Are night insects attracted to light or heat?
First, don’t forget that heat and light are both kinds of radiation. Heat is radiation in the infrared range of the spectrum … invisible to us, but it could theoretically be visible to insects. (I happen to know that it’s not … it is detectable to some reptiles, like vipers, but not to insects … but my point is that you would have to consider this in your experiment.) So the simplest experiment would be to have a cool light source (light but little heat), and a black heat source (a lightbulb covered with, say, a kitchen pot so that it gets hot, but does not leak light), and see which attracts the most insects.
