Scene editor guide. Page 6

Lights - spot

You can control from here the shape of the cone of your light and the way light intensity decreases with the distance from illuminated objects.

When the checkbox "Cutoff=180" is checked the light has no cone (light goes in every direction).
In this state the cutoff angle control has no effect. As soon the checkbox is unchecked the cone angle is determined by the cutoff angle control and the direction of the cone is determined by the direction control.

Tip to center a light on an object:
1) enable just one light
2) start with a wide cutoff angle (90)
3) move the direction coordinates until you see your object
4) gradually decrease the cutoff angle until the object disappears
5) adjust the direction until you see it again
repeat from point 4) until you get the effect you need.

The exponent and the three attenuations affect the way light intensity decreases with the distance of the light from the illuminated objects. Remember that these have effect only if the light is positional (W coordinate not 0). Try them and see what happens.