We often think about light like a lamp: something you switch on when it gets dark. For the body, however, light is much more – it is a biological operating code. A language that every cell understands and responds to, long before we consciously notice anything.

Light is not just brightness. Each wavelength carries its own message. In the morning, the cool, blue light of the sun sends the signal: wake up, release cortisol, become active. In the evening, when the light becomes warmer and redder, the body begins producing melatonin – the timekeeper for recovery, repair, and sleep.

This interplay is no luxury; it is deeply embedded in our biology. Over millions of years, our internal clock – the circadian rhythm – has synchronized with the natural course of daylight. It not only regulates sleep and wake times, but also influences metabolism, hormone production, immune defense, and even the efficiency of cellular repair.

However, the daily routine of many people has thrown this precise calibration off balance. LED lamps, screens, and smartphone displays emit light in the evening that makes the body believe it is still daytime. At the same time, many people miss the powerful morning impulse of sunlight. The result: our inner timekeeping loses its sharpness, important processes stumble – often without us realizing the connection to light.

Remarkably, light does not only work through the eyes. Certain wavelengths – especially red and near-infrared light – penetrate deep into tissue. There, they reach the mitochondria, the power plants of our cells. These respond as if receiving an energy boost: they produce more ATP, the universal cellular energy, and initiate repair and anti-inflammatory processes.

In this sense, light is not merely an external stimulus, but a direct dialogue with our biochemistry. The real question, therefore, is not whether we react to light, but how consciously we steer this reaction – and which opportunities we leave unused.

In the next part of this series, we will look exactly at that: the targeted use of red and infrared light – photobiomodulation – as a key to actively speaking this biological language.