Comparative tests of carbon, metallized carbon and tantalum filament lamps . on fac-tor (the constant for changing mean horizontal candle power tomean spherical candle power) of the lamps during their life givesa good indication of the way the distribution changes. Followingis a table of these values for three periods of life. TABLE 3 Lamp Spherical Reduction Factors New 400 Hours 800 Hours Carbon .810 .805 .794 Metallized .803 .805 .801 Tantalum .787 .811 .865 The causes of this change in the distribution of the intensityin the tantalum lamp must be due principally to the change in thecharact
Comparative tests of carbon, metallized carbon and tantalum filament lamps . on fac-tor (the constant for changing mean horizontal candle power tomean spherical candle power) of the lamps during their life givesa good indication of the way the distribution changes. Followingis a table of these values for three periods of life. TABLE 3 Lamp Spherical Reduction Factors New 400 Hours 800 Hours Carbon .810 .805 .794 Metallized .803 .805 .801 Tantalum .787 .811 .865 The causes of this change in the distribution of the intensityin the tantalum lamp must be due principally to the change in thecharacter of the surface of the filament after burning. The micro-photographs of the filaments shown in Fig. 30 indicate how rough-ened and pitted they become after burning for a few hundredhours. The in-egularities of the surface cause the light to beradiated and reflected from their surfaces more and more in a di-rection parallel with the length of the filament as the period ofbuining increases. This, of course, shifts the maximum of in- ILLINOIS ENGINEERING EXPERIMENT STATION. Fig. 6 Horizontal Distribution of Carbon Lamp When NewAND After 800 Hours op Burning AMRINE—COMPARATIVE TESTS OF LAMPS 11
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