It is correct and usable in written English.
It can be used to refer to lenses, such as those on a pair of sunglasses, that are tinted in such a way as to reduce the brightness of light entering the eyes. For example, "The trendy sunglasses I bought have gradient lenses to protect my eyes from the sun."
I had the frames for reading and asked to have them made with black gradient lenses.
Also popular are gradient lenses that change from a darker to lighter color, opalescent-colored glass, brown lenses, retro-inspired designs and rimless styles.
In contrast to the '70s originals, which made people seem aloof or anonymous, contemporary variations often feature gradient lenses that are tinted on top and clear below — a more approachable look.
Two measurements, focal length and radius of curvature of the lens, can be used to distinguish gradient lenses from homogeneous lenses.
For example, gradient lenses have a much shorter focal length than homogeneous lenses with the same central refractive index, and the radius of curvature of a gradient lens is about 2.5 lens radii, compared with 4 radii for a homogeneous lens.
Tortoise-shell frames by Salvatore Ferragamo and Fendi soften the edges of the face through the use of color and gradient lenses.
Furthermore, a newly designed radial refractive gradient lens (RRG lens) that induces increasing myopia in all radial directions from the center was tested.
Driscoll, T; Basov, DN; Starr, AF; Rye, PM; Nemat-Nasser, Schurigrig, D; Smith, DR, Free-space microwave focusing by a negative-index gradient lens, Applied Physics Letters, vol. 88 no. 8 (March, 2006), pp. 081101-081101, AIP Publishing [doi] [abs].
Driscoll, T; Basov, DN; Rye, PM; Nemat-Nasser, Schurigrig, D; Smith, DR, Free space microwave focusing by a negative-index gradient lens, Smart Structures and Materials 2005: Active Materials: Behavior and Mechanics, vol. 6320 no. 8 (November, 2006) [doi] [abs].
The diameters of 50 haphazardly picked beads (50 uncoated, 50 single coated and 50 double coated beads) were determined by means of an eyepiece micrometer on an optical microscope (Nikon-Model Alphaphot-2 YS2-T. Jatan) at a magnification of 10× (magnification factor for each unit of gradient lens was 10.89 at magnification of 10×).
Double-gradient lenses, which are dark at the top and bottom and lighter in the center, absorb reflected light that comes from below and above; they are also good for boating.
