Advanced UV for Life
Natural UV Radiation
It is invisible, silent – and yet omnipresent: the sun’s ultraviolet radiation, or UV radiation for short. As the most energetic part of optical radiation, it covers wavelengths between 100* and 400* nanometers (nm) and plays a crucial role for the environment and health. Although we can neither see nor feel it, it influences our lives daily – from sunbathing to the risk of skin cancer.
* 100 nm is often found as a designation for the lower range of natural UV radiation. In technical contexts, however, the value
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Short-Wave, High-Energy
Natural Ultraviolet Radiation
In the electromagnetic spectrum, UV radiation lies between visible light (approx. 400-750 nm) and ionizing X-rays (X-Ray, <10 nm). Thus, it directly borders the light visible to us. Compared to visible light, UV radiation is short-wavelength and more energetic, which explains its biological effects – both positive and negative.
Natural UV radiation is divided into three main areas:
UV-A radiation (400-315 nm): The longest-waved and least energy-rich UV component, which reaches the Earth’s surface almost unhindered. It penetrates deep into the skin and contributes to skin aging.
UV-B radiation (315-280 nm): More energy-rich than UV-A, mostly filtered by the ozone layer, but up to 10% reaches the Earth’s surface. It is responsible for sunburn and plays a role in vitamin D synthesis.
UV-C radiation (280–100 nm): The most energetic form of UV radiation, which is almost completely absorbed by the Earth’s atmosphere.
A further differentiation of UV ranges is common in technical contexts and especially for artificial UV radiation (see below).
How strongly we are exposed to the sun’s natural UV radiation depends on several factors: geographical location, time of day and year, altitude, and cloud cover play a central role. For instance, UV intensity increases by about ten percent with each kilometer of altitude in mountainous regions. Reflective surfaces such as water, sand, or snow can also intensify the radiation – turning a seemingly harmless walk into a health risk.
Despite its important significance, UV radiation poses risks. It can damage the skin, lead to premature aging, and increase the risk of skin cancer. The eyes are also sensitive – to the point of risking permanent damage. For this reason, UV intensity is monitored worldwide and regularly published in the so-called UV index.
Protection against excessive UV radiation is also our responsibility: sunscreen, protective clothing, headwear, and conscious handling of sun and shade are simple but effective measures. Thus, the invisible radiation does not become an invisible risk – but a force that we can understand and use safely.
(In)Visibility
Ultraviolet radiation
Ultraviolet radiation is invisible to humans. It is correctly no longer referred to as “light” but only as “radiation”. The lens of the human eye – and also artificial lenses, such as those used in operations – block most of the radiation in the near UV range between 300 and 400 nm. Even shorter wavelengths are already intercepted by the cornea (1). Humans also do not have color receptors that specifically react to ultraviolet radiation. Although the photoreceptors of the retina are theoretically sensitive to near UV radiation, the lens does not focus this light, which is why UV lamps appear blurry to the human eye (2). People who lack the lens – for example, after an operation (aphakia) – perceive near UV radiation as whitish-blue or whitish-violet (3).
It’s different for many animals: Numerous bird species, insects, and other vertebrates can perceive ultraviolet radiation as “light”. Birds have a fourth color receptor for UV light, which opens up an expanded color world for them. This ability plays a significant role in orientation, food search, and mate selection (4). Researchers at Lund University have simulated the world from a bird’s perspective using multispectral cameras and found that UV vision enhances the contrast between the upper and lower sides of leaves. This allows birds to navigate better in complex, leafy habitats – a clear advantage in dense forests (5).
However, the ability to see UV radiation is not equally pronounced in all bird species. While many passerine birds such as tits, blackbirds, and zebra finches, as well as parrots, have corresponding sensory cells, birds of prey, magpies, ravens, and swifts cannot perceive UV light (6). For bird species with UV vision, this additional perceptual ability is an important tool for using plumage reflections as a sign of a partner’s attractiveness or for recognizing food and prey (7).
Sliney, D. H. (2002): “Photoprotection of the Eye – UV Radiation and Sunglasses.” Journal of Photochemistry and Photobiology B: Biology, 64(2-3), 166-175.
Land, M. F., & Nilsson, D.-E. (2012): Animal Eyes (2nd ed.). Oxford University Press, pp. 75–80.
Enoch, J. M., & Tobey, F. L. (1981): Vertebrate Photoreceptor Optics. Springer, pp. 47–48.
Cuthill, I. C., et al. (2000): “Ultraviolet Vision in Birds.” Advances in the Study of Behavior, 29, 159-214.
Tedore, C. & Nilsson, D.-E. (Lund University, Sweden): Nature Communications, doi: 10.1038/s41467-018-08142-5.
Ödeen, A. & Hastad, O. (2013): “The phylogenetic distribution of ultraviolet sensitivity in birds.” BMC Evolutionary Biology, 13:36.
Lind, O. et al. (2014): “Ultraviolet vision in birds: the importance of transparent eye media.” Proceedings of the Royal Society B, 281: 20132209.
Definitions of Spectral Categories of Solar Radiation According to ISO 21348
Ultraviolet Solar Radiation
The division of ultraviolet radiation into spectral ranges varies depending on the standard, application, and common usage.
The ISO 21348 standard provides a unified basis for describing and measuring solar radiation and is primarily used for applications in aerospace in various wavelength ranges. It is particularly important for research, climatology, space travel, and technical applications where precise information on solar radiation is required.
| Designation | Wavelength Range λ (nm) | Description |
|---|---|---|
| UV | 100 ≤ λ < 400 | Ultraviolet |
| VUV | 10 ≤ λ < 200 | Vacuum Ultraviolet |
| EUV | 10 ≤ λ < 121 | Extreme Ultraviolet |
| H Lyman-α | 121 ≤ λ < 122 | Hydrogen Lyman-alpha |
| FUV | 122 ≤ λ < 200 | Far Ultraviolet |
| UVC | 100 ≤ λ < 280 | Ultraviolet C |
| MUV | 200 ≤ λ < 300 | Middle Ultraviolet |
| UVB | 280 ≤ λ < 315 | Ultraviolet B |
| NUV | 300 ≤ λ < 400 | Near Ultraviolet |
| UVA | 315 ≤ λ < 400 | Ultraviolet A |
Space environment (natural and artificial) – Process for determining solar irradiances
In addition to the mentioned ISO 21348, CIE S 017/E:2011 is another comprehensive reference work for terms and definitions in the field of optical radiation.
CIE S 017/E:2011 and ISO 21348 are two different international standards that deal with light, radiation, and their definitions, but have different focuses and areas of application.
The standards overlap in the definition of spectral ranges but differ in objectives, structure, and application context.
| Feature | CIE S 017/E:2011 | ISO 21348:2007 |
|---|---|---|
| Objective | Standardization of terms, units, definitions in the field of light | Definition and classification of solar radiation ranges, especially for space applications |
| Content | Vocabulary, term definitions, units, symbols | Exact wavelength ranges for UV, VIS, IR, specifically for solar radiation |
| Scope of application | General lighting technology, illumination, photobiology, photochemistry | Space travel, solar technology, meteorology, solar radiation measurement |
| Example UV range | UV-A: 315–400 nm, UV-B: 280–315 nm, UV-C: 200–280 nm | UV-A: 315–400 nm, UV-B: 280–315 nm, UV-C: 100–280 nm, further subdivisions such as Far-UV, Extreme UV, etc. |
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