VAPOUR LIGHTS

Evening Post, Volume CXXIII, Issue 51, 2 March 1937, Page 11

VAPOUR LIGHTS

THE TUNNEL TESTS

GREEN AND GOLDEN YELLOW

There are differences of opinion as to the greater effectiveness of the mercury vapour (greenish) and of the sodium discharge (golden yellow) lights which are being tested in the Mount Victoria tunnel, but there is no question at all of' their marked superiority over the standard incandescent lam£S which light the remainder of tiie tunnel. The new lights have improved visibility by at least 100 per cent, in the lengths in which they are installed, arid this is most noticeable when cyclists are met or overtaken. Moreover, the cost of maintaining these lights is, intensity for intenstiy, far below that of standard lights, for the current consumption is from one-fifth to one-third - that of' incandescent lamps. There are objections to these new types of lamps for ordinary lighting purposes, for the sodium discharge lamp in particular throws a monochromatic light under which it is hardly possible to distinguish one colour from another, since all colours . appear as shades between the typical golden yellow of the sodium flame and brown to black. Complexions are utterly ruined, and the most carefully prepared faceeyebrows, lipstick, cheek touches— has a cold touch. But on the highway the monochromatic light gains. The tunnel tests have been so successful from the motorists' point of view that it is probable that the council will be asked to carry the lighting right through, and, of course, the tests have a much wider interest than that, for highway lighting must receive attention in New Zealand as elsewhere as one means, and a very important one, of, reducing road "dangers. A road without a light is only half a road, it has been said, and it should have been added, a road 'with ineffective lighting is, for the motorist, worse than a road with none at all. There is a difficulty in introducing these modern highway lighting systems about waterfront roads at a port like Wellington, for the port authorities and thp Marine^ Department •• have clear ideas and rules about lights which may, under certain weather conditions, lead to possible confusion to shipping making up'the harbour, :and, it is understood, this aspect has been taken into serious account during discussions of a trial of highway lighting for the Hutt Road and Hutt Valley roads. ' ' • DOUBLY EFFICIENT. Not only do these vapour discharge lamps consume less power than incandescent lamps, but they are, intensity for intensity again, actually more efficient, for, because : of. the structure of the eye, sight is much more acute under monochromatic light of the blue-green and the yellow bands of the spectrum, the very colour ranges which are covered by the mercury ■ vapour lamp in one case and the sodium light in the other. The scientific argument behind that statement runs into many pages of technical detail, but that it is so is widely recognised.

With the development of lights which can throw light'in great intensity, and yet with the light source itself comparatively free from glare (having regard to the great candle power), a new conception of road illumination becomes possible, and this is> rather to illuminate the road surface so that any object will stand out in silhouette than to attempt to-light the object against a dark background. But the first aim of modern highway lighting is to illuminate the road'surface evenly, so that the eye does not have to adjust itself rapidly between the lighted areas immediately about or below the light and the dark areas—comparatively pitch dark—immediately beyond the lighted area.

Highway lighting has become almost a science in itself during the past two or three years. Wellington made the first step in New Zealand when the mercury lights were installed in Lambtpn Quay. Strictly speaking that may not be the place for them, for they do interfere with good looks, though not nearly to the same horrific degree that the sodium lights do. but Wellington people are pretty well used to them now, and the City Council is very well pleased with the economy of operation and the greatly improved lighting of the road surface. The new type of highway lighting has been installed on a fairly big scale on an Auckland highway and it can be taken as certain enough that .more and more attention will be paid to it on many of the heavy traffic^ roads about the main cities.