Some Polarised Headlight Systems

Abstract

This is the second of two papers dealing with polarised headlight systems. The first paper discussed the relative merits of commercially available filters for polarising headlights. The present paper discusses the widely differing proposals that have been put forward in America and Germany for the use of polarised headlights, and records the results of tests made with an alternative system. The discussion and tests are concerned only with the benefits to drivers of vehicles. The consequences to pedal cyclists and pedestrians are not discussed in this paper.

Any polarising device fitted to a headlamp will reduce the light available for seeing. The American system overcomes this handicap by increasing the power of the polarised headlights, so that the user always sees at least as well as with the driving beam of conventional headlights; the German system on the other hand uses a polarised beam which is no more glaring to face without a visor than existing German meeting beams. Neither system would be easy to introduce, because initially the benefits to the user would, for different reasons, be limited to the occasional meeting with another user.

Polarisation of existing driving beams might provide a system which operated between these two extremes, and might enable the user to see objects in his own beam at greater distances than usual even when meeting normal beams. Driver-appreciation tests with the system, however, suggest that it does not illuminate the road near the vehicle well enough to inspire confidence, and that the loss in silhouette seeing is a real disadvantage. Preliminary experiments suggest that both criticisms might be overcome with an in-part polarised system in which the near view is illuminated by unpolarised light and the distant view by polarised light.