“What?”, “Why?”, and “How?”: An Argument for Employing Physiological Techniques in Research about Visual Response to Light

“While you are experimenting, do not remain content with the surface of things. Don’t become a mere recorder of facts, but try to penetrate the mystery of their origin.”—Ivan Pavlov (1849–1946)

For many years, lighting researchers have focused on answering “What?” questions. For example, what lighting conditions cause discomfort? What attributes of light cause an environment to evoke feelings of privacy? What light spectrum will lead to preferred object coloration? Questions like this are natural and necessary at the beginnings of understanding.

Answers to second-order “What?” questions provide refined understanding. What luminance defines the threshold between comfort and discomfort? What luminance ratios and gradients are associated with perceptions of uniformity or nonuniformity? What degree of chroma enhancement is too little, too much, just right? Answers to these questions provide actionable insight about lighting conditions that are likely to be acceptable, or even preferred. Accumulated knowledge from researchers and designers, coupled with horse sense and vetted through consensus, manifests in illuminance recommendations, luminance ratio recommendations, color rendering criteria, and limits on luminaire luminance and luminous intensity, to name just a few examples.

Applied lighting research seldom seeks to understand the causal mechanisms of human physiology and psychology that would explain how people respond to their lit environment. This prompts deeper “What?” questions that are largely unanswered, or even unasked. What are the physiological and cognitive markers for discomfort, or perceptions of visual amenity, or color preference? What metabolic states, brain functions, and stress biomarkers relate to lighting quality? As a complement to subjective opinions and self-reported responses, physiological techniques have the potential to enrich our understanding of how people experience light.

Research that propels new understandings must begin with clear questions. To move forward, we need to move beyond questions of “What?” to questions of “How?” and “Why?” How does a person’s body react when exposed to lighting conditions perceived as pleasant? Or when exposed to glare that we expect will cause discomfort? Or when spectrum renders object colors in a preferable way? More deeply still, why do people experience involuntary changes in their physiological functioning when exposed to different lighting conditions? From broad questions can come testable hypotheses, and from testable hypotheses one can design experiments that systematically manipulate attributes of the luminous environment (i.e., independent variables) while concurrently isolating physiological responses (i.e., dependent measures)—permitting inferences between cause and effect.

In the future envisioned, our independent variables will continue to be rooted in radiometry, photometry, and colorimetry, though modern technology will enable lighting conditions to be manipulated with ever-finer granularity. On the other hand, dependent measures will include things like eye tracking, galvanic skin response, heart rate and body movement monitoring, electrocardiogram and functional magnetic resonance imaging scans, and swabs of salivary cortisol. Indeed, some of this work is already occurring. More is needed.

This future will be best accomplished with multidisciplinary teams that include people with complementary skills in psychophysical- and physiological-based research methods. Those involved in mentoring early career lighting researchers can encourage their protégés to embraces a multidisciplinary mindset that include experimental paradigms from psychology and physiology. Early career researchers can make it a priority to develop actionable expertise.

Returning to Pavlov, by starting with “What?” lighting researchers have collectively recorded a body of useful facts and insights about what constitutes acceptable lighting for vision. Multidisciplinary collaborations that permit the concurrent study of psychophysical and physiological responses to the lit environment have the potential to penetrate the deeper questions of “How? and “Why?”