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I have tried changing the brightness.

added echo 4 > /sys/class/backlight/intel_backlight/brightness to /etc/rc.local

But it is temporary change & still getting black screen while login.

How can we set the brightness settings permanently?

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This information is not enough , we need information about your PC and Display driver details.Thank you. – Raja Mar 28 '13 at 10:07
up vote 1 down vote accepted

Can you try editing that line in /etc/rc.local to instead be:

echo 4 > /sys/class/backlight/acpi_video0/brightness

That's what I have in my rc.local file, and it works like a charm at every boot no matter what.

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yes it is working...thankyou :) finally got fixed – Vimal Mar 28 '13 at 3:25
Glad to hear that :) Please mark my answer as accepted if it actually helped! – oaskamay Mar 28 '13 at 3:41

Have you tried going to startup Applications in the dash.
Add a new startup program "Brightness Level" and add in the command line: xbacklight -set XX
XX being the level you wan at boot. I think it's a 100 scale. I've set mine at 60.

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I have tried this today. Restarted my laptop to get it didn't work. Again i am getting the blackscreen while login...I need to press brighntess key for viewing the login screen. is there anything to do with graphics drivers? – Vimal Mar 28 '13 at 3:16

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