From the NannyMUD documentation

LAST CHANGE

2000-01-15

FUNCTION

NAME
        test_can_see - Check of the living can see here.


LOCATION
	/obj/living_functions

SYNTAX
	varargs int test_can_se(int silent)

DESCRIPTION
	This function is used to find out if the living can see at the
	current location. It checks light levels, blindness, and
	nightvision. 


RETURN VALUES
	The function returns non-zero if the living can see.