From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Summary of experiments on the effectiveness of coloured headlamp beams and filters in foggy conditions.
| Identifier | ExFiles\Box 61a\2\ scan0388 | |
| Date | 1st September 1934 | |
| Copy. I.A.E. RESEARCH AND STANDARDISATION COMMITTEE. Research Department, 5, Bolton Road, Chiswick, W.4. No.7251. Class 476, 32. Deptember 1934. Motor Car Headlamps in Fog. A.H. Stuart. Engineering, Aug. 3.1934. p.107. The author has carried out experiments to ascertain whether any benefit can be obtained by the use of coloured beams and, if so, what colour would give the maximum benefit. If a white beam of light is passed through a fog and is then examined in a spectrophotometer it is found that the absorption of wave lengths of 5,200 to 4,000 A.U. is so great as almost to amount to extinction. Scattered light is not really adsorbed but forms a halo or "black glare" which has a blinding effect upon the driver. The most which can be expected from the use of a filter is the elimination of this "black glare" and it was considered that this might be accomplished if a filter could be produced which would be almost completely transparent to light of wave lengths between 5,400 and 6,500 A.U. and as opaque as possible to wave lengths of 5,200 A.U. and shorter. A glass, called 'Nebulite' which is stated to have these characteristics has been produced by Messrs. Pilkington Bros.Ltd., and is marketed by the London Motor Accessories Co. Spectrograms show the effect of 'Nebulite' and of other filters and indicate that none of the glasses hitherto used has been capab le of giving satisfactory all-round results. It is shown that screens of apparently the same colour may give widely differing results. The small loss of light with a 'Nebulite' filter is rendered negligible by the great advantage of the hardened contrast which is obtained. C.G.W. | ||