StayLit is a very simple program that lets you disable
the backlight auto switch off.

To install the program just copy the file 'StayLit.opo'
to anywhere on your Psion 5. It is NOT an application
which needs to go into the System folder.

Run the program by tapping it twice.

Note: If you open the 'Screen' controls in Control Panel
then the backlight timer will get re-enabled; you will
need to run StayLit to turn it off again.