216 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
flashes, part is reduced. A reversible process occurs, and you will 
note that this is an extraordinary process from the chemical stand- 
point. Here is an animal with a lamp which burns an oil, and after 
that oil has been burned, the oil is reformed, and it is ready to be re- 
burned. We have the process of oxidation and reduction simply 
going back and forth according to the amount of oxygen which is 
present. Not only from the physical but from the chemical stand- 
point the firefly is highly economical. Like the Pheenix of old, luci- 
ferin is recreated from its ashes to pass through the cycle of another 
life. 
It is possible to devise a lamp in which luciferin is burned continu- 
ously over and over again. In one region luciferin is oxidized to 
oxy-luciferin with luminescence; in another the oxy-luciferin is re- 
duced to luciferin again. To be sure the light is weak, and practical 
difficulties appear in the “ poisoning ” of necessary catalysts, but the 
principle remains. Perhaps we may look to an application of this 
principle for the future development of new means of illumination. 
Apparently mysterious and often unusual in color, the light of 
living creatures is not essentially different from that of any ordinary 
light, except in its mode of production. We express this difference 
when we say that animal light is “cold light” or a luminescence. 
Electric ight is a “hot light” or an incandescence. Every sub- 
stance, no matter of what material, of any color or texture, whether 
it burns or not, emits light when its temperature is raised above a 
certain point (about 525° C). The first light at this low temperature 
is red, then yellow appears at a higher temperature, then white light 
at the 5,000° of our sun. The higher the temperature the brighter 
the light. This means of producing light is so universal and so easy 
that it is no wonder we have adopted it. Practically every illuminant 
in use to-day is patterned after the sun and stars. We heat an incan- 
descent lamp filament to the highest temperature possible without 
volatilizing the filament. It is not possible to attain the temperature 
of the sun, but 2,000° is attained, and a high percentage of the electri- 
eal energy which heats the filament is radiated. Unfortunately most 
of this radiation is heat, and only about 2 per cent is visible light. If 
the 98 per cent useless radiation could be eliminated, a 2-horse- 
power engine might run the dynamo to supply our lights that now 
require 100 horsepower. Incandescence is a wasteful way of produc- 
ing light because it is impossible to separate the heat radiation from 
the visible light radiation. 
Luminescence, or cold light, on the other hand, consists of nothing 
but visible light. The spectrum of a firefly lies wholly in the visible 
region with no infra-red or ultra-violet. As far as radiation goes it 
is all light or 100 per cent efficient, and this is the basis for the state- 
ment that fireflies are so efficient. 
