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Sandhi Prakash: Between Lightness and Darkness
According to Ayurveda, a sandhi is the gap or transition period between circadian cycles. And prakash means light so a sandhi prakash is the period between lightness and darkness that occurs at sunrise and sunset.
This is a sacred time, in which many cultures practice health, wellness, and spiritual rituals. In fact, new science shows us that practicing rituals at sunrise and sunset can enhance their already powerful health benefits.
In a 50-year review of the science of rituals, published in the Journal of Family Psychology, rituals were linked to stronger immunity, greater marital satisfaction, better self-worth, stronger family bonds, reduced anxiety, and more resilience to failure.
Historically, sunrise and sunset rituals include meditation, the asana practice of surya namaskara (sun salutation), pranayama, mantra chanting, prayer, agnihotra fire ceremony, gandharva veda music (sunrise, sunset melodies), sun gazing, and many more.
Practicing rituals during these transition periods of sunrise and sunset have become standard because they work. Every morning, thousands line up on the river Ganges and throughout India to greet the sun with a salutation. The fire ceremony called agnihotra described in the Veda’s thousands of years ago is still practiced by thousands each day at sunrise and sunset.
In nature, the period of time during the sunrise and sunset are uniquely different than other times of day. Most commonly, the wind is calm, the air is still, the lakes and oceans are flat and there is a palpable experience of peace and calm during these two transition periods. Ayurveda suggests engaging in rituals like yoga, pranayama, and meditation during these periods is a way to entrain the silence of nature into our beings.
The Science Behind Melatonin, Circadian Rhythms, and Blue Light
Circadian Medicine is based on the science that the body’s biological clocks are set to flip on or off based on billions of years of the precise, but changing, timing of sunrises and sunsets. Based on the sun’s predictability, the body’s biological clocks adjust in advance of environmental changes. Sunrise and sunset are the master circadian switches that regulate the majority of the body’s physiological functions.(2)
It turns out that he body is most sensitive to the blue light. The master circadian switch, called the suprachiasmatic nuclei (SCN), triggers the release of melatonin—which sets sleep cycles and more–and is blocked by blue light.
In recent years, negative exposure to blue light from LED light bulbs, computer screens, and cellphones has been excessive, resulting in compromised melatonin production. Studies have now linked exposing the body to blue light at night to mood-related states of worry and sadness. A recent study in the journal Nature found that long-term exposure to blue light can cause retinal and brain damage in in fruit flies. The SCN is so sensitive to blue light that just one LED button on a computer can block melatonin at night and affect sleep.
During sunrise and sunset, there is significantly less blue light than during midday.
Blue and violet light from the sun have shorter wavelengths. These are blocked by the atmosphere when the sun is low in the sky during both sunrise and sunset. The lower the sun is in the sky, the more atmosphere the rays must penetrate. Because yellow, orange, and red rays have longer wavelengths, they more easily penetrate the atmosphere at dawn and dusk and we see a redder sky at sunrise and sunset.
Studies tell us there is more blue light exposure during sunrise compared to sunset, although both are predominately yellow, orange, and red. There is, more melatonin-blocking blue light at sunrise for a couple of reasons. Throughout the night, the air becomes more calm, and dust and other particulates settle, allowing blue light not to be blocked as significantly.
On the other hand, prior to sunset there is more turbulence and particulates in the atmosphere, which help to block blue light. At sunset, the lack of blue light allows melatonin to begin its evening surge and helps you to sleep. The small amount of blue light that does reach the earth during sunrise, along with vitamin D levels, blocks the production of melatonin and allows us to wake up refreshed, making way for more cortisol to fuel the day’s activity.
The difference in blue light at sunrise and sunset can also be attributed to the Earth’s relationship to the sun. During sunrise, we are moving toward the sun as the Earth spins from west to East, while at sunset, we are moving away from the sun, as explained by A. Ramachandraiah, PhD, a professor at the National Institute of Technology in Warangal, India.
The Importance of Contrast
Emerging research suggests that much of the regulation of the circadian clocks in the body are based on contrast as well as color. Early in the evolution of mammals, we did not see as many colors as we do today. Research has discovered that the contrast between blue and yellow light changes dramatically during the day and the SCN is as sensitive to these changing contrasts as it is blue light.
The light contrasts we are exposed to at sunset and sunrise are quite different. A new study published in Current Biology shows that at sunrise the light shifts from black to blue to yellow and at sunset it shifts from blue to yellow to orange, before shifting to blue and then black. During these transitions, researchers found that the blue-yellow contrasts are significantly greater and that these contrast shifts trigger the SCN to regulate melatonin production, keeping the biological clocks in rhythm with nature’s circadian rhythms.
Animals and humans alike have evolved extremely complex systems to be prepared for environmental changes—from shifts in light to shifts in seasons, temperatures, and growing seasons. According to Ayurveda, the gap between these transitions provides us an opportunity to better sync our biological clocks to nature’s rhythms. Living is sync with nature in this way allows nature to stay in sync as well—we live breath and evolve based on these connections.
The benefits of rituals are well-documented. Adding a sunrise and sunset ritual to your routine may provide an even greater connection and appreciation to nature, spirit, and yourself. Try it and let us know how it changes your day!