The adjustment factor for many organic processes in human beings is a change of the melatonin concentration in the blood. Melatonin is a hormone produced in the pineal gland in the central brain. The melatonin level is regarded as a significant indicator for human actionability, as an indicator for the need to sleep and for the biological clock.

The melatonin level is directly controlled by the light energy incident on the retina. Low amounts of light means a high release of melatonin and thus an elevated need for sleep. The body temperature sinks. Conversely, light suppresses melatonin production and increases vitality and alertness.

Studies with shift workers showed that a provision of high illuminance and neutral-white or bright-white light colour lowers the melatonin level and decreases the need for sleep and thus significantly reduces fatigue, lack of concentration and working errors during night shifts.

However, it is important to note that in terms of health, particularly in shift operations, circadian rhythm support should be targeted (see chapter "Human Centric Lighting"). Working errors and accident risks can also prevented here e.g. by facilitating the visual task through increased illuminance in the warm-white spectral range. Melanopically effective blue portions in the light are not required. This way, the inner clock of shift workers is "thrown off beat" as little as possible.