12 SCIENCE PROGRESS 



lamp can compete with either the open type or enclosed 

 arc on the score of cost, because it must be remembered that 

 to the figures given in the second table something has always 

 to be added for maintenance costs whereas the figures given 

 in the first table represent total cost. The fact that the 

 tungsten lamp can now be made in 500-1,000 candle power 

 units renders it all the more efficient as a competitor. There 

 are few interiors so large that a 1,000 candle power lamp is 

 not a sufficiently large unit for a satisfactory distribution of 

 the lighting and there are numerous cases of outdoor lighting — 

 as, for example, the lighting of side streets — in which this unit 

 is amply large enough. The competition of the large tungsten 

 lamp is likely therefore to grow steadily more effective, 

 especially as confidence in the lamps increases and users 

 cease to be afraid of the possibility of frequent heavy charges 

 for renewals. It may be argued that the open and enclosed 

 arcs are already necessarily doomed to extinction by the flame 

 arc but it must be remembered that the flame arc is a far larger 

 unit than any other, 1,000 candles being about the minimum 

 and the candle power ranging up to 2,000 or 3,000 candles. 

 Consequently it is not suitable for any but the largest interiors 

 and is also too large for side street and similar lighting. 

 Wherever a unit of 1,000-3,000 candles is not too large, how- 

 ever, the flame lamp must be expected to sweep everything 

 else before it. 



The question of the colour of the light is also an important 

 consideration. The yellow flame arc is brilliant but not too 

 pleasing. One advantage it possesses is a great fog-penetrating 

 power but against this must be set the disadvantage that it 

 produces a certain falsification of colour values. The white 

 flame arc is neither so efficient nor quite so satisfactory in 

 general working as the yellow, nor is the white absolutely 

 a true white : about as good as the colour of the light from 

 the tungsten lamp, it is not equal to that from the enclosed 

 arc, which still remains the nearest approach to daylight of 

 any artificial illuminant. Even the enclosed arc may be ex- 

 pected to continue in extended use especially where colour 

 value is of special importance, as, for example, in drapery 

 shops and so forth. It may be noticed in passing that the 

 red flame arc is used almost exclusively in butchers' shops. 



In all the figures which have been given the mean spherical 



