Abstract
Electromagnetic radiation in the visible spectrum induces a broad range of physiologic responses beyond image formation. With the advent of electrical lighting, the distinction between night and day is less dependent on the daily solar cycle, and this has introduced the problem of eliciting physiological responses by light exposure at biologically adverse times. For example, light exposure in the evening suppresses the hormone melatonin and can disrupt sleep. Such light-exposure induced physiologic responses in turn can have adverse health consequences ranging from depression to diabetes. Ongoing studies over the past three decades have identified novel receptors and neural pathways that mediate non-image forming (NIF) responses to light exposure, which are unique from those that mediate image forming responses. While various studies confirm that these responses all start at the retina and typically share a monotonic relationship, a common theme emerging from ongoing research is that there is considerable divergence at the level of the stimulus-response mechanisms, signal transduction pathways, and response characteristics. Moreover, each of these components are differentially modulated based on the characteristics of the photic stimulus including intensity, duration, pattern, and spectrum. While metrics and models that quantify and predict these responses, respectively, are warranted both for research and application purposes, the marked divergence between these responses raises the challenge of using surrogate measures that may be less resource intensive to collect. The session will briefly review the divergence in NIF responses to light exposure, current research and application challenges and future directions.