maximum attraction per watt of input would be desired. Consider a source radiating 

 in all directions at unit input power to which insects are attracted from unit distance. 

 If a change in input power is assumed to give a proportional change in light output (never 

 achieved), then, by the inverse -square law of radiation, doubling the input power should 

 increase the distance from which insects are attracted by a factor of the square-root of 

 2 (= 1.41) and the potential insect catch should be similarly increased. Thus, to catch 

 the same proportion of the insect population at all levels of input power it is necessary 

 that the catch vary as the square -root of the change in power input. This does not happen. 

 Therefore, power is more efficiently used by distributing several low-power installations 

 over an area than by concentrating an equal input in a single source. 



The efficient use of power is of special importance where operations are carried on 

 in isolated locations by use of storage batteries. 



It is also known that the relative attractiveness of lamps of different "intensity" is not 

 the same when the lamps are placed in competition with each other at relatively close 

 distances as it is when the lamps are isolated from each other. When a large lamp and a 

 small lamp are placed close together, the small lamp usually attracts a much smaller 

 comparative catch than will be the case if the two are placed out of sight of each other. 



Two other fundamentals are dictated by the difference between the concepts of 

 "brightness" and "luminous flux density." "Brightness" of a source is affected only by 

 changing the amount of luminous flux emitted from its radiant body. Incandescent and 

 mercury-vapor lamps increase in "brightness" with increasing wattage ratings, but not 

 in direct proportion to the wattage increase. Fluorescent lamps, which increase in 

 physical size in almost direct proportion to their wattage rating, are of relatively the 

 same "brightness" in all sizes. "Brightness" of either type of lamp is affected by changing 

 the lamp current. Taylor 4 found in 1956 that doubling lamp current of 15-watt BL lamps 

 increased ultraviolet output approximately 80 percent. 



"Luminous flux density" is affected by anything which increases the total radiant 

 energy flux through space. Thus, different "illumination" levels can be obtained by using 

 multiples of similar lamps without altering source brightness. On the other hand, 

 "illumination" may or may not be altered by changing the "brightness" of the source, 

 depending upon the accompanying change in physical size of the source. 



PRACTICAL CONSIDERATIONS CONCERNING "INTENSITY" 



As the result of field experience and the considerations of most efficient use of input 

 power previously mentioned, low-wattage ultraviolet sources are becoming generally 

 accepted as attractants instead of high-wattage mercury-vapor lamps. Fluorescent BL 

 lamps are widely used as general insect attractants and these are particularly efficient 

 sources of 3650 A. radiation because of the conversion action of their phosphor. Special- 

 ized traps for the pink bollworm are using argon glow lamps, which are also low-wattage 

 sources. 



In insect survey operations two diametrically opposed needs are becoming apparent. 

 Fluorescent BL lamps of the 15-watt size have been widely used for routine survey 

 operations, particularly of insect migrations. Survey entomologists have long been 

 troubled by the fact that these traps provide catches that are too large for adequate 

 analysis by available personnel. Consequently, considerable consideration has been 

 given to using a smaller lamp if the smaller catch from a lamp proves to be equally 

 representative. On the other hand, in survey work to detect small populations of new 

 or particularly undesirable insects, or in attempts to control insect damage, the 



4 Taylor, John G., Annual Report, Line Project AE dl-2, 1956, Farm Electrification Research Laboratory, AERD, USDA. 

 (Unpublished). 



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