Define 'Fresnel lens' and its purpose.

A Fresnel lens is distinguished by its unique design composed of concentric rings, which allows it to focus light effectively while being much thinner and lighter than a traditional lens of equivalent optical power. This innovative structure reduces the amount of material required, making it feasible to construct large lenses that can be used in various applications without the bulk and weight associated with standard lenses.

The purpose of a Fresnel lens is to capture and direct light efficiently. Due to its lightweight nature and the ability to focus light effectively, it is commonly used in applications such as lighthouses, projectors, and even some solar energy systems. The design maximizes the surface area while minimizing the volume, making it an essential tool in optical engineering where size and weight are crucial factors.