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 Joseph Lucas Limited regarding the characteristics and performance of bifocal headlamp bulbs.
| Identifier | ExFiles\Box 61a\1\ scan0392 | |
| Date | 30th October 1928 | |
| CONTRACTORS TO THE ADMIRALTY, WAR OFFICE, AIR MINISTRY, INDIA OFFICE, G.P.O. AND LEADING RAILWAYS. Codes: ABC 5TH & 6TH EDITS & BENTLEYS TRADE MARK JOSEPH LUCAS LIMITED GREAT KING STREET BIRMINGHAM TELEPHONES: NORTHERN 2201 (10 LINES) TELEGRAMS & CABLES: "LUCAS, BIRMINGHAM" "KING OF THE ROAD" LAMPS, HORNS, "CYCLEALITIES", "MOTOR-CYCLEALITIES", "MOTORALITIES", MAGNETOS, BATTERIES, ELECTRIC LIGHTING & STARTING SYSTEMS SERVICE DEPOTS BELFAST, 3-5, CALVIN ST.{Capt. P. R. Strong} BIRMINGHAM, GREAT HAMPTON ST BRISTOL, 25, TEMPLE STREET. COVENTRY, PRIORY STREET. DUBLIN, TAYLOR BROS. 41, MIDDLE ABBEY ST.{Capt. P. R. Strong} GLASGOW, 227/229 ST GEORGE'S RD LEEDS, 64, ROSEVILLE ROAD. LONDON, DORDRECHT RD ACTON VALE, W.3. LONDON, 759, HIGH ROAD, LEYTON, E.10. LONDON, 155, MERTON RD WANDSWORTH, S.W.18. MANCHESTER, TALBOT RD STRETFORD. NEWCASTLE-ON-TYNE, 64-66 ST MARY'S PLACE. WHOLESALE DEPOTS BELFAST, 3-5, CALVIN STREET. BRISTOL, 25, TEMPLE STREET. DUBLIN, TAYLOR BROS. 41, MIDDLE ABBEY STREET. GLASGOW, 227-229 ST.{Capt. P. R. Strong} GEORGE'S ROAD. LEEDS, 64, ROSEVILLE ROAD. LONDON, 224, SHAFTESBURY AVENUE, W.C.2. MANCHESTER, 291-293, DEANSGATE. NEWCASTLE-ON-TYNE, 64-66, ST MARY'S PLACE. WHEN REPLYING PLEASE REFER TO RLN/FEA. Messrs. Rolls Royce Ltd., DERBY. 30th October, 1928. Dear Sirs, Re Bifocal Bulbs EFC8/T. We thank you for your letter of the 24th inst., with reference to the above, and we are glad to be able to give you our experiences with this type of bulb. As you probably know, the majority of American headlamps employ some sort of dipped beam arrangement, and this effect is achieved by using a bifocal type of bulb, and a special form of headlamp glass. The bulb is provided with two filaments, one at the focus of the reflector and the other slightly above it. To achieve any marked displacement of the beam it is necessary that the source of light i.e. the filament should be as small as possible, and also that the bulb should be correctly focussed. This naturally results in a pencil of light quite unsuitable as a driving light, and it is customary to spread this beam in a lateral direction by a moulded front glass comprising in its most elementary form a series of vertical curved faces. You will have noticed the wonderful | ||