• Problems with poor lighting in classrooms

Studies on classroom lighting in this century and last century have reflected the widespread concern around obtaining the best possible lighting for children. We found an abundance of publications that discuss the unwanted effects on children of having classrooms that are either under-lit or over-lit [79,81,82]. The problems of inadequate illumination can be divided into temporary physiological problems of the visual system, psychological problems, and permanent problems of the visual system. For many years, there have been publications on possible temporary physiological disorders of the visual system, such as glare, headache, and/or fixation problems [81,82,85,87]. Some authors have realized, from the results of their studies, that poor lighting, whether natural or artificial, has notable negative effects on children's performance and mood [84,85].

The current pandemic of child myopia is an issue of global concern, but it is especially of concern in Asian countries, where it is most prevalent. One of the theories proposed by scientists who study this problem is that this increase in child myopia may be due to the short amount of time that children are outdoors receiving natural light. The recommendation for indoor lighting is between 300 and 500 lx, while outdoor light even on a cloudy day is tens of thousands of lx [90–94,116].

Figueira et al. [116] show that 1-h and 2-h exposure to light from self-luminous devices significantly suppressed melatonin by approximately 23% and 38%, respectively. The authors' previous studies suggest that adolescents may be more sensitive to light than other populations.

• Effects of classroom lighting on student performance

In 1992, the researchers Kuller and Lindsten [102] published an article in which they associated insufficient light levels with inadequate levels of hormones, leading to negative effects on children's behavior, and recommended that there be no classrooms built without natural lighting. At the time of their study, the relationship between light and the pineal gland and biorhythms was still unknown. Later studies found a relationship between correct artificial lighting or a combination of natural and artificial light and better performance of students in the classroom [98–101].

The influence of light on people's moods remains a subject of study today, throughout the scientific world. Official and scientific bodies involved in the world of lighting, such as the International Committee on Illumination (CIE) and the Lighting Research Center, have been researching and publishing studies for decades relating to the possible effect of lighting on the moods of students in the classroom, and the influence of this on their learning ability and their performance [102,109–112,116].
