This type of filters has been used in competitions under low contrast conditions with significant improvements in terms of performances. Tristimulus curves modified by effect of a high contrast filter. For a better comprehension of the benefits in terms of improvement of the chromatic contrast, one can examine the relative coefficients of transmittance of the colours Blue, Red, Green and Yellow, as defined by the European Standard EN 1836. These coefficients were defined by the standard to provide an indication of the degree of attenuation of road sign colours as compared to the background by effect of the filter used. Factors smaller than one indicate an attenuation of specific colour.
Greater values indicate enhancement of the specific colour and, consequently, better visibility.
Normally, a grey filter has factors equal or close to one, while in the other cases the increase of any of the factors is compensated by an equivalent attenuation of others. In the case of high contrast filters which use the principle described in this paragraph, a generalised increase of the relative transmittance factors is obtained instead, without affecting any of them. The message I have to share with you is an important one. It describes what I believe to be the greatest discovery of the 20th century affecting visual health. It sets the stage for a new era in the next century.