orientation > DVI-0
> there is no adjustment for brightness.
> Anyone know how to decrease brightness on this?
> What sw manages the KDE system settings for Displays?  KDE? X?

Well, with laptops, brightness is usually controlled via the kernel laptop 
driver or ACPI, if not firmware-wired to specific keys in the BIOS.

With desktops/workstations, brightness is normally controlled using the 
monitor hardware/firmware, not software.

However, X, and kde thru X, both can control the /gamma/, which isn't 
exactly brightness, but rather, the color-value-sensitivity-curve. (Gamma 
is a number which answers the question: Is the difference between assigned 
color values at the low end and the high end of the scale the same, or is 
one end more sensitive than the other, and by how much?  The X default is 
linear, a 1.0 gamma, with the Apple default gamma curve of IIRC 2.2 
bulging strongly upward, such that a change in value at the lower end 
changes strength far more than at the upper end, with the MS default 
somewhere in the middle at IIRC 1.8.  A higher gamma will tend to be 
brighter, tho the ends are the same, because the middle values are far 
stronger.  Thus, pictures that look good at the Apple default of 2.2 tend 
to be too dark, they look "underexposed" to use a photography term, at the 
X default of 1.0, while those that look good at the X 1.0 default, usually 
look way too bright and washed out, "overexposed", at the Apple 2.2 

In kde 4.4, The kde setting for gamma is in kcontrol aka system-settings, 
computer admin, display, gamma.  It's also available by running kgamma, 
directly (from krunner or the like).  The associated kde help is quite 
good at guiding you step-by-step thru the process of choosing a good 

To permanently change the system X gamma setting, use xorg.conf.  See the 
xorg.conf manpage, monitor section, gamma keyword.

Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

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