The most common studio lighting instruments are "Fresnels" (Pronounced Freh-NELL. Never say Frez-NELL.)

Fresnels have two important features. First, they have a lens on the front of the instrument. This allows light to be focused into a narrow beam. It's is an important feature in television or film production. For example, in a given scene, it might be preferable to have the star be a little brighter than the background actors—so she 'pops' out at the audience. A fresnel can direct a narrow beam onto the star's face. And because the lens on the fresnel provides such a tightly focused beam, no light spills onto the secondary actors in the background.