ZEISS offers a wide range of plastic sunglass lenses with a total of 74 colours. Graduated and bicolour tints are available in addition to single colours. Special tints for medical purposes are also included in the broad spectrum of Clarlet colours from ZEISS.
In addition to the standard range, Clarlet lenses with the refractive index 1.5 can be tinted to match a supplied sample – in practically any colour or absorption level imaginable. Any sample will do – whether it is a favourite pullover or lipstick, cycling gloves, or even a tinted lens not contained in the standard range of ZEISS colours.
Dip-coated plastic sunglass lenses display a uniform tint irrespective of the prescription, as the tint penetrates only 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 in the Aalen plant of Carl Zeiss in Germany every day. 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 the index 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 colours 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 colour, 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.