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).
Investigation into the use of frosted versus clear glass bulbs in R.R. & Bentley headlamps.
| Identifier | ExFiles\Box 61a\2\ scan0242 | |
| Date | 9th March 1934 | |
| 6mb To Sg.{Arthur F. Sidgreaves - MD} C. to Cor. C. to C. C. to R.{Sir Henry Royce} C. to Hn.{F. C. Honeyman - Retail orders} C. to Hy.{Tom Haldenby - Plant Engineer} Re/Wst.2/KW.9.3.34. R.R. & BENTLEY HEADLAMPS. At the request of C. we arranged to visit Messrs. Lucas' Works on Tuesday last, to investigate the reason why Messrs. Lucas recommended frosted bulbs instead of clear glass bulbs. A memo, received from C., reference C1/L.31.1.34, referred to the fact that when clear glass bulbs were fitted to a car in preference to frosted glass, considerable improvement with regard to illumination was achieved. Mr. Neill of Messrs. Lucas agreed that a certain amount of extra light could be obtained with the use of clear bulbs, but with the addition of high spots in the beam. The adoption of frosted bulbs eliminates such high spots which are caused by inaccuracies in the reflector and also due to the fact that the bulb filament has appreciable length and therefore does not always throw out light exactly from the focal point of the reflector. There was no doubt about this when we were shown the demonstration in their dark room. We discovered, however, that some bulbs they were sending out were rather heavily frosted, and it is quite possible that on a number of bulbs supplied to us the frosting has been overdone. Messrs. Lucas realise this and have given us a guarantee that on further supplies of lamps they will ensure that the frosting is only carried out slightly, just sufficient to even out the beam. The frosting on these bulbs is carried out by acid etching the glass, and could therefore be done quite easily to any desirable amount. When the bulbs are heavily frosted the available light is certainly impaired. | ||