Screen Brightness Stuck on high on an HP dv7t laptop

Question

I have an otherwise fully-functioning install of Ubuntu 12.04 on my HPdv7t laptop.

When I press the 'brightness buttons' on the keyboard the associated images appear on my screen to say I am increasing/decreasing the screen brightness. When I go into "System Settings" I can move the 'brightness slider bar' up and down.

But none of that changes the fact that my screen is stuck on the highest brightness setting.

ANY clues on how to fix this would be greatly appreciated. This giant 17-inch monitor is blinding, and this is making it hard to code for any length of time.

Answer 1

I own Acer Aspire 5755g and I had the same problem with backlight of my screen. My PC has Nvidia GT540M. I read previous answer and found out that on my pc this advice works but i need to run some different command instead of

echo n > /sys/class/backlight/acpi_video0/brightness 

I have to change it to

echo 250 > /sys/class/backlight/intel_backlight/brightness

for example, where 250 is my desired backlight value.

I consider it is because of hybrid graphics in notebooks like mine, so backlight controlled through intel builtin controller.

In such case do cat /sys/class/backlight/intel_backlight/brightness and you'll see your current value of brightness, in my case it was 976 change it with ypur desired level,be aware that if you'll set it to 0 your backlight will be turned off!

Adjust value trying different values between 1 and 976 , 1- means almost turned off backlight and 976 is max value in my system.(If you set it to 0 backlight is turned off, and you can't see anything! of course you can change it again and if you'll reboot it restore to it's config value e.g. max) If you'll try to set value more than maximum it just returns error and nothing changes. To set backlight value at startup add

echo 250 > /sys/class/backlight/intel_backlight/brightness

line to your /etc/rc.local file before exit command.

Also we can enable hotkeys to change backlight manualy in a comfortable way. As for me, I made my hotkeys scripts of scripts for asus laptops placed in /etc/acpi directory. You need 2 scripts - one to increase brightness, another for decreasing, both are placed in /etc/acpi direstory. Also we need to set these scripts to trigger on hotkeys events, it's done via changing files in /etc/acpi/events directory. In my case their names and contents are:
/etc/acpi/events/asus-brightness-down

event=video DD03 00000087 00000000
action=/etc/acpi/asus-brn-down.sh

/etc/acpi/events/asus-brightness-up

event=video DD03 00000086 00000000
action=/etc/acpi/asus-brn-up.sh

where /etc/acpi/asus-brn-down.sh and asus-brn-up.sh are names of our scripts to decrease and increase brightness
Contents of mine /etc/acpi/asus-brn-down.sh

#!/bin/sh
# this is for acer aspire 5755G :)
KEYS_DIR=/sys/class/backlight/intel_backlight

test -d $KEYS_DIR || exit 0

MIN=1
# i set MIN to 1 to almost turn off backlight, but you can set a better one value, 50 for examlple
MAX=$(cat $KEYS_DIR/max_brightness)
VAL=$(cat $KEYS_DIR/brightness)

VAL=$((VAL-25))

if [ "$VAL" -lt $MIN ]; then
VAL=$MIN
fi

echo $VAL > $KEYS_DIR/brightness

and contents of mine /etc/acpi/asus-brn-up.sh

#!/bin/sh
# this is for acer aspire 5755G :)
KEYS_DIR=/sys/class/backlight/intel_backlight
test -d $KEYS_DIR || exit 0
MIN=1
MAX=$(cat $KEYS_DIR/max_brightness)
VAL=$(cat $KEYS_DIR/brightness)
# I decided to increase brightness by 25 per keypress but you can change it to 50 or even 1 if you like
    VAL=$((VAL+25))

if [ "$VAL" -gt $MAX ]; then
    VAL=$MAX
fi

echo $VAL > $KEYS_DIR/brightness

thats all ;)

Answer 2

I had the same problem on a T61 with Nvidia Quadro NVS 140M graphics card.

Switching the drivers from "current version [recommended]" to "version 173" solved the problem.

Answer 3

Incase anyone else stumbles upon this question, like I did, there are some alternative solutions as well.

If the above command, echo 250 > /sys/class/backlight/intel_backlight/brightness, worked for you than the following two suggestions should also work.

Some solutions have been to re-install bash, sudo apt-get install --reinstall bash and others have been to modify grub, making the changes last through reboots, as outlined below:

1. Edit grub with sudo gedit /etc/default/grub
2. Inside of GRUB_CMDLINE_LINUX put acpi_backlight=vendor acpi_osi=linux video.brightness_switch_enabled=1, so it looks something like GRUB_CMDLINE_LINUX="acpi_backlight=vendor acpi_osi=linux video.brightness_switch_enabled=1".
3. Save and close the file
4. Update grub with sudo update-grub
5. Restart your computer.

For more information, see https://bugzilla.redhat.com/show_bug.cgi?id=753012

Answer 4

This is a known problem (if I remember right) against most laptops, they either reset to 0 or to 10. Either way, you can fix this issue by doing sudo vim /etc/rc.local and placing the following in there:

# n should be changed to the number.
echo n > /sys/class/backlight/acpi_video0/brightness

If you need to find out what your favourite number is, then you should first adjust your screen and then do sudo cat /sys/class/backlight/acpi_video0/brightness and use that number. Note: You might have trouble doing cat and echo with sudo, if you do do sudo su and then do it.