iBook blacks out after 5 minutes of non-use

My iBook gets a black screen if it is left open and not used for about 5 minutes.
Dude wrote on :
My iBook gets a black screen if it is left open and not used for about 5 minutes. As long as I am using it it is fine. If I close the cover to force sleep it is OK. Any ideas?
Chas replied on :

Dude wrote:

My iBook gets a black screen if it is left open and not used for about 5 minutes. As long as I am using it it is fine. If I close the cover to force sleep it is OK. Any ideas?

System Preferences | Energy Saver | Sleep and look at "Put the display to sleep when the computer is inactive for:"

=:~)