Spectral Power Distribution of Artificial Light Sources Leading to Alpha Opic Influence on Humans

The paper presents an investigation on the possibilities to introduce LED indoor luminaires, that are not only efficient but also have a significant impact on the natural cyclic processes in the human body. A combination of spectral power distributions of existing LEDs is made, so that composite spectra obtained positively influences the retinal cells in the human body and leads to increase in alertness and productivity. The alpha-opic influence of the new spectral power distributions is estimated, and based on the results some important conclusions are made. With the emergence of LEDs as most efficient light source and the tendency for replacement of all the existing sources of light with their LED alternatives comes the question whether this replacement leads only to reduction in the consumption of electrical energy for lighting or also has other advantages, connected to the influence of the solid state lighting on the human body. In the natural evolution of life, human beings are used to daylight and have been using it until now as a free and very powerful light source. The illuminance levels in the open on an average sunny day in Bulgaria exceed 100000 lux and go under 1000 lux at cloudy skies, which levels are significantly higher, than those reached in indoor spaces [1]. Nevertheless, what the weather is, however, during the day there is always daylight and this daylight influences and dictates the cyclic processes in the human body. Nowadays, because of the great variety of artificial light sources that exist, light is available all the time. And here arises the question whether the illuminance levels, prescribed by the standard for lighting of indoor workplaces EN 12464-1 [2] that are significantly lower than those in the open can influence the circadian rhythms and if yes to what extent, compared to the natural daylight. The lower illuminance levels indoors are not the only consideration, taken into account when such an estimation is made. The more important question is whether the spectral power distribution of the artificial light sources, that is completely different from that of the daylight and depend on the principle of light generation, can lead to stimulation of the retinal cells and lead to realization of the non-visual effects of light, the way that it leads to vision. A lot of research is carried out on these topics nowadays, but a straightforward decision is yet to be reached. And the most important questions to be answered are two. The first is whether the light levels indoors are enough to make the central master clock, which in humans is the suprachiasmatic nuclei (SCN) operate the same way as it does when it is submitted to daylight. Although the light, emitted by all the artificial light sources used for general lighting is visually intercepted as “white” in the retina of the eye, their chronobiological influence on circadian rhythms is not equal and its influence on hormones’ secretion and the human psychology differs to a great extent. So, the second important question is whether artificial light spectral power distribution with non-visual influence close to that of the natural light can be reached. Until recently, it was considered that rods and cones are the photoreceptors convicting the visual process and the retinal ganglion cells with their photopigment melanopsin are responsible for the circadian rhythms, alertness, and melatonin suppression. The most recent research findings, however, forward new evidence that these ganglion cells (the so-called photosensitive retinal ganglion cells) also contribute to visual perception modulation and the cones influence to a sudden extend the non-visual effects of light and the length of the exposure to light [3].