Study of light scattering on a soda lime glass eroded by sandblasting

In Saharan areas of Algeria, sandstorms can damage vehicles windshields inducing incidental light diffusion that affects the driver's visibility. Vehicles technical controllers find some difficulties with damaged windshields. The control being made visually with the naked eye, it is therefore difficult to judge when a damaged windshield is no more valid to use. In this context, we studied the influence of the surface state of a soda lime glass on the scattering of a white light. The varying parameters considered are the projected sand mass, the opening of the light beam and the distance sample-receptor. By increasing the projected sand mass up to 200 g, the optical transmission falls from 91.6 to 13% and the roughness increases from 0.035 up to 2.27 μm and then tends toward a constant level. For the as-received state, the image obtained using a CCD camera presents a net boundary and the transmission profile shows a saturation plateau. By damaging the surface, the image boundary deforms and becomes diffuse. For the highly damaged states, the image become completely blurred and the transmission profile disappears. The variation of the transmission according to roughness shows an inflection point at T = 73% and Ra = 1.5 μm. This point seems to separate two domains: a transparent field (Ra < 1.5 μm) and a blur field (Ra > 1.5 μm). The visibility limit obtained in our tests conditions is estimated at about 73%.