Turning on Backlight
adds a backlight to the active sample slot. This button is on by
Left: Backlight on
Right: Backlight off
The effect is most easily
seen with the sample spheres, where the backlight highlights the
lower-right edge of the sphere.
Backlight is especially
useful whenever you're creating
Backlight lets you see and adjust the specular highlight created
by glancing light, which is much brighter on metals.