Considerations and guidelines for photic measurement in field studies of the physiological effects of light

Guidelines for light measurement in laboratory studies of the non-visual effects of light have recently been put forward. Yet, outside of controlled environments, unique challenges necessitate additional consideration and modifications to those recommendations. The purpose of this paper is to build on prior work by outlining pre-ocular, ocular, and post-ocular factors and associated considerations that influence photic exposure and the physiological effects of light in the field. Practical constraints of applying laboratory measurement guidelines and tools and strategies for light measurement in field-based work are discussed in detail, including the trade-offs of different approaches. A standard operating procedure for measuring light in field studies is provided, with particular attention to managing sources of variability, along with an example that applies the procedure to a recent study. Finally, future directions and remaining challenges of photic measurement during field studies of sleep, circadian rhythms, and other non-visual effects of light are identified.