Light is a form of electromagnetic radiation that carries energy.

It has a dual nature, behaving both as a wave and as a particle. As a wave, light exhibits phenomena such as diffraction, interference, and polarization. As a particle, in the form of photons, it participates in processes like the photoelectric effect, photon absorption, and photon emission.

Light is also defined by two key properties: its frequency (f), which represents the number of oscillations per second and is measured in Hertz (Hz), and its wavelength (λ), which is the distance between successive wave crests. These two properties are interconnected through the fundamental equation c = λ · f, where c is the speed of light.

The main cue for our clocks is light. Special light-sensitive proteins in our eyes and skin, called opsins, and molecules within cells that absorb photons to trigger cellular processes (such as Chromophores) detect different wavelengths of light and relay this information to the brain.

The length of the wavelength affects how light penetrates:

• Short wavelengths (blue and violet) are high-energy and scatter more in the atmosphere. They penetrate less deeply into surfaces but strongly influence the SCN and circadian signaling.
• Long wavelengths (red, orange) are lower-energy, penetrate deeper, and dominate during sunrise and sunset when the sun is at a low angle.

Because the Earth rotates and tilts on its axis, the angle of sunlight changes throughout the day:

• Morning (sunrise, low angle): UV missing, blue light is still present but mixed with red/orange, giving a gentle wake-up signal.
• Midday (sun overhead, high angle): UV rises, Blue light present and the without missing the red component (almost 50% of the spectrum)
• Evening (sunset, low angle again): Blue light fades, red and orange dominate.

This shifting spectral composition from short, high-energy UV and blue in the middle of the day to long, red wavelengths at sunrise and sunset is what keeps our master clock and peripheral clocks in sync with the environment. Our body evolved to anticipate these changes, adjusting hormone release, metabolism, and energy use according to the natural light spectrum.

This is how beautifully complex our circadian biology is, every system in our body, hormones, neurotransmitters, metabolism, sleep, even tissue structure runs on the rhythm set by our environmental input (light, darkness, temperature, and food timing... ).

At sunrise dopamine and cortisol begins to rise to mobilize energy and alertness, enhance mood, motivation, and mitochondrial priming. Serotonin precursors are triggered, histamine is disinhibited, satiety is decreased, hunger rises. TSH peak to anticipate metabolic demand. ACTH is cleaved from POMC. Cortisol and infrared light work on collagen and water to change tissue structure, literally waking the body by zipping and unzipping collagen, shifting charge and tensegrity.

Morning sunlight not only boosts mitochondrial energy production but also activates the raw materials we need to build dopamine, serotonin, and other neurotransmitters. As the day progresses, UVA light supports sex hormone pulses, thyroid activity, nitric oxide release supporting vasodilation, and mitochondrial biogenesis, regulating blood pressure and controlling skin chemistry, Serotonin is made, dopamine production is enhanced, Endorphins for mood and pain relief are released. while UVB shifts the body toward vitamin D production and glucose metabolism.

As light fades, the reverse unfolds, serotonin is converted into melatonin in darkness, guiding us into deep sleep cycles where the glymphatic system clears waste, tissues repair, and growth hormone surges. Magnetism dominates at night, condensing matter and restoring order, while melatonin acts as the security guard, and repairman of the brain and body.

Blue light is a type of light with a wavelength range between 400-500 nanometers, which is part of the visible light spectrum.

It is a short-wavelength, high-energy component of sunlight that powerfully influences our circadian rhythm, alertness, and mood. It primarily interacts with opsins in our eyes and tissues to communicate “daytime” signals to our body.

In a circadian context during the day, blue light is NECESSARY, it boosts alertness, supports cognitive function, and regulates circadian rhythms by suppressing melatonin and stimulates cortisol production.

Unlike the sun’s full spectrum with an even distribution of all colors, most modern devices, screens, and LED lighting emit concentrated amounts of blue light, lacking the balancing red color that occurs naturally.

Problems arise especially when blue light is encountered after sunset.
Evening exposure, tricks the brain into thinking it is still daytime, delaying melatonin release and disrupting the natural sleep-wake cycle. This interference prevents deep, restorative sleep, compromising mitochondrial repair, energy production, immune function, and hormone regulation. Chronic exposure can increase risks for metabolic issues, mood disorders, and even long-term conditions like obesity, cancer, and cognitive decline.
That’s why blocking artificial blue light matters, it helps protect sleep by preserving melatonin production, optimizes circadian hormone cycles, reduces eye strain and retinal damage, and maintains long-term health.