To show an application of the Fresnel lens.
Fresnel and normal flashlights.
A "Fresnel flashlight" has a Fresnel lens covering the central area of the glass, causing light which would normally spread out over a large cone to be focused into a nearly parallel beam. Unfortunately, when you compare the light output of this Fresnel flashlight with that of a normal flashlight it really doesn't seem brighter. But it's a nice idea for peddling flashlights.