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).
Letter from the American branch discussing lamp bulb specifications and headlamp technology.
| Identifier | ExFiles\Box 166\4\ img107 | |
| Date | 16th March 1931 | |
| 7.J.A. X6089 ROLLS-ROYCE OF AMERICA, INC. SPRINGFIELD, MASS. Btn-3 March 16, 1931. RECEIVED 1931 MAR 27 POST OFFICE DERBY 27 MAR 31 RECEIVED Rolls Royce, Ltd., Derby, England. Attention of Mr. E.{Mr Elliott - Chief Engineer} F.{Mr Friese} Clark. Dear Mr. Clark: We thank you for your letter of the 21st of February and enclosed list of lamp bulbs used on 25 HP. and PII. We are not able to tell you yet the exact lamps which we shall use, but will have to shop around a little till we find the most suitable. Commenting on your list, we would say: 1. All lamps we use at present are of the Westinghouse Mazda type. They are specified by volts and candle power, where-as yours apparently are specified by volts and watts. How-ever, the conversion is fairly simple. 2. Headlamps. Standard voltages are 6-8 and 12-16. Candle-power is almost universally controlled by law, but varies a little in different states - some specifying exactly 21 and others permitting 32 candlepower. Our practice is to use a two filament bulb, with the headlamp constructed so that one filament is in focus with the reflector and the other is approximately .140 higher. On meeting an approach-ing car the custom is to switch over from the main focussed filament to the secondary higher filament which throws the rays down onto the road. This is effected by means of the dimming switch. Our present standard bulb has 21 and 32 candlepower filaments, fitted normally with the 32 candle-power filament in focus, with the intention that when used mainly in those states where 32 candlepower is illegal, the bulb should be inverted using the 21 candlepower in focus. - Continued - | ||