The older PG projectors will display this message every 100 hours of use; it doesn't necessarily mean that it has detected a dirty filter, but it doesn't hurt to check.
Cleaning the Filter
Most projectors have a slot for a sponge-type filter. Simply remove the filter, blow-out the dust, and re-install.
To turn the message off …
- Use the projector remote and press the 'menu' button.
- On the far right of the options showing on the projection, select 'reset'.
- Clear filter hours is the last option. Select that and confirm the reset.
- Use the 'exit' button to move backwards through / quit the menus.