Interior Lighting, a Challenge for Yesterday's and Today's Engineering

There were periods when, apparently, in the interior lighting, things seemed to be resolved, clarified and nothing was necessary to investigate. Such was the long period of incandescent lamps and fluorescent lamps, burdened by the erroneous perception and understanding of Kruithoff's curve, which was contested only after half a century. The compact fluorescent lamp, which appeared next, seemed to represent a solution for energy efficiency and interior comfort. However, the negative effects of the blue components in the spectrum have been noticed. The continuous evolution of LEDs has once again changed the paradigm, and it has made necessary to continuously observe and research the physiological and psychological effects of exposure to artificial light. The main effect is the disturbance of the circadian cycle, which depends on the secretion of a specific hormone. The problem with this hormone, namely melatonin, is that it has physiological effects in the area where certain types of cancer occur, but also psychological ones, in the direction of mood, alertness, and concentration. The aim of this paper is to make an in-depth review of the existing literature on the subject of the influence of artificial lighting on human activities, with a focus on the influence of the spectral composition of LED lighting sources on learning activities in schools.