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).
Instructions for altering headlights to a double-filament type and the principles of their operation.
| Identifier | ExFiles\Box 61a\1\ scan0329 | |
| Date | 1st December 1926 guessed | |
| Page -8- used. When I and IG lamps are altered to take double-filament bulbs, plain glass discs with frosted bulbs are used, but for IL lamps, ribbed glass discs with plain glass bulbs. Altering I, IG or IL headlights into double-filament type. Exchange the following: in the case of I and IG Headlights: 1. The spherical bulb to be exchanged for frosted double filament bulb, 2. The connection plate, 3. The glass disc (but only if headlight to be altered has ordinary ribbed lense); existing clear glass lenses may be retained, (For further particulars see dimensioned drawing A.M.L. 11B). in the case of IL Headlights: 1. The spherical bulb to be exchanged for clear glass double filament bulb, 2. The connection plate, 3. The ribbed glass disc. (For further particulars see dimensioned drawing A.M.L. 5B). In the case of headlights with auxiliary lamp (× 2) the tubular lamps are not affected by the alteration. In repeat orders, the type number of the double-filament lamp (see table on p. 7) and type number of main headlamp is to be indicated in addition to the information as to whether the bulbs are to be clear glass or frosted. Adjustment. The clamping flange must be made to fit the curvature of the wing, and the lamp fitted at an angle which will allow the beam of light of the main filament to meet the road at a distance of 650 to 820 feet in front of the car when loaded to approximately 100 to 130 lbs per seat and when the centre of the headlights is 32 to 40 inches above the ground. Page -3- The safety of driver, passengers, and other road users at night, depends on the quality of the headlights which should fulfil the following conditions: — (1) The light projected by the headlight must illuminate the road for the greatest possible distance so evenly and brightly that the driver, even when driving at very high speed, can clearly and immediately see any obstacle so as to avoid it or pull up. (2) The beam from the headlight must have a certain amount of diffusion so that the driver has no difficulty in seeing the whole width of the road and bends. Fig. 1. 7426 Headlight IL. 160×2/107 Fig. 2. Screen Anti-dazzle filament USDO main light filament contact for main light filament 726R contact for anti-dazzle filament Double-filament Bulb. (3) Drivers of oncoming vehicles and pedestrians must not be dazzled. The Bosch headlight with double filament bulb is designed to meet the above requirements, by using special bulbs with two filaments (Fig. 2) which give (a) a powerful main light and (b) an absolutely dazzle-free light with beam projected downwards. The main filament is in focus with the parabolic reflector. The anti-dazzle filament is in such a position that it is beyond the focus of the reflector and is a little above the axis of the focal position. Furthermore a metal cup is provided immediately below the filament in such a way that the beam is shielded from the lower half of the reflector. The whole of the light beam of this filament is, therefore, reflected from the upper | ||