Blue light hazard
Blue-light hazard, or so-called harmful blue light, 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, BLH has a cumulative effect and a probable causal relationship to higher incidence of age-related macular degeneration (AMD). The range of wavelengths causing BLH 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: BLH 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 .
Summary and comparison of the Blue-light hazard effect of light sources
Blue-light hazard (BLH) 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 BLH can be counterbalanced by the photobiomodulation (PBM) effect (point 4).
- Unfortunately, a fluorescent lamp always emits energy in the whole of the BLH 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 BLH region, as well as in the damaging UV region, but on the other hand also in the entire photobiomodulation region.