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Blockers, absorbers, and windows

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Ultraviolet absorbers are molecules used in organic materials (polymers, paints, etc.) to absorb UV radiation to reduce the UV degradation (photo-oxidation) of a material. The absorbers can themselves degrade over time, so monitoring of absorber levels in weathered materials is necessary. In sunscreen, ingredients that absorb UVA/UVB rays, such as avobenzone, oxybenzone and octyl methoxycinnamate, are organic chemical absorbers or "blockers". They are contrasted with inorganic absorbers/"blockers" of UV radiation such as carbon black, titanium dioxide, and zinc oxide. For clothing, the ultraviolet protection factor (UPF) represents the ratio of sunburn-causing UV without and with the protection of the fabric, similar to sun protection factor (SPF) ratings for sunscreen. citation needed Standard summer fabrics have UPFs around 6, which means that about 20% of UV will pass through. citation needed Suspended nanoparticles in stained glass prevent UV rays from causing...
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Visibility

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Ultraviolet rays are invisible to most humans. The lens of the human eye blocks most radiation in the wavelength range of 300–400 nm; shorter wavelengths are blocked by the cornea. Humans also lack color receptor adaptations for ultraviolet rays. Nevertheless, the photoreceptors of the retina are sensitive to near-UV, and people lacking a lens (a condition known as aphakia) perceive near-UV as whitish-blue or whitish-violet. Under some conditions, children and young adults can see ultraviolet down to wavelengths around 310 nm. Near-UV radiation is visible to insects, some mammals, and birds. Small birds have a fourth color receptor for ultraviolet rays; this gives birds "true" UV vision.
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Subtypes

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The electromagnetic spectrum of ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into a number of ranges recommended by the ISO standard ISO-21348: Name Abbreviation Wavelength (nm) Photon energy (eV, aJ) Notes/alternative names Ultraviolet C UVC 100–280 4.43–12.4, 0.710–1.987 Short-wave, germicidal, completely absorbed by the ozone layer and atmosphere: hard UV. Ultraviolet B UVB 280–315 3.94–4.43, 0.631–0.710 Medium-wave, mostly absorbed by the ozone layer: intermediate UV; Dorno  de radiation. Ultraviolet A UVA 315–400 3.10–3.94, 0.497–0.631 Long-wave, black light, not absorbed by the ozone layer: soft UV. Hydrogen Lyman-alpha H Lyman-α 121–122 10.16–10.25, 1.628–1.642 Spectral line at 121.6 nm, 10.20   eV. Ionizing radiation at shorter wavelengths. Far ultraviolet FUV 122–200 6.20–10.16, 0.993–1.628 Middle ultraviolet MUV 200–300 4.13–6.20, 0.662–0.993 Near ultraviolet NUV 300–400 3.10–4.1...
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