int set_light(n)
int n;

An object is by default dark. It can be set to not dark by calling
set_light(1). The environment will the also get this light.  The returned
value is the total number of lights in this room.  Note that the value of
the argument is added to added to the light of the current object.  So if
you've done a set_light(1) you can then remove that light with a
set_light(-1).