**6. Results and Discussions**

Throughout this review, we have examined works by scientists who are experts in different branches of knowledge related to humans. These studies confirm that human beings are designed to carry out all their physiological and cognitive activities during the day and to rest at night. Our civilization has changed the natural light–dark cycle that humans experience. Researchers have expressed concern over electric lighting as a potential disruptor of the natural light–dark cycle [16].

Some articles [10,59,113] have stated that LED lights are dangerous because they emit much more blue light than other types of lights and the sun. In studies on the development of LEDs, several examples of technical publications have refuted the theory that new light sources radiate more blue light than traditional sources (rather the opposite), including the sun. New LED-type light sources do not necessarily produce a higher percentage of blue light than traditional light sources (mercury vapor lamps, halogens, etc).

In addition, under normal working conditions, in accordance with current lighting legislation, around 500 lx should be received at one's workplace, regardless of the type of luminaire used.

If we compare the illuminance emitted by lights against those of solar irradiance, we find that a cloudy day in the northern hemisphere will produce about 3000 lx; about 50,000 lx on a sunny summer day in Spain; and about 100,000 lx in the tropics. Thus, we can conclude that the possible risk of blue light on the retina under general lighting indoors is low to very low, even if one uses cold color temperatures as general lighting.

The neurons responsible for the melatonin, serotonin balance (ipRGCs), are sensitive to light from UVA to red, with their peak in blue. By absorbing light at the beginning of the day, melatonin is eliminated and replaced by serotonin [59]. Within the range of the visible spectrum, the most abundant energy we receive from the sun is blue, and its peak is approximately 480 nm. This is, therefore, the peak of the maximum sensitivity of melatonin. Beings who are active during the day have evolved by adapting to sunlight [114].

Since the discovery of these neurons 25 years ago, the scientific world has not stopped discovering evidence of the synchronization of our organs, and even our individual cells, with the light and dark cycles of nature. These discoveries are considered so important for the scientific world that the 2017 Nobel Prize in Physiology and Medicine was awarded jointly to Jeffrey C. Hall, Michael Rosbash, and Michael W. Young for their discoveries of the molecular mechanisms underlying the control of circadian rhythms.

Artificial light has facilitated great advances in many fields, but it can also pose a risk as it can alter the natural cycles of sleep and wakefulness, in many cases reducing the hours of sleep by people being able to continue to carry out activities during the night period. An alteration of sleep can pose a risk to health, leading to chronodisruption. Chronodisruption is an alteration of the internal temporal order of physiological, biological, and behavioral rhythms. If it becomes chronic, asynchrony, advancement, or retardation of the peripheral clocks may occur [17].

Epidemiological studies show that chronodisruption is associated with an increased incidence of metabolic syndrome, cardiovascular disease, cognitive and emotional disorders, premature aging, and some cancers such as breast, prostate, and colorectal cancer, as well as the worsening of pre-existing pathologies.

The scientific community has shown, with multiple studies, that humans need biorhythms to receive sufficient amounts of light in the blue range during the day but in a different proportion depending on the time of day. Erren and Reiter define correct lighting as photohygiene. This factor is already considered so important for health that the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) included shift work as a cancer-inducing factor in 2010.

Many articles recommend that the reception of artificial light should be as close as possible to daylight. It should be more intense with a higher proportion of blue, with a maximum value at mid-morning, which should then decrease in intensity and quantity, mainly in its proportion of blue. For more than ten years, correct or incorrect lighting has been associated with the good or bad physical and psychological conditions of people [17].

Increasingly more scientists are advocating the study and development of luminaires that are more in line with sunlight [21], and there is a call for interior lighting that not only differs throughout the day, but also differs depending on the seasons based on the response to their cumulative absorption, i.e., there should be more intense irradiance in public spaces (including schools) in autumn and winter and less in spring and summer [39,40].

Experiments have been carried out on patients with dementia and other neuropsychiatric pathologies where researchers improved the symptoms of their illnesses by receiving light closer to daylight. This light was more intense and featured a greater amount of light in the blue range than that which they received in the centers where they reside [31].

Notably, Glickman et al. [20] observed that, although it was initially thought that an illuminance of 2500 lx is necessary to suppress nocturnal melatonin in humans, under certain conditions, values as low as 10 lx [114], and possibly 1 lx or less, can suppress melatonin in humans. This would support the recommendation to sleep in complete darkness since, if we have any lights on, that very small amount of light could pass through our eyelids.

The current majority of studies states that the minimum amount of light that we receive from 9:00–10:00 p.m. will delay the transition from serotonin to melatonin and, therefore, delay the process of rest that is essential for health. Moreover, the sudden reception of low-intensity light delays the process since this light is not received for at least 40 min [27]. If these disorders persist over time, chronodisruption and undesirable cortisol levels may occur. Scientists have related this disorder to metabolic syndrome, cancer, obesity, diabetes, cardiovascular disease, and cognitive and affective disorders.

The accredited test laboratory FUTTEC measured the amount of blue light emitted by various electronic equipment used by children and adolescents in 2014 and 2019. The results show that the irradiance in the blue range of these devices (at the distance they are commonly used) is between 1000 and 10,000 times lower than what we can receive at the same time from the sun on a spring day with a UVI of 6. Compared to a day with a UVI of 9, this amount would be up to 30% higher on a spring day. Based on these results, it is not considered plausible that this equipment is harmful to the retina, as our eyes can survive 1000 to 10,000 times more light than they receive from these devices from the sun.

Yoshimura et al. [115], in their study on the use of mobile phones among 23 nursing students, found the peak of light of the mobile phones at 453 nm, and the illuminance in the seated measurements were from 25.3 to 42.6 lx; lying down, these values ranged from 50.5 to 80.4 lx. The authors logically note that this amount of light is not likely harmful to the eye (as per other studies) but can affect circadian cycles and sleep quality.

Escofet and Bará [55] studied the emissions of two computer screens and two smartphones with irradiance results from the computers of 4 <sup>×</sup> <sup>10</sup>−<sup>3</sup> <sup>W</sup>/m2 around 450 nm and 6–7 <sup>×</sup> <sup>10</sup>−<sup>4</sup> <sup>W</sup>/m<sup>2</sup> from the two smartphones. The authors recommend the use of filters to protect from such irradiation. This irradiance, however, is between thousands and tens of thousands of times lower than the irradiance we receive from the sun.

An important issue for optometrists is that if we remove the part of the spectrum that we can most comfortably accommodate at close distances, as explained in the introduction to this paper, we would have to make more accommodation efforts and would require greater light intensity to do the same job. Would that not be more counterproductive than removing a small percentage of blue?

The results of the measurements and scientific publications show that the composition of light used for indoor lighting can influence the balance between serotonin and melatonin and therefore, our circadian cycles.

• Analysis of the possible negative effects of blue light from electronic devices on the eyes of adolescents

Various news media have reaffirmed the results (according to scientific studies) that suggest the damaging effects of blue light emitted by sources of artificial light on the retina (both LED lights and computers and mobile phones). These results are supported by published articles that correlate a greater exposure to light emitted by LEDs with a greater absorption of light in the blue range which, as a consequence, can accelerate the development of cataracts, pose a greater risk of damage to the retina, and, therefore, increase the prevalence of age-related macular degeneration (AMD). Many companies in the optical sector offer filters that absorb much of the blue light emitted by electronic devices to protect children and adolescents from this hypothetical risk.

After observing the prevalence of this concern, a search was made for scientific articles that corroborate this concern. The aim was to find an article showing the results of the irradiation of cell cultures or exposure to guinea pigs via the light actually emitted by this electronic equipment.

Notably, all the studies to date that note the possible damage from blue light in living tissue, especially the retina, have been carried out on cultures or living animals using monochromatic LED sources (emitting only in the most oxidizing part of the blue spectrum), with significantly higher irradiance levels than those actually emitted by electronic equipment.

Moreover, the experimental animals used include mice and rabbits, which are nocturnal animals whose visual systems are much more sensitive to light than those of humans, without any kind of algorithm or objective method to transpose these results into the possible effects on humans.

As a result, we believe that it is not possible to directly associate ICT's emissions with the possible real risks in the retinas of adolescents.

• Studies on the effects of artificial light sources on adolescents

There is an increasing number of publications by researchers (mainly from Asian countries) that relate low indoor lighting and natural light to the increase in myopia among children and adolescents worldwide, which in some countries, such as Singapore, involves more than 90% of children. The specific causes are unknown. No article has provided conclusive results [112]. This pandemic remains a challenge for the scientific community.

The dependence and addiction due to the indiscriminate use of mobile phones by children and adolescents all over the world already have attention within the scientific community, (e.g., nomophobia). This is a different problem from chronodisruption described above.

There is talk of a greater risk in children than in adults due to physiological reasons such as increased nerve conductivity and unwanted effects such as headache, dizziness, sleep problems, insomnia, dependence syndrome, and mental or behavioral disorders [56–59,67,115].

According to the results of the INE 2017, the percentage of minors who use a mobile phone in Spain reached 94% by the age of 15, making it a health priority to provide relevant information and control the use of ICT by adolescents [71].

• Existing and developing regulations for the non-visual effects of light absorbed through our eyes

The authorities in the European Community, through the CIE, and internationally through the International Organization for Standardization (ISO), have been sensitive to the concerns of the scientific community, and groups with experts in different fields have been increasingly established to study the non-visual effects of light.

In the development of this study, the work of the European Community was broken down as a Green Paper published in 2011. When this document was published, the scientific community was not yet aware of the technological revolution of the new LED lighting systems to come, especially from the perspective of their possible influence on people's states of mind.

European bodies studying health risks, such as the SCENIHR and the CIE from 2012 onwards, have gradually entered into the exciting study of this new field of science.

Concern over ICT irradiance is growing. This concern is reflected by the proposal produced at the end of 2018 for a group of experts from the CIE and ISO to jointly create a new document (integrative lighting) to use this research for the development of standards that define the composition of light in each area in which it will be used.
