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The Appraisement of Lighting

    Naturevolume 140pages763764 (1937) | Download Citation



    FOR the twenty-second Guthrie Lecture before the Physical Society on October 22, Dr. C. C. Paterson discussed "the Appraisement of Lighting". Dr. Paterson pointed out that as techniques have become available during the past thirty years, the art of appraising lighting has changed and advanced greatly. Like so many other subjects, however, that of lighting and seeing has been and is held in check by the inevitable tendency of those who practise it to define it at any epoch in terms of the quantities which they understand. Whereas research can stretch out where it pleases it is difficult for a practical art to advance faster than the established techniques for appraising its merits. The earliest standard ever adopted, specifying a candle of a certain weight in a lantern, is one which has many advantages and which under a changed form is still probably the most widely adopted. The most easily measured characteristic of a light source is luminous intensity, but a measure which is of more value in estimating the aid to seeing is that of luminous flux. With the advent of differently coloured light sources difficulties of such measurements have grown. The adoption of an internationally accepted relative luminosity curve for the average human eye has brought the measurement of intensity of illumination to a high state of accuracy for sources with continuous spectra. The use of the photocell has added to speed and repetitive accuracy, but not to absolute accuracy.

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