Human eyes will hardly see wavelengths below 400nm.
Erythemal (sunburn) occurs in the UVB range (280nm – 315nm).
Germicidal occurs UVC range (200nm - 280nm).
In the past, UVA (315nm - 400nm) was considered not harmful or less harmful, but today it is known it can contribute to skin cancer via indirect DNA damage . UVA can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA. Accordingly the DNA damage caused indirectly to skin by UVA consists mostly of single-strand breaks in DNA,
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