The optical properties of the Lexan® film have an essential importance for numerous graphical and packaging applications. Lexan® film is one of the clearest films on the market because of its high translucency and low turbidity.

Turbidity

Turbidity is a measure for the quantity of light in per cent which is lost by a light beam because of the scattering in the material. Turbidity affects the clear identification of objects behind the film and leads to a blunt effect of the black-sided printing colours. The low turbidity of polished Lexan® films ensures a maximum of clear transparency and colour fidelity.

Yellowness

The yellowness is the variance of a film to the colourlessness (water clarity) measured at simulated daylight in comparison to a white target colour (Magnesium oxide). Low yellowness means low variance to the white and back-sided pastel colours. Lexan® films are available in a special quality with controlled yellowness. Please ask your regional film supplier for more information.

Translucency

Diagram 1 shows that most of the Lexan® films let 90% of the visible light pass but they act against UV light nearly opaque. This protects background graphics, packaged articles and even the film itself against defects from UV solarisation. For longer outdoor weathering with direct solar radiation, UV stable films should be used because otherwise the surface may chalk.

Refraction index

The optical refraction index of transparent materials is determined on the basis of the chance of direction of the light beam. The light beam changes its direction on its way through the sample. The index results of the quotient of the sine value of the entrance and exit angle (a and b). The angles refer to the perpendicular line.

Picture 1

Optical properties of the Lexan films

Diffusion of the Lexan films

Diffusion is a measure for the loss of vertical translucence because of scattering, according to DIN 5036. Usually this test method is used if the scattering is desired or if the turbidity values become unreliable (<35%). With the help of structures and special filter systems it is possible to optimise the diffusion of the films systematically.

Chart 6: Diffusion of Lexan® film

Diffusion of Lexan® film

Chart 7: Halfpower angle of the Lexan® films

Halfpower angle of the Lexan® films