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Old 04-02-2008, 01:56 PM   #1
Completely Clueless
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How to adjust screen brightness (Fedora)


Hi guys,

This will sound like a stupid question, but I'm practically getting a tan off my screen. How does one adjust the brightness of the display in a laptop (Fujitsu Siemens Esprimo)running Fedora 8? I've tried using the 2-key function combination that works with various live CD distros no problem, yet on this (permanent) installation, any attempt to dim the (maximally bright) display reverts to maximum again within a fraction of a second. Can anyone assist?

Thanks,

CC.

Last edited by Completely Clueless; 04-02-2008 at 01:57 PM. Reason: typo
 
Old 04-02-2008, 02:51 PM   #2
Mega Man X
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I think the command xgamma could help. Read the manpage I linked and try something like xgamma -gamma 0.5 in a terminal. Can't test it now, but I bet you will figure it out if the command doesn't work

Regards!
 
Old 04-02-2008, 06:55 PM   #3
brightwindow
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I thought it would it quite easy.
 
Old 04-04-2008, 05:20 PM   #4
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Quote:
Originally Posted by Mega Man X View Post
I think the command xgamma could help. Read the manpage I linked and try something like xgamma -gamma 0.5 in a terminal. Can't test it now, but I bet you will figure it out if the command doesn't work

Regards!
Hi there and thanks for the suggestion. Sorry about the delay, but I've been fighting other demons in WhineDos on another machine. :-(

Right! Well, I entered your suggested command above in the terminal and it appeared to have been executed, because it echoed back something like (and i'm paraphrasing) was Red: 1, blue: 1, green: 1;
now Red: 0.5, blue: 0.5, green: 0.5

indicating (to my simple mind at any rate)a halving of the total of white light, but it made absolutely no difference to the screen brightness.

I didn't budget for the cost of welding goggles in my switchover to Linux, so... any other suggestions?

tnx,

CC.

Last edited by Completely Clueless; 04-04-2008 at 05:25 PM. Reason: misleading terminology
 
Old 04-05-2008, 10:34 AM   #5
ewaller
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Completely,

The only problem with changing the gamma is that you are only stopping down the LCD, reducing the amount of light that passes from the CCFL (Cold Cathode Florescent Lamp). This reduces the number of colors, gray scales and range of luminance available to you. It is a lot like turning the contrast on yout television down.

Furthermore, it does nothing to reduce the power used by the backlight thus providing no reduction in heat load, nor does it help your battery life, and it does not inrease your "green" karma.

Most of the laptops I have worked with have (or can have) an entry in the /proc file system that allows the control of backlight brightness

Here is an example from my system:

ewaller@lappy ~ $ ls -l /proc/toshiba_smi
total 0
-rw-rw-rw- 1 root root 0 Apr 5 08:25 aerial
-rw-rw-rw- 1 root root 0 Apr 5 08:25 brightness
-rw-rw-rw- 1 root root 0 Apr 5 08:25 display
-rw-rw-rw- 1 root root 0 Apr 5 08:25 fn
-rw-rw-rw- 1 root root 0 Apr 5 08:25 fn_f5
-rw-rw-rw- 1 root root 0 Apr 5 08:25 kill_switch
ewaller@lappy ~ $ cat /proc/toshiba_smi/brightness
brightness = 7
ewaller@lappy ~ $ echo 4 > /proc/toshiba_smi/brightness
ewaller@lappy ~ $ cat /proc/toshiba_smi/brightness
brightness = 4

This support can enabled in the kernel. The fact that it dims, and then reverts makes me think this may be enabled. Take a look in /proc and look for things like smi, Fujitsu, acpi. Drill down and see if you can find something related to brightness. If you do, use cat to look at the current value, and echo (see above) to try to change it.

Good Luck
e waller
 
Old 04-05-2008, 05:53 PM   #6
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Quote:
Originally Posted by ewaller View Post
Completely,

The only problem with changing the gamma is that you are only stopping down the LCD, reducing the amount of light that passes from the CCFL (Cold Cathode Florescent Lamp). This reduces the number of colors, gray scales and range of luminance available to you. It is a lot like turning the contrast on yout television down.

Furthermore, it does nothing to reduce the power used by the backlight thus providing no reduction in heat load, nor does it help your battery life, and it does not inrease your "green" karma.

Most of the laptops I have worked with have (or can have) an entry in the /proc file system that allows the control of backlight brightness
I'm afraid this doesn't appear applicable. My laptop doesn't have a backlit LCD screen (haven't seen one of those for years) but rather a TFT one.
Thanks for trying to help, though.

CC.
 
Old 04-05-2008, 07:50 PM   #7
ewaller
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TFTs are great --most modern laptop displays are TFT. The TFT LCD has greater transmissivity of light because TFT structure provides a greater optical aperture -- but it is not self luminescent. TFT (Thin Film Transistor) LCD panels are still just programmable attenuators that require a backlight. Predominately, these backlights are CCFL, although LEDs are coming on strong. For now CCFLs hold the efficiency and cost edge.

The only technologies that I know of that do not require a backlight are LED matrix, Plasma, or OLED. The first two are power hungry and are not applicable to laptops, OLEDs are not quite ready for production.

Last edited by ewaller; 04-05-2008 at 07:52 PM. Reason: typo
 
Old 04-06-2008, 06:33 AM   #8
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Quote:
Originally Posted by ewaller View Post
TFTs are great --most modern laptop displays are TFT. The TFT LCD has greater transmissivity of light because TFT structure provides a greater optical aperture -- but it is not self luminescent. TFT (Thin Film Transistor) LCD panels are still just programmable attenuators that require a backlight. Predominately, these backlights are CCFL, although LEDs are coming on strong. For now CCFLs hold the efficiency and cost edge.

The only technologies that I know of that do not require a backlight are LED matrix, Plasma, or OLED. The first two are power hungry and are not applicable to laptops, OLEDs are not quite ready for production.
Oh! Sorry I had no idea they functioned in this way. So the screens are always maximally backlit? Crumbs, that's a really inefficient set-up, I must agree. I always wondered why turning down the brightness never seemed to make any real impression on battery life!

Thanks for the lesson; I'll give it another shot and post back in due course!

CC.
 
  


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