Journal of electricity, power, and gas . SPACING OF LIGHT-UNITS. BY THOMAS W. ROLPH. (In this article is given a method for determiningthe proper spacing of light-units when their photo-metric curves are available. It will be found of greatvalue to the practicing illuminating engineer.—TheEditors.) The degree of uniformity of illumination obtainedin any lighting installation depends upon the spacingof the light-units. When several units are used tolight an area it is desirable to arrange them in the formof squares or rectangles as nearly square as ratio of the length of one side o
Journal of electricity, power, and gas . SPACING OF LIGHT-UNITS. BY THOMAS W. ROLPH. (In this article is given a method for determiningthe proper spacing of light-units when their photo-metric curves are available. It will be found of greatvalue to the practicing illuminating engineer.—TheEditors.) The degree of uniformity of illumination obtainedin any lighting installation depends upon the spacingof the light-units. When several units are used tolight an area it is desirable to arrange them in the formof squares or rectangles as nearly square as ratio of the length of one side of the square to theheight of the light-unit above the horizontal plane onwhich illumination is desired, is the important factorin determining uniformity of illumination. This ratio. Fig. 1. is usually referred to as k, and is called the spacingconstant. With any given installation of light unitsif the distance apart and the height are varied in such amanner that k remains constant, the uniformity ofillumination will not be affected, although the averageintensity of illumination will vary. For any value of k there is a minimum photometriccurve for uniform illumination. This curve will giveat that particular spacing the highest illumination ef-ficency consistent with uniformity of illumination. Thefamiliar extensive, intensive and focusing reflectors aredesigned to approximate such curves. The values ofk for the extensive, intensive and focusing curves arerespectively 2, 1% and %. In other words, if it isdesired to mount the light-units at k = 2 or the heightone-half the distance apart, the most efficient curvegiving uniform illumination is the extensive curve. Asa general rule, spacing light-units closer together orhigher than their correct k-value calls for, stil
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