THE MITIGATION OF HEADLIGHT DAZZLE.
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The President of the C.M.U.A. Contends that the Evil of Glare can be Reduced by the Employment of Tinted Bulbs at a Small Extra Cost.
HAVING always in view the interests of the drivers of commercial motors and their safety and that of their vehicles and Wads on the road at night-time, the President of the National Council of the C.M.U.A., Mr. E. S. Shrstpnell-Smith, C.B.E., M.lnst.T., has for some time been closely studying the question of headlight glare. He studied the devices produced for demonstration at the trial promoted in Richmond Park last winter by the RA.C. 'and later wrote to The Times on the subject. The National Council thereupon requested him to stimulate investigations into various methods of securing the desired mitigation of dazzle, and lines of research were 'accordingly laid down. On Wednesday last, at the Savoy Hotel, he gave a lecture illustrated by a demonstration of suitable devices in which he showed that important results have been achieved in the six months that have elapsed.
He said that the limiting conditions of this research, which it will be realized excluded every device and fitting then on the market (in February last), were fixed as under in order to keep down the cost to all concerned :— (1) No existing standards in the manufaciure of lamps, fittings or electric bulbs Were to be altered. (2)• The driving light was not to be reduced by more than one-fifth as between untreated bulb and the same bulb after tinting and anyallied or consequential processing. (3) There was to he no switching off and on and no other call for personal attention from the driver. (4) The in clusive.extra charge per headlamp for conversion was not to exceed half-a-crown to the retail purchaser: It is interesting to record that the Home Office and the Ministry of Transport have shown active and helpful interest in all that has been done. . "It is desirable to recall that the Government Committee which last reported on this matter, of which Committee," said the lecturer, "I was a member, recommended the provision of sufficient forward illumination to pick up, under specified conditions, a standard disc, corresponding to a pedestrian inconspicuously dressed, at a minimum of 150 ft. and a maximum of 300 ft. The indicated incan distance of 225 ft. provides ample margin for. pulling up a motorcar which is travelling at even so high a speed as 40 miles an hour, on the esEumption that it has brakes on only two of its wheels . and after allowing more than the average lag of threequarters of a second for effective impulses between the eyes, brain and limbs of its driver. .
" Our first duty has been towards -owners and drivers of motor vehicles, and, above all, towards the drivers of motor omnibuses and certain classes •Of goods vehicles whose work requires that they shall be out on the roads during many successive hours of darkness. We have also sought to pay adequate regard to the men, women and children who are literally in the
street and therefore below the average eye-level of the motor driver when in his seat.
"My own road trials in England and Scotland have been supidemented very largely by an uninterrupted series of comparative tests, extending over many months, in regular omnibus service, by the Aldershot and District Traction Co., Ltd. These conclusions are:— " (1) That no one tint or method of treatment holds the field exclusively. (2) That essential modification of all British automobile standard bulbs can be carried out at small cost (a) by admixture of pigments in the pot of molten glass before blowing, or (b) by dipping or spraying any of these standard uncoloured bulbs after the usual course of manufacture has been completed. (3) That yellow or cobalt blue gives the best results in filtering out the offending red rays, and that cobalt blue properly applied yields the nearest approach to true daylight or white light. (4) That clear yellow or blue glass only eliminates dazzle attributable to light radiated from a white-hot filament, and that a slight degree of opacity on or in the wall of the bulb is required to mitigate the dazzle attributable to the reflected. image of such, white-hot filament. (5) That dazzle can be mitigated to a noteworthy extent by treatment of half areas of the surface of any headlamp bulb, but that still better results are to be expected from treatment of the entire bulb. ((3) That incorporation of a pigment in eortjunction with the requisite degree of opacity in the wall of the bulb during Its primary Manufacture may ultimately be found preferable to any method of dipping or spraying. (7) That where treatment of a bulb is limited to its top half, the best results can be obtained only when the line filament is mounted behind the focus of the parabolic reflector. (8) That the Association's terms of reference can be met in all respects, and that in the ease of one make of treated bulb which has given highly promising results under test (the Osram half-sprayed yellow) the additional retail charge per headlamp is only ninepence. (8) That the driving light resulting from the use in headlamps of standard B.A.S. bulbs tinted and treated by either of the methods indicated possesses the additional merit of penetrating fog and mist to a helpful extent.
" Finally, I wish to express my personal gratification and that of the Association concerning the interest which the Home Seeretary has shown in this work. Sir William Jo,vnson-Hicks, I feel, appreciates the public importance of such efforts and the general benefits which must flow from Ehem.The substitution of tinted and treated translucent bulbs for colourless transparent ones will, no doubt, appeal to him as offering a quick and ready method of mitigating dazzle as well as a choice in detail."