You may create a lamp which lights only in a conic area.
{ conelamp
pos ( 0 , 0 , 0 );
color (1,1,1);
dir ( 0 , 0 , -1 );
ang 0;
}
pos and color are like for the point lamp.
dir
a vector which gives the illumination direction.
ang
an angle which tells how large is the conic area of the lamp.