Seeing Blue At Night May Not Be What's Keeping You Up After All

We already know that a precise range of wavelengths within daylight triggers a light-sensitive photoreceptor in the back of your eye, causing the body's internal clock to reset. Those receptors are called "intrinsically photosensitive retinal ganglion cells" (or ipRGCs), according to Science Alert - although the actual color is perceived by some nearby cones (which then send information back to those rceptors). But are our bodies really affected specifically by the perceived color? Chronobiologist Christine Blume investigated with a team from Switzerland's University of Basel and Germany's Max Planck Institute for Biological Cybernetics: Modern scientific wisdom advises us to avoid devices that emit a significant amount of blue radiance, such as our smartphones, computer monitors, and tablets, when we ought to be wrapping ourselves in darkness and resting. There's perfectly sound reasoning for this - the ipRGCs in our eyes react to short wavelengths of electromagnetic radiation, roughly 490 nanometers in size... Given blue light scatters from the sky during daylight hours, it makes sense our eyes would use this wavelength as a cue to mark the beginning and end of sleep time... Yet University of Basel chronobiologist Christine Blume had her suspicions that the way a light's mix of wavelengths influenced the color-reading cones could mean there's more to the phenomenon than meets the eye. "A study in mice in 2019 suggested that yellowish light has a stronger influence on the internal clock than bluish light," says Blume. To resolve whether the way cones perceive a range of wavelengths carries any weight in how the blue-triggered ipRGCs function, Blume and her team recruited eight healthy adult men and eight women in a 23-day-long experiment. After habituating to a specific bedtime for a week, the volunteers attended three visits to a lab where they were exposed to a constant controlled 'white' glow, a bright yellow, or dim blue light for one hour in the evening... None of the analyses revealed any indication that the perceived color of the light affected the duration or quality of the volunteers' sleep patterns. Instead, all three light conditions caused a sleep delay, suggesting light in general has a more complicated impact than previously thought. That's not to say ipRGCs aren't affected by 'blue' wavelengths of light. Rather, white light that is packed with blue waves but stimulates cone cells into seeing yellows, reds, or purples could still affect our sleep cycles. Similarly, light that looks blue but isn't intense enough to provoke the ipRGCs into functioning might have little influence over our body's daily rhythms. Phones of the future may one day allow us to switch into a night mode that we don't perceive in warmer tones. Thanks to long-time Slashdot reader schwit1 for sharing the article.

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