Functional Medicine

Your Light Diet: How the Modern Light Environment Is Harming Your Health

By Dr. Cameron Chesnut | Five Codes Podcast

We talk about food diets, sleep hygiene, and exercise protocols. We rarely talk about our light diet, the sum of what wavelengths of light we are exposed to, at what times, and at what intensities throughout the day. But light is one of the most powerful inputs into human biology, and ours has gone badly wrong.

This post is about the bigger picture that makes red light therapy make sense: the light environment we evolved with, what has replaced it, and what the consequences are. It is the most shareable post in this series and possibly the one that will matter most to your daily life, even if you never buy a single device.

This post is part of our complete red light therapy series.

We Had One Light Source for Almost All of Human History

For the vast majority of human existence, we had one light source: the sun. Its output is a broad, smooth spectrum covering ultraviolet through visible through infrared wavelengths. But the composition of that spectrum changes dramatically throughout the day.

At sunrise and sunset, when the sun is at a low angle to the horizon, the short-wavelength high-energy light (ultraviolet and blue) is largely scattered and absorbed by the greater length of atmosphere it travels through. What reaches us at dawn and dusk is heavily weighted toward longer wavelengths: red and near infrared light.

At solar noon, when the sun is high and its path through the atmosphere is shortest, the full spectrum arrives with more balance, including more ultraviolet and blue light.

Our second major light source was fire. Campfire, torchlight, candlelight, and eventually incandescent bulbs all emit spectra that closely resemble low-angle sunlight: smooth, broad, and dominated by red and warm wavelengths with minimal blue content.

Our biology was calibrated to this light environment over hundreds of thousands of years. Every photoreceptor in our eyes, every light-sensitive molecule in our cells, every circadian mechanism in our physiology was shaped by exposure to this spectrum.

What Replaced It: LED Lighting and the "Junk Light" Problem

Modern LED lighting, the kind used in the overhead lights in virtually every office, home, school, and hospital in the developed world, emits a radically different spectrum.

Standard white LED light is not a smooth, broad spectrum. Under a spectrophotometer, it shows a narrow, spiky output concentrated in the short-wavelength blue range, with minimal to no red or near infrared content. The "warm white" and "cool white" labels on consumer LED bulbs describe slightly different color temperatures but both remain fundamentally blue-heavy and red-deficient compared to natural light or incandescent bulbs.

This is what I call "junk light". Just as highly processed food is efficient, cheap, and widely available while being nutritionally deficient and physiologically disruptive, modern LED lighting is efficient, cheap, and widely available while being spectrally deficient and biologically disruptive.

We are chronically deficient in red and near infrared wavelengths. And we are chronically overexposed to short-wavelength blue light at times and intensities our biology did not evolve to handle.

Dr. Dominic Jeffrey, the researcher whose work on red light and insulin sensitivity I describe in our metabolic health post, made a statement about the public health implications of chronic LED overexposure that I think deserves serious attention. He suggested the scale of potential harm is in the same realm as the asbestos crisis. That comparison is intended to provoke: to make people stop and actually assess what they are being bathed in for 16 hours a day, every day, for their entire lives.

The question that remains open, and that makes deliberate red light exposure so compelling, is whether a regular practice of red and near infrared exposure can compensate for the chronic red deficiency of the modern light environment.

How Your Eyes Communicate with Your Brain About Light

This is not just about skin and mitochondria. Your eyes contain specialized photoreceptors called melanopsin receptors whose sole function is to report to your brain what kind of light is present, at what intensity, as a proxy for what time of day it is.

This information directly governs your cortisol rhythm. Cortisol gets a bad reputation as a stress hormone, but it is also the primary signal for activation, focus, and peak physical performance. The morning cortisol awakening response, a spike in cortisol in the first 30 to 60 minutes after waking, is one of the most important determinants of daily energy, mood, and cognitive performance. Its timing and magnitude are largely set by what your melanopsin receptors see in the first hour after waking.

Short-wavelength (blue-heavy) light in the morning powerfully activates the melanopsin system and sets the cortisol-activation cascade. Long-wavelength (red-heavy) light in the evening tells the melanopsin system that sunset is occurring, preparing the body for rest and melatonin release.

When you wake up and stare at a phone or computer screen in blue-rich LED light before ever going outside, you are sending your melanopsin system a very loud, very clear signal: it is midday. Your cortisol and circadian systems calibrate accordingly. When you sit under blue-heavy LED lights at 10 pm, you are sending the same signal, suppressing melatonin and disrupting sleep architecture.

This is not a minor disruption. Circadian rhythm disruption is associated with impaired immune function, metabolic dysregulation, cognitive decline, mood disorders, and increased cancer risk. The light environment is not peripheral to these outcomes. It is causal.

The Ultraviolet Question: Why the Sun is Not Simply the Enemy

There has been a decades-long campaign in dermatology to minimize sun exposure in all its forms. I understand where this comes from: dermatologists see the consequences of UV damage daily, a sampling bias that makes the sun look uniformly dangerous.

The wavelengths of sunlight that cause DNA damage and skin cancer are ultraviolet: UVA, UVB, and UVC. These are high-energy, short-wavelength, ionizing forms of radiation. They interact with DNA in ways that cause mutations and are legitimately linked to photoaging and skin cancer.

But they are a small slice of the sun's total output. The red and near infrared wavelengths that make up the majority of the sun's spectrum, especially at dawn and dusk, are not ionizing, do not damage DNA, and are actively beneficial through the mitochondrial mechanisms described throughout this series.

A nuanced relationship with sunlight looks like this: morning and evening outdoor exposure when the spectrum is red-heavy, protection during peak UV hours in the middle of the day, and understanding that avoiding the sun entirely deprives you of some of the most powerful biological inputs available to you.

At a recent major medical conference, I heard a dermatologist, for what felt like the first time in my professional life, hint on stage at the fact that long-wavelength sunlight is good for us. That is progress.

What a Healthy Light Diet Looks Like

The goal is not to add red light therapy and leave everything else unchanged. It is to restore something closer to the spectral balance your biology was built for. Here is what that looks like in practice:

Morning outdoor exposure. Even five to fifteen minutes outside in the first hour after waking, when long-wavelength light is dominant, sets the melanopsin and cortisol systems. On cloudy days this still matters: the light intensity outdoors even under cloud cover is orders of magnitude higher than any indoor environment.

Circadian-friendly home lighting. Lighting systems that shift color temperature throughout the day, warmer and redder in the evening, cooler in the morning, more closely approximate the natural light cycle. My home uses such a system. By evening, it looks essentially like firelight inside.

Deliberate red light exposure. This is where devices come in. A morning red light session before noon compensates for the red deficiency of indoor LED environments and layers the mitochondrial benefits described in this series onto the circadian benefits of morning light. See How to Choose a Red Light Therapy Device for the practical application.

Reducing evening blue light. Blue-blocking glasses in the evening, reducing screen exposure in the two hours before bed, and using warm incandescent-spectrum lighting after sunset all reduce the circadian disruption of evening LED exposure.

Strategic use of bright light on high-performance days. On surgical days, I use a 10,000-lux full-spectrum lamp in the morning to activate my melanopsin and cortisol systems when natural sunlight is not available. The Pacific Northwest in winter provides very little outdoor light before a 7 AM surgery start time for me.

For Families

Everything I have described applies to children, and perhaps more acutely. Children's eyes transmit more blue light than adult eyes, making them more susceptible to the circadian disruption of evening screen use. They are also in developmental periods where circadian rhythm integrity matters enormously for learning, mood, growth, and immune function.

In my household, my children understand the basics of light diet. They know what I call "junk light" is and why it matters. They join me in the sauna with red light panels. We make an effort to be outside early in the morning and at sunset. We use warm lighting after dark and manage screen time in the evening with the biology in mind, not just the parenting conventional wisdom.

This is one of the highest-leverage things a family can do for collective metabolic and neurological health, and it costs almost nothing beyond awareness.

Frequently Asked Questions

What is junk light?

Junk light is a term I made up for the spectrally deficient output of modern LED lighting: heavy in short-wavelength blue light, minimal to absent in red and near infrared wavelengths. By analogy with highly processed food, it is an efficient and widely available substitute for the natural light environment that lacks the biological inputs our cells actually need. Chronic exposure to junk light at the expense of natural full-spectrum light is associated with circadian disruption, metabolic dysregulation, and deficiency in the red and near infrared inputs that drive mitochondrial health.

Is blue light really bad for you?

Blue light is not inherently bad. It is a necessary part of the natural light spectrum and plays an important role in circadian activation in the morning. The problem is chronic overexposure to blue-heavy artificial light at times and intensities that are biologically incoherent: staring at blue-rich screens at 11 pm, working under blue-heavy LED office lights for 10 hours a day, and having minimal exposure to the red and near infrared wavelengths that balance the spectrum. The issue is imbalance, not the wavelength itself.

Why is morning sunlight so important?

The eye's melanopsin receptors are most sensitive to light signals in the morning. Outdoor light in the first hour after waking, even on overcast days, sets the circadian cortisol rhythm that determines energy, focus, and performance for the day. Morning outdoor light also delivers the longer wavelengths of early-day sunlight that support mitochondrial function. The combination of circadian activation and photobiomodulatory benefit from morning natural light is one of the highest-leverage, lowest-cost health interventions available.

What is a circadian lighting system?

A circadian lighting system adjusts the color temperature and intensity of home or office lighting throughout the day to more closely match the natural light cycle. In the morning, light is cooler and brighter to support cortisol activation. In the evening, light shifts warmer and dimmer, resembling firelight, to support melatonin production and sleep readiness. Smart bulb systems like those from Philips Hue, LIFX, and others can be programmed to follow this pattern automatically. The result is a light environment that works with your biology rather than against it.

Should I be concerned about LED lights at home?

Aware, rather than alarmed. The aggregate effect of spending most waking hours under blue-heavy LED lighting with minimal red and near infrared exposure is a genuine biological stressor. Making changes to your home lighting, particularly in the evening, toward warmer spectrum bulbs is a practical and affordable intervention. Adding deliberate red light exposure in the morning to compensate for the spectral deficiency of indoor environments adds the mitochondrial benefits of photobiomodulation. Neither requires major expense or lifestyle disruption.

Does watching the sunrise actually do anything physiologically?

Yes, meaningfully. Sunrise light is spectrally distinct from midday light, heavily weighted toward red and near infrared wavelengths. Getting these wavelengths on the skin and eyes in the morning triggers melanopsin-mediated cortisol activation, provides direct photobiomodulatory mitochondrial stimulation, and sets the circadian rhythm for the day. Multiple researchers in the photobiology field advocate for sunrise viewing specifically as a health practice, distinct from general outdoor time, because of the unique spectral composition of low-angle morning sunlight.

Continue reading our red light series:

Dr. Cameron Chesnut is a facial plastic surgeon and founder of Clinic 5C. Views expressed are his own and are not affiliated with the University of Washington School of Medicine. This content is for educational purposes only and is not individual medical advice.

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