1. Cox , N. T. , 1968 , The effect of dirt on vehicle headlamp performance . Road Research Laboratory , London . Report LR 240 .
2. Visible Distances and Safe Approach Speeds for Night Driving
3. ZACCHERINI , F. , 1971 , A summary of rosults and data concerning headlamp cleaning . Institute for Materials Testing , Stockholm . Report O-Ra-214 .