I added this line to my rc.local to allow normal user to control thinklight trough sysfs

bowo@pcxthinkslack:~$ tail /etc/rc.d/rc.local -n2
# allow normal user to turn thinklight off/on trough shell
chmod 666 /sys/class/leds/tpacpi::thinklight/brightness

Create shell script to control thinklight from sysfs. When called, it will turn thinklight on/off

bowo@pcxthinkslack:~$ cat /usr/local/bin/toogle-thinklight.sh
#!/bin/bash
echo `cat  /sys/class/leds/tpacpi::thinklight/brightness | grep -c 0` > /sys/class/leds/tpacpi::thinklight/brightnes

Just for fun, I create also thinklight svg icon using inkscape :) and create thinklight.desktop that calls the shell script: 

bowo@pcxthinkslack:~$ cat Apps/thinklight.desktop
[Desktop Entry]
Comment[fr]=
Comment=
Comment[en]=
Exec=/usr/local/bin/toogle-thinklight.sh
GenericName[fr]=Toogle IBM/Lenovo Thinklight on-off
GenericName=Toogle IBM/Lenovo Thinklight on-off
GenericName[en]=Toogle IBM/Lenovo Thinklight on-off
Icon=/home/bowo/Pictures/svg ku/thinklight.svg
MimeType=
Name[fr]=Thinklight Control
Name=Thinklight Control
Name[en]=Thinklight
Path=
StartupNotify=false
Terminal=false
TerminalOptions=
Type=Application
X-DBUS-ServiceName=
X-DBUS-StartupType=
X-KDE-SubstituteUID=false
X-KDE-Username=

And finally, attach .desktop file into KDE panel