Lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam.
Figure 2.4.1: Two basic types of lenses – converging and diverging.
A simple lens consists of a single optical element. A compound lens is an array of simple lenses (elements) with a common axis. The use of multiple elements allows more optical aberrations to be corrected than it is possible with a single element. Lenses are typically made from glass or transparent plastic.
Figure 2.4.2: Different types of lenses used with LED light sources.