Abstract: Moonlight exerts profound ecological, behavioral, and physiological effects on animals. However, due to the moonlight cycles’ complex changes in the intensity and timing of illumination, it is challenging to re-create and manipulate artificial moonlight in the laboratory. Consequently, only a limited number of controlled experiments investigated the effects of the moonlight cycle, and existing studies often oversimplify moonlight re-creation. To address the lack of open-source software-hardware solutions for re-creating moonlight cycles, we developed MoonShine, a Python program running on a Raspberry Pi computer that controls the intensity of an array of individually addressable LEDs positioned in diffusion boxes. MoonShine uses a companion program, MoonSim, written in R, to predict moonlight and/or solar ground illuminance (in lux) at one-minute intervals, through a defined time range, at any geographical location. MoonSim converts these illuminance predictions to specific LED intensity values and saves them to a .csv schedule file. MoonShine uses this file to control the LED array. MoonShine has several features to enhance the realism of natural light cycle re-creation. It can simulate not only moonlight but also daylight and twilight, thereby reproducing full diurnal light cycles. MoonShine can simulate open-field moonlight scenarios, as well as the effects of horizon obstructions, such as a ridgeline. Additionally, MoonShine has an adjustable stochastic cloud control model to re-create passing clouds. MoonShine also allows for the adjustment of the LED RGBW intensity ratios, enabling color shifting of the lunar/solar light spectrum to simulate, for instance, habitat-specific conditions. To demonstrate the accuracy of MoonShine‘s moonlight re-creation, we present calibrated radiometer readings from a nine-day moonlight schedule. To test the accuracy of MoonSim, we compare its predicted illuminance to radiometer measurements from a remote equatorial site with low atmospheric and light pollution. MoonShine and MoonSim are invaluable tools for biologists that need to manipulate artificial moonlight as an experimental variable in controlled laboratory studies, re-create artificial moonlight, sunlight, and twilight for raising or breeding animals, and calculate ground moonlight illuminance for use as a predictor variable in ecological studies.
