1. The science of darkness and the positive responses of biological systems to the presence of darkness, and not merely the negative effects caused by the absence of light.
2. The study of light pollution at night as it directly impacts biological existence which is usually specifically affected by darkness.

Plants and animals are programmed to function in a certain pattern of daylight and darkness. Alter those patterns and unhealthy things often happen.

It applies equally to organisms that are active at night and those, including humans, whose bodies require regular periods with the lights out.

Some people believe that as with all types of pollution, light pollution contaminates the natural environment and produces side effects that should be mitigated or avoided, if possible, to create a balance between necessary urban light levels and a healthy environment.