Blue light is part of the visible spectrum with wavelengths between 380 and 500 nanometers. It is the most energetic portion of visible light, and due to its intensity and scattering in the atmosphere, the sky appears blue.

In nature, the main source of blue light is the Sun. However, modern lifestyles have introduced new sources of artificially produced blue light, such as phone, computer, and television screens, as well as LED lighting. The problem arises when we are exposed to this light in the evening, as it directly affects our circadian rhythm the internal biological clock that regulates sleep, wakefulness, and hormones.

Blue light activates special cells in the eye that contain melanopsin. These cells send signals to the suprachiasmatic nucleus in the hypothalamus a part of the brain that controls melatonin production, the sleep hormone. When you are exposed to screens in the evening, your brain receives a false message: “It’s still daytime.” This leads to difficulty falling asleep, shorter sleep duration, reduced concentration, and a disrupted biological rhythm.

Although it sounds dangerous, blue light is not an enemy. Moderate exposure during the day helps increase alertness, focus, and mood. In medicine, it is also used for therapeutic purposes and, when applied correctly, can provide benefits. Blue light phototherapy breaks down bilirubin in newborns with jaundice. Low-dose light photobiomodulation stimulates tissue regeneration and has antibacterial effects.

Blue light is an inevitable part of modern life, contributing to increased energy, focus, and enhanced visual clarity. The problem arises with exposure to artificial blue light in the evening, which alters the circadian rhythm and, over time, can disrupt sleep and eye health. The solution is not to avoid light, but to maintain a balance between natural and artificial sources, day and night, activity and rest.