This is so good. I thought I knew what he meant here but did a little digging to verify. This is from American Voices of World War I: Primary Source Documents, 1917-1920:

Fresnel lenses are composed of a series of concentric grooves etched into one side of a sheet of plastic. Fresnel lenses are unlike typical spherical or aspherical optical lenses. The grooves of Fresnel Lenses act as individual refracting surfaces, making these lenses ideal for solar concentration, solar cell heat collection, overhead projection, and non-imaging light focusing applications. Monica Rainey, Optical Engineer, explains the advantages, disadvantages, and applications of these unique lenses. To learn more, read our Advantages of Fresnel Lenses application note.

L'entreprise Edmund Optics GmbH en Allemagne agit comme un mandataire d'Edmund Optics Ltd au Royaume-Uni. Le titulaire du contrat est Edmund Optics Ltd au Royaume-Uni.