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Fres·nel lens

(frə-nĕl)

A thin optical lens consisting of concentric rings of segmental lenses and having a short focal length, used primarily in lighthouses, spotlights, overhead projectors, and the headlights of motor vehicles.

[AfterAugustin Jean Fresnel.]

(click for a larger image)

Fresnel lens

Prisms that make up a

Fresnel lens bend and

magnify light rays, creating

a single, concentrated beam

of light.

Indo-European & Semitic Roots Appendices

Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:

Indo-European Roots

Semitic Roots

The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.

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