Laptops :: laptop backlight problems

Is there a good, generic solution for turning a laptop's backlight on and off that works for multiple types of laptops? I want to be able to turn it on and off "on demand" from a script.

I spent a long time trying to force off the backlight of my Toshiba 550CDT using setterm commands from a text terminal (outside X), or xset dpms / xset s commands within X. I could get the screen to go black, but the backlight always remained on.

Finally I recompiled the kernel, enabling the APM option to turn off the LCD when the virtual console screen blanker kicks in. This worked (hooray), so now I can force the backlight off in 60 seconds with setterm -blank 1 from a console.

But now I have the opposite problem, with my modified kernel the backlight also turns off after 30 minutes of inactivity in X windows! I've tried "setterm -blank 0", "xset s off", "xset -dpms" and every other thing I could think off to turn off power saving or screensaving, but it made no difference. I read every relevant thread I could find in these forums and elsewhere. I even wrote a script to shove some bytes into /dev/mouse every 60 seconds to make X think the mouse was moving, thereby preventing the screensaver, but again it made no difference.

At this point I'm not sure what's turning off the LCD, but I don't think it's anything related to the BIOS since it only started happening after I recompiled the kernel. I'm at my wit's end now. Can anybody think of anything else clever I might try to prevent this mysterious LCD shutoff after 30 minutes?

original here.