Artificial Light: Experimental Problems with Insects

Abstract

The use of artificial light sources in entomological research requires a thorough understanding of the complexities of artificial light, and artificial light sources should mimic natural light as closely as possible. Insect eyes and human eyes differ greatly in spectral sensitivity and possible experimental influences from these differences need to be minimized. An approximation of daylight can be achieved using a 1:1 mixture of “daylight” fluorescent lamps and “wide-spectrum grow light” fluorescent lamps. Instrumentation that is capable of measuring light intensity within the 300–650 nanometer (nm) range should be used, and light intensity should be reported in radiometric units. To allow the experiment to be reproduced, reported measurements of radiant energy from light sources should include the type of lamp, the voltage and type of electrical current (alternating or direct current) powering the lamp. The use of foot candles, meter candles, or lux should be discouraged as inappropriate for entomological studies. Light intensities should be manipulated to retain the same spectral emission across the entire array of experimental intensities; this can be achieved by using one to several layers of window screen as an intensity filter. Insect flicker fusion frequencies range from 20 cycles per second (cps) to 300 cps whereas human eyes have a flicker fusion frequency of 45–53 cps. The flicker sensitivity of insects under artificial light is important because alternating current-powered fluorescent lamps that use standard ballasts and alternating current powered-incandescent lamps flicker 120 cps. Fluorescent lamps flicker in a definite on-off pattern; incandescent lamp flicker involves short bursts of short-wavelength light (<450 nm). Two different methods are necessary to eliminate flicker from incandescent and fluorescent light.