HARMFUL BLUE LIGHT
Harmful blue light (formerly also called Blue-light hazard), is an effect that causes short-term and long-term damage to the pigment cells of the retinal epithelium (RPE cells) as well as retinal photoreceptors . In the long term, HBL has a cumulative effect and a probable causal relationship to higher incidence of age-related macular degeneration (AMD). The range of wavelengths causing HBL is defined by the International Commission on Illumination (CIE) as a fucntion in the range 380-500 nm (Figure 2 in ) with the strongest negative phototoxic effect observed in the range of 415-455 nm [1,3-6] as these wavelengths generate the highest amount of damaging free radicals (reactive oxygen species, ROS) on the retina of the eye. These radicals contribute to cellular aging and more research suggests their role in the formation of AMD 
Description of Figure 1: Curve 1: Area stimulating oxidative stress damaging the mitochondria of A2E-loaded retinal cells by the formation of peroxides and free radicals (ROS) . Curve 2: HBL function according to CIE . Curve 3 represents the absorption spectrum of A2E , Curve 4 CIE represents the luminosity function v(ƛ) and Curve 5 epresents stimulation of RNA synthesis rate – the absorption spectrum of human mitochondria (more in the photobiomodulation effect section) . Graph adapted from .
The mechanism of the damaging effect on the retina is through the formation of peroxides and free radicals (reactive oxygen species, ROS), which are formed after excitation of the photosensitive retinal component A2E (other pigments may be involved too) by the HBL wavelengths of the visible spectrum. A2E a component of lipofuscin pigment, the pigment of ageing, which accumulates in retinal cells as a decomposition product. ROS induces death of RPE cells, which are responsible for the regeneration of rod and cone photoreceptors. Their decomposition thus damages the life of photoreceptors and, in addition, generates another lipofuscin that contains A2E, which in turn generates more ROS after excitation – this thus creates a destructive cyclical cascade . Intracellular lipofuscin deposits also stimulate the formation of extracellular yellow fluorescent pigment deposits (called drusen) – a typical symptom of AMD. Therefore, lens filtration of the HBL region has a therapeutic effect in people with various retinal diseases, including AMD .
Harmful Blue Light (HBL) defines the most damaging region of the visible spectrum for the retina in the range of 415-455 nm (the region of violet and partially blue wavelengths). These wavelengths could be a risk factor for a higher incidence of age-related macular degeneration. New research suggests that this negative effect of HBL can be counterbalanced by the photobiomodulation (PBM) effect (point 4).
- Unfortunately, a fluorescent lamp always emits energy in the whole of the HBL region – violet and neighbouring blue wavelengths.
- A conventional LED light source has a typical maximum limit at 450 nm (not below), but sources with more damaging violet peak at 420 nm are also emerging.
- The Spectrasol LED light source also emits light at 450 nm, but unlike the conventional LED light source, this energy is not a peak energy (it is not concentrated), but is part of the full continuous spectrum emission similar to sunlight – moreover, any negative effect is compensated for with the protective radiation in the photobiomodulation region, again akin to sunlight.
- The sun at noon emits continuously in the entire HBL region, as well as in the damaging UV region, but on the other hand also in the entire photobiomodulation region.
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