We humans are a determinedly diurnal species. We love the light so much that we will find ways to produce it when nature isn’t providing it. In fact, we even use light as a symbol for truth and for good, while we make dark a symbol for evil. We seem not to understand that , when God created light, he did not replace the dark with it, but separated the dark from the light and created different creatures to function in each. Sadly, we soon developed artificial light sources to brighten our surroundings and give us an extension of our days. As with so much human activity, this has had both beneficial, and harmful effects on other creatures with which we share the world, and on us as well. A quick search of Wikipedia on the subject of light pollution gives summaries of some thirty studies of the effects on life from zooplankton to insects to birds to mammals to humans. I have no doubt there have been more studies than these, but a quick glance through a few of these is enough to make us aware of the need to think before we continue lighting up more and more vast tracts of cities, shopping malls, suburbs, etc.
The natural cycle of day and night is probably the most important environmental signal for all behavior of all life forms, determining plant growth, migratory behavior and general activity of animals, and mating activity of many species. Normally, the length of light cycles varies with the seasonal change and with lunar cycles. These natural variations trigger mating in many species and can be disrupted by introduction of artificial light, resulting in mating outside of the season most favorable for survival of the offspring.
Even humans can be adversely affected by the excessive presence of artificial light, as it makes it possible to work and play far into the time our bodies are “wired” to use for rest. The result is a disruption of the human circadian rhythm, making it more difficult to fall asleep. In the year 2000, an article was published in “The Journal of Neuroscience” concerning the mechanism producing this effect. A photosensor in the retina detects light, especially blue light, and signals the pineal gland to stop producing melatonin. The resultant low levels of melatonin in the bloodstream cause difficutly in falling, or staying, asleep. It was found that being exposed to the light from an incandescent bulb for just 39 minutes was enough to lower melatonin levels to 50%. Melatonin is also a powerful anti-oxidant and it is thought that its deficiency may be associated with an increased risk of some cancers, Certainly, lack of sleep increases stress level, which is known to decrease resistance to disease in general.
My own experience in raising moths has possibly been affected by the steady increase in light in our neighborhood. Over the ten or so years I have been doing this, fewer and fewer wild males have been attracted to the females I have placed on my back porch. During the same time, more and more neighbors have begun lighting their yard all night. Not exactly a controlled study I admit, but suggestive enough to make me decide to give up or find another spot for the breeding cage!
Having pointed out a problem, I wish I could give a solution, but I can at least say that many attempts are being made to find answers, such as new lighting technologies to reduce the jmpact on specific species and turning out lights in certain migratory corridors to avoid the confusion of wildlife that is caused by unnatural nightime light.