reasonable limits. Furthermore, instrumentation for evaluating "brightness" and "lumi- 

 nous flux density," especially of ultraviolet radiation, is not a readily available item of 

 commerce. Suitable equipment that is both reasonable in cost and appropriate for field 

 use is still being sought. 



Actually, progress in research in the entomological field has occurred simultaneously 

 with improvements in light sources and photoelectric measuring devices and with ad- 

 vancements in knowledge and standards concerning light measurement. Advances in the 

 understanding of light phenomena have already resulted in better understanding of insect 

 reactions studied by earlier investigators, as demonstrated by Von Frisch's theory 3 of 

 the role of polarized light in the orientation of bees and ants. Satisfactory explanations of 

 other known insect reactions will probably be found. 



ESTABLISHED PRINCIPLES CONCERNING "INTENSITY' 



Certain basic principles have been established by the studies conducted to date. It 

 has been found, through comparisons of different lamps, that attraction increases with 

 increases in both "brightness" and "luminous flux density" to a point and then diminishes; 

 however, the increase in attraction is not proportional to the required increase in 

 energy input. Figure 2 shows response obtained to "intensity" variations by Hollings- 

 worth. Experiments with very "intense" sources, approaching that of the sun, show 

 that activity of nocturnal insects ceases and day-flying insects become active. There 

 also appear to be definite limits to the distance from which insects can be attracted 

 to any light source. 



This pattern of diminishing response to increases in "brightness" and "luminous 

 flux density" is fundamentally related to efficient use of input power; naturally the 



n 

 W 



H 

 U 



H 



H 

 < 



< 



4.0 



3.0 



2.0 



1.0 



"b 



+ 



20,000 40,000 60,000 



INTENSITY (ARBITRARY UNITS) 



80,000 



100,000 



Figure 2. --Response of Microlepidoptera to white light of various intensities. 



3 Frisch, Karl von. Bees, Their Vision, Chemical Senses, and Language, Cornell University Press, 1956. 



30 



