The property of light used in lenses is **refraction**.
### Definition:
**Refraction** is the bending of light as it passes from one transparent medium to another with a different density. This change in speed causes the light to change direction.
How Refraction Works in Lenses:
When light enters a lens, which is typically made of glass or plastic, it slows down if the lens material is denser than the air. This slowing down causes the light rays to bend at the interface between air and lens material. The shape of the lens (convex or concave) then directs the light rays to converge or diverge, forming an image.
- **Convex lenses** (thicker at the center than at the edges) cause parallel light rays to converge to a focal point.
- **Concave lenses** (thinner at the center than at the edges) cause parallel light rays to diverge as if they were emanating from a focal point behind the lens.
Refraction is fundamental in the functioning of lenses in various optical devices like eyeglasses, cameras, microscopes, and telescopes.