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).
The limitations of bifocal bulbs and an overview of alternative headlamp solutions, including the P.100 model with a dipped beam.
| Identifier | ExFiles\Box 61a\1\ scan0387 | |
| Date | 30th October 1928 guessed | |
| Contd. -2- distortion of the beam as the filament moves away from the axis of the reflector. We have made many experiments with special bulbs made to our specification to see if the standard arrangement could not be improved upon, but the bifocal system is distinctly one of compromise, and it is not practicable to have the offset filament very much further offset without entirely destroying the beam. You will gather from these remarks that we consider that the bifocal bulb to be a rather poor palliative to the dazzle problem, and not worth consideration in conjunction with our P.100 headlamp. In addition to this, the reflector of the P.100 which as you know combines a glass mirror and a parabolic reflector, does not lend itself to the system under discussion quite so well as an ordinary parabolic reflector, which is another reason for our doubt of the advisability of your pursuing the matter further. You may have noticed at our Stand at the Motor Show, an improved model P.100 headlamp which we have introduced to meet the request for a dipped beam. This lamp incorporates an auxiliary bulb behind a small lens in the top half of the reflector which, when in operation, throws a flat dipped beam which is most effective when driving through towns and meeting oncoming traffic. By moving the auxiliary bulb up and down in its holder, it is possible to settle on an angle of dip between wide limits to suit individual requirements. Once decided upon however, the angle of dip cannot be altered without readjusting the auxiliary bulb. The change [crossed out] over from the main bulb to the auxiliary is effected by a small switch placed on the steering column, or the dashboard whichever is the more convenient. We have had some encouraging comments passed on this lamp by various users, but it is yet in the experimental stage, in so far that we have not finally decided to go ahead with production. If you will refer to the correspondence between your West WitteringHenry Royce's home town house and Mr. Oliver Lucas, you will see that we are also considering a mechanically operated dipping reflector for the P.100 headlamp, and it is for this reason that we are not yet pushing the double bulb type. We trust these remarks have been clear to you, but if this should not be the case, or if we can give you the benefit of our experience on any similar problem, we shall be only too glad if you will advise us of the fact. Yours faithfully, | ||