Abstract
Progress in the efficiency and colour quality of discharge lamps is reviewed. Spectral band histograms give details of the distribution of radiation in sixteen bands covering the near ultraviolet and visible regions. Radiated power in each band combined with the appropriate factor for luminous efficiency of radiation enables the luminous efficiency of each lamp type to be determined. Improvements in the efficiency and colour of discharge lamps is illustrated by similar histograms for high- and low-pressure mercury vapour lamps and experimental high-pressure sodium and mercury iodide discharges.
Colour-rendering improvements are assessed by comparing the radiant power histograms with those of natural sunlight and skylight: modern fluorescent lamps duplicate these distributions sufficiently closely in both the visible and near ultra-violet regions to make it practicable to bring lighting of natural quality indoors. The introduction of balanced colour into lighting greatly increases the number of contrasts available. The trend of interior lighting towards the natural standards of daylight and sunlight is considered.
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