ZEISS offers a wide range of plastic sunglass lenses in a total of 74 colors. Graduated and bicolor tints are available in addition to single colors. Special tints for medical purposes are also included in the broad spectrum of Clarlet colors from ZEISS.
In addition to the standard range, Clarlet lenses with a refractive index of 1.5 can be tinted to match a supplied sample – in practically any color or absorption level imaginable. Any sample will do – whether it is a favorite pullover or lipstick, cycling gloves, or even a tinted lens not in the standard range of ZEISS colors.
Dip-coated plastic sunglass lenses display a uniform tint regardless of the prescription because the tint only penetrates the surface of the lens.
ZEISS has been tinting plastic lenses in dip baths since 1978.
Today, up to 7,000 plastic lenses are tinted in this way every day at Carl Zeiss’ plant in Aalen, Germany. This is approximately 40% of all plastic lenses delivered. The lenses are first inserted in special mounts, fixed in position and then dipped into the dye bath. During a maximum dwell time of 5 hours in the baths, the dye penetrates the lens surface to a depth of approx. 0.1 mm.
The temperature of the dye baths is always constant: for plastic lenses with an index of 1.5, for example, it is always 93°C. A magnetic stirrer in each of the baths ensures maximum homogeneity of the dye mixture.
The dip baths contain dye substances which are also used in the textile industry. Any shade or hue is possible using the primary colors red, yellow and blue. Special baths are used for Clarlet UV lenses. Graduated tints are obtained by using a special system developed by ZEISS. A computer controls the speed at which the lenses are gradually removed from the bath, resulting in a variation in the lens tint from bright to dark.
The tint is visually inspected on special tables with a white surface and illumination resembling daylight. All special medical filters and Clarlet UV lenses are subjected to an additional inspection test using a spectral photometer. In this case, it is not the color, but the absorption of certain wavelength ranges required for medical reasons which is of special importance. An exact photometric measurement of the lenses is therefore imperative.