Light is life. When you think of life on this planet- plants, animals, humans- they are all impacted by light and the cycle of the sun. Light is the oldest input, and a significant nutrient for biological functions throughout the web of life.
Light is the most powerful time cue for our 24-hour circadian clock. It tells us when to wake up, when to get sleepy, when to produce certain hormones and when to lower or raise our temperatures. It regulates our sleep, which is imperative for health and cognitive function, as sleep aids in healing, restoring and rejuvenating the physical body and our mental capacity.
The most impactful wavelength to humans’ biology in the visible spectrum is blue. Within the visible spectrum, 480 nanometers (visibly blue) is most impactful to humans and circadian rhythm regulation, and its presence or absence triggers a multitude of biological responses.
Light has two main effects on alertness. Firstly, light as a stimulant increases alertness and improves performance, depending on its wavelength and intensity. Blue-enriched light (specifically blue light around 480 nanometers, the peak of melanopsin sensitivity) and high intensity light directly alerts the brain and can be used at times when alertness and productivity need to be heightened; for example, during daytime or at work.
Light has a second effect on alertness via its impact on our 24-hour circadian clock. Alertness and performance rhythms are strongly regulated by the clock, so when the clock is shifted (e.g. staying up later or waking earlier), the timing of peak alertness and performance shifts accordingly. Maintaining exposure to a stable light-dark cycle (bright blue-enriched days and dark nights, and a habitual sleeping pattern) is needed to maintain good circadian entrainment, including alertness and performance patterns.