Mathematical Topics from 3D Graphics - 3D Math Primer for Graphics and Game Development - page 415

Figure 10.30
A point light
effect of the light can be bounded. Section 10.7.2 compares real-world
attenuation with the simplified models commonly used. Point lights can be
used to represent many common light sources, such as light bulbs, lamps,
fires, and so forth.
A spot light is used to represent light from a specific location in a specific
direction. These are used for lights such as flashlights, headlights, and of
course, spot lights! A spot light has a position and an orientation, and
optionally a falloff distance. The shape of the lit area is either a cone or a
pyramid.
A conical spot light has a circular “bottom.” The width of the cone
is defined by a falloff angle (not to be confused with the falloff distance).
Also, there is an inner angle that measures the size of the hotspot. A conical
spot light is shown in Figure 10.31.
Figure 10.31
A conical spot
light