In The Art of Scientific Investigation, (W.W. Norton, 1950), W.I.B. Beveridge writes that the reception of an original contribution to knowledge can be divided into three phases. First, it is ridiculed as untrue, impossible, or useless. Second, people then acknowledge that there may be something to the idea, but declare it would never be of any practical use. Third and finally, when the discovery has received general recognition, people say that the idea is not original and had been anticipated by others.
The reception of the newly discovered intrinsically photosensitive retinal ganglion cell (ipRGC) in the mammalian retina was no different. What is now considered general knowledge was ridiculed in the early 1990s. Russell Foster, a scientist at Imperial College in Great Britain, recounts how he was practically thrown out of a meeting room when he presented his results showing that animals with no functional rods and cones (the two types of photoreceptors in the human retina) were still able to shift the timing of their wheel-running activity in response to a light pulse. Vision scientists refused to accept that they had, for 100 years, missed a class of photoreceptor in the eye. In 2002, Brown University scientist David Berson (Trends in Neurosciences, Volume 26, Issue 6, Pages 314-320, June 2003) found the last piece of the puzzle: an entirely new class of photoreceptor, the ipRGC.
Studies were performed to better understand how the ipRGC responded to light and how it interacted with rods and cones. It is now well established that the ipRGC is sensitive to short-wavelength (blue) light and, although it is the main conduit of light signals from the retina to the brain, that it receives processed input from rods and cones. Simply put, the science surrounding the ipRGC led to a paradigm shift in how lighting is measured, manufactured, specified, and applied.
Based on this new knowledge, we at the Lighting Research Center (LRC) proposed a model of human circadian phototransduction (the means by which the retina converts light signals into neural signals for the circadian system) to quantify circadian effective light. The model is constrained by the neuroanatomy and neurophysiology of the human retina; the ipRGC is central to the model but not synonymous with the model. A new way of quantifying light’s impact on the circadian system called circadian stimulus (CS) allows one to predict how different spectral power distributions and light levels will suppress the hormone melatonin at night. We also developed the Daysimeter, a personal sensor that is calibrated to measure CS in the field. We have been working with the National Institutes of Health, the General Services Administration, the National Institute of Occupational Safety and Health, among others, to quantify the impact of CS on sleep quality and quantity, performance, fatigue, mood, and behavior in various populations, including older adults with Alzheimer’s disease, office workers, and cancer patients. We have also formed a Light and Health Alliance with a group of manufacturers to inform them of this new research. Finally, we are developing lighting patterns that will serve as tools for designers to learn how to implement 24-hour lighting schemes to promote circadian entrainment in the built environment.
Researchers, even the vision scientists, now believe ipRGCs are real. However, the application of this knowledge into lighting practice is still in Beveridge’s second phase. Lighting designers, manufacturers, and users embrace the idea that lighting isn’t just for vision, but lighting professionals are still struggling with how to implement the knowledge. For example, static, warm-color lighting systems installed in a ceiling are not necessarily going to be the optimal solution for circadian entrainment in schools and offices. Personalized, dynamic lighting delivered at the occupants’ desks would be more effective although portable, dynamic plug-in products are not yet widely available. When delivering light, designers should measure vertical light levels instead of horizontal footcandles on the workplane. Designers also need to specify not only when to deliver light, but when to deliver darkness. Undoubtedly, the ipRGC discovery resulted in a paradigm shift in science, but the application of this knowledge to lighting will only be fully embraced when that discovery is thought to have been obvious all along.
Mariana G. Figueiro is the Light and Health program director for the Lighting Research Center, and a professor at Rensselaer Polytechnic Institute, in Troy, N.Y.
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