“Light is not so much something that reveals, as it is itself the revelation.” – James Turrell
This Letter emerged from a lecture. At South by Southwest 2026, Mark Reynoso, CEO of Korrus, led the session Awakening to Light: Returning to Nature’s Rhythm. The reflections that follow begin with that encounter and expand into broader directions, spanning chronobiology, architecture, and the long history of humanity’s relationship with light.
Never before have we exercised so much control over light. We can extend the day late into the night, work at any hour, cross time zones within hours, and spend entire weeks in environments where the sun no longer determines much of anything. We have gained convenience, mobility, and productivity.
A phrase by James Turrell, the artist who devoted his life to sculpting with natural light, offers a useful inversion. Light is not merely an instrument that illuminates the world. It is itself part of what is revealed. Somewhere along the way, perhaps, we lost sight of that perception.
We increasingly live detached from the natural cycles that regulate the human body, and the cost of that separation appears in symptoms that often seem unrelated: fragmented sleep, elevated cortisol, chronic low grade inflammation, metabolic dysfunction, and persistent fatigue. Taken together, however, they suggest a common origin, the growing mismatch between the lives we lead and the biology we inherited.
A Brief History of Light
For most of human history, light was not merely an environmental condition; it was the very structure of time itself. Sunrise organized wakefulness, movement, and work, while dusk prepared the body for rest and deceleration. Even after fire, candles, and later oil lamps extended human activity into the night, darkness still imposed limits. The alternation between light and dark remained imperfect, yet unmistakable. There was a recognizable interval between activity and rest, between exposure and retreat.
Electricity changed that equation on an entirely different scale. Light ceased to be solely a natural phenomenon and became a tool of convenience. The nineteenth century illuminated factories and streets; the twentieth brought that transformation into offices, homes, storefronts, and cities that no longer grew fully dark; and the twenty-first century intensified the process through portable screens, permanent connectivity, and lives spent increasingly indoors.
In his lecture, Reynoso proposed a compelling interpretation of this trajectory: over the past few centuries, we have become increasingly detached not only from nature itself, but from the rhythmic experience of life, gradually replacing the cadence of the natural world with the demands of clocks, cities, and continuous production.
The analogy Reynoso drew at SXSW was particularly precise. Artificial light, over the last century and a half, has followed a path similar to that of industrial bread. Modern bread still resembles the original product, but much of what once made it nutritionally complete has been stripped away along the way. The same has happened with the lighting that illuminates contemporary life. It preserves the function of illumination, yet delivers only a fraction of the spectrum sunlight naturally provides to the human body, discarding, in the name of energy efficiency, wavelengths that carry important biological information.
“So literally, as humans, we have four macronutrients: food, water, air, light.” – Mark Reynoso
Reynoso’s argument moves light out of the realm of aesthetics and into that of physiology. We tend to think of lighting as a matter of ambience, shaped by visual preference or energy efficiency. In reality, light is one of the oldest and most fundamental signals the human body has learned to interpret, operating on the same level as what we eat, drink, and breathe.
The light that enters through the eyes does far more than enable vision. It carries dense biological information that the body continuously reads, calibrating hormones, regulating internal temperature, organizing sleep and wake cycles, and signaling to the digestive system when to activate and when to rest.
The Clock We Carry Within
The discovery that human beings are governed by biological clocks is not new, but only recently has it acquired deeper scientific understanding. In 1729, the French astronomer Jean Jacques d’Ortous de Mairan observed that a plant continued opening and closing its leaves in regular cycles even under constant darkness. The plant carried an internal clock. More than two centuries later, in 2017, Jeffrey Hall, Michael Rosbash, and Michael Young received the Nobel Prize in Medicine for mapping the molecular mechanisms underlying circadian rhythms in mammals. The term comes from the Latin circa diem, meaning “around a day,” and describes a set of physiological processes that repeat approximately every twenty four hours across nearly every tissue in the human body.
“Look deep into nature, and then you will understand everything better.” — Albert Einstein
Einstein’s intuition resonates deeply with contemporary biology. The conductor of the circadian rhythm resides in a tiny region of the brain known as the suprachiasmatic nucleus, located just above the optic chiasm. It receives signals directly from the retina and uses them to regulate the production of melatonin, cortisol, insulin, sex hormones, body temperature, cardiac activity, and countless other physiological functions. The circadian rhythm operates, therefore, as infrastructure. It works silently, sustaining nearly everything that happens within the body, from mood to immunity.
Matthew Walker, one of the leading voices in sleep science, captures this idea well by describing sleep not as a passive interruption, but as a central process for physical and mental balance. In Why We Sleep, he explains how sleep helps recalibrate emotions, strengthen the immune system, regulate metabolism, and control appetite. In other words, sleeping well is not merely a form of rest. It is what allows an essential part of human biology to continue performing its work.
Satchin Panda, of the Salk Institute and author of The Circadian Code, expands this perspective from another angle by linking circadian disruption to an astonishing range of conditions, including obesity, type 2 diabetes, cardiovascular disease, depression, certain forms of cancer, and cognitive decline.
Life Under A Roof
The World Health Organization, along with several subsequent studies conducted in Europe and North America, estimates that modern adults spend roughly ninety percent of their lives indoors.
Indoor lighting typically ranges between 100 and 500 lux. Sunlight, even on an overcast day, easily exceeds 10,000 lux, and under a clear midday sky can surpass 100,000. The gap is so vast that, in indoor environments, the body receives very little information about the actual time of day. At night, monitors, lamps, and screens continue signaling to the brain that it is still daytime, suppressing melatonin production and delaying sleep onset.
Frank Lloyd Wright, one of the most influential architects of the twentieth century, once wrote that light is increasingly what gives beauty to architecture. His designs began with the sun before they began with the land itself. Homes such as Fallingwater, in Pennsylvania, were conceived to follow the movement of light throughout the day, with windows that extended the outside world into the living space.
Wright’s intuition, formulated decades before the emergence of chronobiology, anticipated a perception that science now confirms with remarkable precision: the quality of the light we receive shapes the quality of the life we experience beneath it. Most contemporary buildings, designed around very different priorities, seem to have forgotten that lesson.
The result is a quiet form of misalignment. The human body, programmed to alternate between activity and rest in sync with the solar cycle, now operates in environments that provide few clear signals of whether it is morning, afternoon, or night. Studies involving night shift workers, considered by the World Health Organization to represent a model of circadian disruption, consistently show an association with increased risks of metabolic disease and cancer. What these workers experience in its most extreme form is, in many ways, a concentrated version of what many people encounter more diffusely throughout modern life.
Small Returns To Rhythm
The encouraging news is that the circadian system is remarkably adaptable. It responds quickly to changes in habit, and some simple practices produce effects disproportionate to the effort they require. It is worth considering them in chronological order, following the natural sequence of the day.
Morning is the most sensitive moment. Andrew Huberman, a neuroscientist at Stanford, recommends receiving between two and ten minutes of direct sunlight within the first hours after waking, without the filter of windows or sunglasses. This seemingly trivial act recalibrates the biological clock, advances the morning cortisol peak, and improves sleep quality the following night.
Russell Foster, neuroscientist at Oxford and author of Life Time, complements this recommendation with another equally well established practice: maintaining consistent sleep and wake schedules, including on weekends. Irregularity between weekdays and weekends creates what researchers call social jet lag, a chronic misalignment between social and biological rhythms.
Food functions as a second hand on the body’s internal clock. In several studies, Satchin Panda demonstrated that concentrating meals within a shorter eating window, ideally aligned with daylight hours, improves metabolic markers and sleep quality. The first meal tends to be more beneficial when consumed some time after waking, while the final meal is better taken several hours before sleep.
Afternoon requires attention to transition. Avoiding caffeine beginning in the early afternoon, a recommendation frequently emphasized by Matthew Walker, helps the nervous system decelerate as night approaches. Light, once again, is central. Reducing exposure to bright light during the two or three hours before sleep preserves the body’s natural melatonin curve. Replacing cool lighting with amber or indirect light later in the day is a subtle yet effective adjustment.
The bedroom, finally, matters more than we often imagine. A cool, dark, and quiet environment supports deep sleep, the phase during which the most important processes of cognitive consolidation and cellular repair occur. Charles Czeisler, Harvard professor and one of the leading authorities in applied chronobiology, notes that even small sources of nighttime light, such as the LEDs of electronic devices, can be sufficient to alter the quality of that sleep.
There is, finally, one practice that brings together nearly all of these elements in a single gesture. Walking outdoors during the day, even under cloudy skies, recalibrates the system more effectively than almost any supplement.
There is also a subtle pattern among business leaders known for the longevity of their careers. Warren Buffett has maintained a remarkably consistent and uncomplicated routine for decades. Jorge Paulo Lemann made tennis and outdoor sports an inseparable part of his personal discipline. Ray Dalio describes daily meditation as one of the pillars that sustained the clarity with which he led Bridgewater for nearly five decades. Music producer Rick Rubin, mentioned by Reynoso, recommends beginning the day in sunlight, even if only for a few minutes. These habits, seemingly unrelated at first glance, share a common root: they protect rhythm, and rhythm, over time, takes care of almost everything else.
What Does This Have To Do With Longevity?
Longevity extends beyond life expectancy alone. There is perhaps a more meaningful measure: healthspan, the number of years lived with functional health. Wealth accumulated over decades holds limited value if those who built it are no longer able to enjoy it, make decisions about it, or consciously pass their choices on to the next generation. From this perspective, caring for biological rhythm begins to resemble what we understand as long term stewardship. At its core, it is a form of capital, one that compounds quietly through discipline and erodes just as quietly when that discipline breaks down.
In an era where productivity and speed are often mistaken for progress, returning to the respect for natural cycles may appear regressive. Contemporary research suggests the opposite. Cognitive performance, decision making, emotional resilience, and physical health all depend on a body operating in rhythm. Accepting that certain rhythms lie beyond our control, and that the wisest course is to work with them rather than against them, may be one of the most mature forms of practical intelligence.
A Final Observation
At its best, wealth management is a practice shaped by time. No truly sound decision can exist without the patience required for it to mature. Market cycles, generational transitions, the building of institutions, and the continuity of families all follow a logic that has little in common with the speed of everyday life. Those who work with long term horizons eventually learn that time is less an adversary than a quiet collaborator.
The parallel with the human body goes beyond metaphor. The same principles that sustain enduring wealth, patience, consistency, attention to subtle signals, and the refusal to force cycles, also apply to the health of those responsible for preserving it. In both cases, what endures depends less on sudden movements than on the discipline of respecting the proper rhythm of things.
In a world illuminated twenty four hours a day, perhaps the most sophisticated gesture is to relearn how to live in harmony with the light the body has known for millennia. There is a quiet form of intelligence in that gesture, far removed from nostalgia. Nature did not invent rhythm. Nature is rhythm. And there are good reasons to believe that living well, for a long time, depends on learning to hear it again.
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Starting with the previous edition, we began dedicating the second theme of our Semiannual Letters to longevity, a concept deeply connected to our purpose of preserving wealth and legacy across generations.
More than a biological matter, longevity invites reflection on time, purpose, and continuity, principles that also shape the way we care for families and their stories at Turim.
For those interested in exploring this dialogue further, we invite you to listen to the Valores no Tempo podcast, available on the major audio platforms, where each season includes an episode dedicated to longevity and its implications from different perspectives.