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late an efficiency value into a corresponding color temperature and hence to ascertain the distribution. Table 10 shows the relation between efficiency and color temperature. Gas filled and carbon filament lamps have been less accurately calibrated and are inherently more variable.

Table 10

Color Temperatures of Vacuum Tungsten Filaments at Various Efficiencies^[1]

Lumens per Watt (Uncorrected)	Color Temperature (Uncorrected)	Lumens per Watt (Corrected)	Color Temperature (Corrected)
0.5	1644	0.58	1663
1.0	1777	1.14	1794
1.5	1866	1.70	1883
2.0	1939	2.26	1955
2.5	1998	2.82	2014
3.0	2050	3.37	2066
3.5	2096	3.93	2112
4.0	2138	4.48	2153
4.5	2175	5.02	2190
5.0	2208	5.57	2224
5.5	2241	6.12	2257
6.0	2269	6.66	2285
6.5	2299	7.2	2315
7.0	2327	7.76	2343
7.5	2354	8.30	2370
8.0	2380	8.85	2397
8.5	2406	9.39	2423
9.0	2431	9.94	2449

The first two columns show the lumens per watt and color temperatures as directly determined experimentally from a given lamp. The second two columns give these same quantities corrected for losses due to cooling effects of leading in and supporting wires and absorption of the lamp bulbs.

3. Standards of Spectral Transmission

The characteristics of physical objects which determine their colors, when viewed by radiation from other sources, can be expressed almost completely by means of spectral reflection or transmission curves, representing as a function of wave-length or frequency, the fraction of the original radiation impinging upon the object, which finally leaves it as reflected or transmitted rays respectively. Such curves are most readily determined by means

1. Hyde, E. P., Cady, F. E. and Forsythe, W. E., Color Temperature Scales for Tungsten and Carbon, Phys. Rev., (2), 10, Table I, p. 401; 1917.