Commercial Applications of Blended Light

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    IN practical work, the term ‘blended light’ is used to describe the mixture of the light from the ordinary tungsten gas-filled lamps with that from mercury discharge lamps. A. H. Olsen contributes a paper to the Electrical Review for May 26 in which he discusses the blending of the light from these lamps. A gas-filled lamp depends on the light emitted by a tungsten filament; it therefore produces a continuous spectrum, red being prominent, but lacking in blue. The resultant colour is yellowish. A mercury lamp depends on the excitation of vapour and consequently emits a light with a broken spectrum, red rays being almost completely absent and blue being very pronounced. If the two light sources are mixed in the proper proportions, we get an approximation to white light. The effective application of this to shop lighting depends on the type of goods displayed; so no definite ratios of the two lights can be fixed and each installation is examined experimentally. In the case of drapers, furnishers and outfitters, where fabrics are displayed, the proportion of tungsten lumens to mercury lamp lumens is generally in the proportion of three to one. In practice, this means utilizing one 80-watt mercury lamp with two 200-watt tungsten lamps. When this is done, the colours of the fabrics appear much the same as with daylight. Black appears of a richer lustre, and red shades do not appear mauve as they do under mercury light. Although the consumption of electricity might have been expected to be less than if only tungsten lamps were used, it is found that owing to the amount of tungsten light required to blend with the mercury light, the consumption is much the same. In most of the main town shopping centres, blended light installations present a striking contrast to competitive windows in the same area, being much more prominent and displaying the goods more effectively.

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    Commercial Applications of Blended Light. Nature 143, 933–934 (1939) doi:10.1038/143933c0

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