Locked cellphone display illumination?

When using cellphone display as small portable light source there is a common problem that lcd display backlight turns off after certain period of time.

Options:
1. Try locking cellphone illumination by entering game or application.
2. If this won't help you can check if phone has some "system" menus which may be accessible by entering special code. System menus will keep illumination.


Usage examples:
-pedestrian light
-light when there is no other source (in forest)
-ambient light
-long search for dropped keys in dark