Abstract
To express the colour-rendering properties of light sources, a band system of presenting the spectral energy distribution has been used. The best known example of this is Bouma's eight-band system. In this paper Bouma's method of treating the problem is criticised, and the uses and drawbacks of band systems discussed. The next stage of condensation of information on spectral energy distribution leads to single figures of merit to measure colour-rendering properties. Related to this is the present proposal for expressing a single feature of colour-rendering behaviour of fluorescent lamps, namely the red-rendering efficiency, as an index which will distinguish easily between lamps of the “high efficiency” and “high fidelity” types. It is based on the ratio of energy output at two selected wave-lengths, compared with the ratio for a black body or “Planckian radiator” of near or identical colour appearance. Various methods of determining the index are discussed, varying from a calculation based on spectrophotometry to a direct meter measurement. Data are given for a wide selection of lamps.
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