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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).
Report from Joseph Lucas Limited discussing the performance of various headlamp bulbs and systems.

Identifier  ExFiles\Box 61a\2\  scan0411
Date  30th November 1934
  
CONTINUATION

JOSEPH LUCAS LIMITED

PAGE DATE

Messrs.Rolls-Royce Ltd.,

2. 30.11.34.

spreading the beam slightly and adding a certain amount of side light by means of a spreading lens on the tripod after the manner of our Sports head-lamp with which you are familiar.

The lighting in the dipped position we found disappointing. The drop in intensity in changing over from the normal position was much too great, except under most favourable atmospheric and road conditions and one would never give credit to the fact that approximately 96 watts were being expended. Certainly one bulb of this rating in a split-reflector lamp would give altogether superior results and the writer is having some experimental bulbs made up in case you may be interested to try comparative tests with the two systems.

As you know, we investigated the combination of the Lucas Graves Bulb with our P.100 lamps some years ago, using similarly rated bulbs to the present ones and what we see now only confirms our previous opinion that for this country the proposition is not an attractive one and in changing over to this system from your present double dippers in particular, you would receive complaints of lack of adequate illumination in the dipped position. This is not surprising when it is realised that whereas with the standard lamps a total wattage of 120 is projected on to a reduced area of road in the dipped position with a consequent increase in intensity as the square of the reduction; with the Graves Bulb the effective wattage from both bulbs totals only 48, the beam at the same time being spread over a larger area.

We admit, of course, that the relief from glare in the dipped position is greater with the Lucas Graves Bulb, but equally good results would be obtained with a correctly designed Centre Lamp, which moreover, would carry a greater psychological effect both to the user of the car and to oncoming traffic.

We look forward with interest to hearing the results of your tests with these lamps and the writer

Continued......
  
  


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