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Scientists at the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute have taken a significant step forward in understanding how light affects the human body. The scientists developed a model that postulates the mechanisms by which humans process light for the circadian system, the body's system that regulates rhythms such as body temperature, hormone production, alertness, and sleep patterns. The research will be featured in Brain Research Reviews.

The "circadian phototransduction" model offers a framework for testing and exploring the practical aspects of architectural lighting and how it can affect human health. "The model is important in two ways," said Dr. Mark Rea, director of the LRC and lead researcher on the project. "It is theoretically important for generating hypotheses about neural mechanisms; and it is practically important for predicting the relative effectiveness of different light sources for impacting the human circadian system."

Rea says the model can be used as the foundation for a new system of circadian photometry, the study of how light affects the circadian system, much like the current system of photometry based on human vision. Quantification of light as a stimulus for the circadian system has profound implications for exploring how lighting can be used to adjust our bodies' internal clocks. "The model takes into account the high sensitivity of the human circadian system to short-wavelength (blue) light," explained Rea. "But it also considers evidence for a phenomenon known as spectral opponency. When middle-wavelength (yellow) light is added to short-wavelength light, the resulting white light is actually less effective at regulating the circadian system."

According to LRC researchers, the model is based on recently published evidence from electrophysiology and neuroanatomy. It incorporates newly-discovered retinal neurons that respond directly to light exposure called intrinsically-photosensitive retinal ganglion cells, or ipRGCs, as well as traditional photoreceptors (rods and cones).

LRC scientists plan to extend and refine the circadian phototransduction model, as well as bridge the findings to practical applications.

The research is summarized in a paper titled, "A model of phototransduction by the human circadian system," available in the Brain Research Reviews journal online and will be published in an upcoming print edition of the journal.