Do not depends on kernel with CONFIG_SYSFS_DEPRECATED*=y.
With the new sysfs layout, /sys/class/backlight/* contains only symlinks.
chown -R skips symlinks, keeping device accessible only for root.

Index: gpe-login-0.95/X11/gpe-login.pre-session
===================================================================
--- gpe-login-0.95.orig/X11/gpe-login.pre-session	2008-08-06 21:23:40.000000000 +0000
+++ gpe-login-0.95/X11/gpe-login.pre-session	2009-05-28 13:28:37.000000000 +0000
@@ -57,7 +57,7 @@
 # screen light control #
 
 if [ -d /sys/class/backlight ]; then
-chown -R $USER /sys/class/backlight/*
+chown -R $USER /sys/class/backlight/*/*
 chmod u+rw /sys/class/backlight/*/*
 fi