Journal of electricity, power, and gas . curvesshown in Figs. 1 and 2. What might be termed freakcurves, such as shown in Fig. 3, cannot be spaced togive uniform illumination efficiently. They are unde-sirable for general illumination. To determine the best k-value for curves as shownin Figs. 1 and 2, any slight irregularities should befirst eliminated and the dotted line curves shown in thefigures should be used. These dotted line curves arefor practical purposes the same as the solid line testcurves. After making this revision in the curve, itshould be compared with the critical angle curve
Journal of electricity, power, and gas . curvesshown in Figs. 1 and 2. What might be termed freakcurves, such as shown in Fig. 3, cannot be spaced togive uniform illumination efficiently. They are unde-sirable for general illumination. To determine the best k-value for curves as shownin Figs. 1 and 2, any slight irregularities should befirst eliminated and the dotted line curves shown in thefigures should be used. These dotted line curves arefor practical purposes the same as the solid line testcurves. After making this revision in the curve, itshould be compared with the critical angle curve Tabic I. Critical Angle. k. Critical Angle. k. 10° .35 31° 11° ,39 32° 12° .43 33° 13° .46 34° 14° .50 35° 15° .54 36° 16° .57 37° 17° .61 38° 18° .65 39° 19° .69 40° 20° .73 41° 21° .77 42° 22° ,81 43° 23° .85 44° 24° .89 45° 25° .93 46° 26° ,98 47° 27° 48° 28° 49° 29° 50° 30° Fig. 4. shown in Fig. 4. This curve is derived from the proto-type or original extensive, intensive and The photometric curve (dotted line) shouldbe plotted to the scale 100 units downward; i. e., allthe values should be increased or decreased in the pro-portion which will make the downward intensity this curve with the critical angle curve theangle of intersection should be observed. Referringthen to Table I the value of k can be obtained. This method has been found to give results suffi- v; j:iently accurate for all practical purposes, and with a :areful observance of the limitations pointed out above t may be used with confidence by the designer of 01, ! ighting systems. JSee Standard Relations of Light-Distribution; Arthur11 r. Sweet. Transactions Illuminating Engineering Society, No-i, -ember, 1909. ill. Uniform illumination is a result of correct designof the lighting appliance and its proper installation. In
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