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).
Different methods of headlamp dipping, specifically comparing a three-lamp system with bifocal dipping using a two-filament bulb.
| Identifier | WestWitteringFiles\T\2July1928-December1928\ Scan085 | |
| Date | 1st September 1928 | |
| HS.{Lord Ernest Hives - Chair} FROM DA{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork} ORIGINAL DA{Bernard Day - Chassis Design}/EV{Ivan Evernden - coachwork}1/M3.9.28. Copy to R.{Sir Henry Royce} BJ. re. BIFOCAL DIPPING. X4477 We understand from R.{Sir Henry Royce}, and also from CWB., that the scheme whereby one has a third headlamp mounted centrally between the main ones, which is permanently dipped and twisted and operated in conjunction with a two way switch, is a very effective method of achieving what our mechanical dippers do, namely, of providing a straight ahead beam, or a dipped and twisted beam. Its sole disadvantage appears to lie in the fact that the angle of dip cannot be graduated from the driving seat. It is however much simpler to fit than a lot of mechanism which is required to dip the main lamps. We would like to try the system, which we understand is very popular in the States, known as bifocal dipping. The headlamp bulb has in it a main filament which is at the focus of the reflector, and another filament displaced above and to one side, so as to cast a beam downwards towards the near side. These filaments are operated by means of a two way switch. This scheme appears to give us our dipping lamps with no mechanically moving parts. What we would like to know is can we get bifocal bulbs in this country for 12 V.{VIENNA} lighting sets, or are there any firms thinking of taking the matter up. For test purposes we might get a complete set of lamps and bulbs from the States. Would Derby kindly go into this matter for us. DA{Bernard Day - Chassis Design}/EV.{Ivan Evernden - coachwork} | ||