linux/shell command to control screen brightness in android

I am working on a kiosk project using an android tablet. If there is no input power to the kiosk for a long time, then the tablet will eventually shut down. In order to auto-reboot the tab when the power comes back, I modified the code in my tabs battery animation file (ipod) using: #!/system/bin/sh sleep 300 /system/bin/reboot However, during the sleep period (shown above), the tabs screen remains in the ON state (and hence takes longer retries for the tab to charge and bootup). I need to turn the screen OFF. What is the command I should use prior to the sleep command to turn my tabs screen OFF during the charging/bootup stage.