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 to Lucas Electrical Co. Ltd. about the benefits and operation of double filament headlamp bulbs.
| Identifier | ExFiles\Box 61a\1\ scan0238 | |
| Date | 23th August 1926 | |
| X1357 Hs{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}3/T. 23rd August, 1926. Messrs. The Lucas Elec. Co.Ltd., Well Street, Birmingham. X.1369 X.1357 X.4291 Dear Sirs, We have received the following letter from America with reference to a double filament type bulb which they are fitting in the lamps over there. "We wish to advise you that we have recently found a distinct benefit from fitting our headlamps with "double filament" bulbs. These carry two filaments set .140" apart, and are mounted in the parabolic reflector .070" above center. Both filaments are of the same power (21 c.p.) When the lighting switch is on the "Head" position the lower filament (which is on the axis of the reflector) is lighted and road illumination is normal. When the switch is on the "dim" or "auxiliary" position, only the upper filament is illuminated, which is .140" above the axis of the parabola. Under these conditions the bright illumination strikes the road about 100 feet ahead of the car, shews up the ditches excellently, and does not dazzle approaching cars. The action of "dimming" therefore gives a better illumination in the glare of approaching headlights, than the full "head" position, and becomes a matter of self-protection rather than courtesy. " We should like to know whether you have carried out any experiments in this direction and if so whether you are in a position to supply us with something which we can try out. Contd. | ||