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23

You're talking about long-wave UV, or UV-A radiation. In the 80s, experts claimed that this was a safe wavelength. Protection against UV-A was not part of sunscreen in the early days. Consequently, UV-A was (and still is) used in tanning beds due to its perceived safety over UV-B. However, a lot of research has been done since. UV-A is well understood now ...


17

Rather than 'breaks' caused by high energy radiation, UV radiation causes chemical modifications of the bases ('letters') that make up DNA. There are four bases in the DNA alphabet abbreviated to A,T,G or C belonging to two classes. A & G are guanines while T & C are pyrimidines. When you have pyrimidine bases next to each other on a DNA strand, they ...


15

There are very many photochemical reactions: Up to 50–100 mutagenic reactions on DNA per second might occur in a skin cell during exposure to sunlight, but are usually corrected within seconds by photolyase reactivation or nucleotide excision repair. (That's just DNA, excluding O2 and other cell constituents) chemist ref and wiki ref Molecules that absorb ...


6

There are (at least) two sides to this story. One is direct DNA damage being caused by UV-B light which happens to have photons with just the right amount of energy to interact with thymine. This has been known, and assumed not just during the 80s, but until the late 2000s to be The One major thing that causes cancer, or trouble in general (there's papers ...


6

The CDC's disinfection guidelines lists UV radiation between 328 and 210nm as effective for disinfection, with a maximum of bactericidal activity occurring between 240-280nm. At this wavelength DNA damage (Thymine dimers) is induced with a high rate. Due to practical reasons UV light is mostly used to disinfect water, if used in rooms there is some ...


4

Our skin contains quite a lot of water and I think this is answers the question: The absorption of UV light by this water goes drastically up when you shift to shorter wavelengts with a minimum absorption in the UV-A spectrum. See this figure (from here): So water has a very low absorption around 340-350nm (UV-A) and a very high absorption at shorter ...


3

The damage to your eye does not only come from UV exposure, but also from infrared (IR) radiation. Your eye contains a lens that focuses the incoming rays to a narrow point. This point would get very hot if you looked directly into the sun. This is comparable to focussing the sun on a piece of paper with a magnifying glass, it would start to burn. Also, the ...


3

Behar-Cohen et al. notes the periphery of the cornea has a focusing effect: UVR incident from the periphery is refracted into the eye, and due to the focusing effect of the cornea, UV radiation is on average 22-fold stronger at the nasal limbus, which is the typical site for pterygium and pinguecula. Moreover, UV radiation is on average eight times ...


2

Yes. Natural sunlight doesn't have a good substituent. Melatonin levels and circardian rhythms are directly affected by natural sunlight. As far as LEDs goes, a french study concluded that blue light may have photochemical risks and affect our retina. Source http://www.ledinside.com/knowledge/2014/4/...


2

Physics/Chemistry aside, as @mimat and @aliential awesomely explained, it's always good to keep in mind that cancer, in general, is a statistics game, in the sense that at any time, there's a cell suffering mutation in your body, and it is not manifesting as cancer simply because your body evolved to deal with those situations. You can take a walk on the ...


1

Your question contains the word "efficient". The most efficient method is the one with achieves the goal with the minimum of effort or disadvantages. And that totally depends on what you want to do exactly. If you have a surface like a lab bench, you use ethanol or iso-propanol because its cheap, quick, relatively safe to use for that purpose and dries up ...


1

The life of the radicals decides how far they move. This paper https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4310837/#!po=6.92308 has a table of half lives of radicals, the longest lasting ones (the radical of nitrous oxide and nitrogen dioxide) have half lives of seconds. Diffusion theough the skin would be slow Technically the problem is "reactive oxygen ...


1

You can make homemade bacterial growth medium. https://www.madaboutscience.com.au/shop/science-extra/post/grow-bacteria-on-homemade-agar-plates/ Basically it is just nutrient jello: beef stock, sugar, gelatin to make a firm surface. It would be nice to have all your cultures in uniform plates or cups. You could order petri dishes or use what you have ...


1

You should have a look at wikipedia > melanin. Melanin is a broad term for a group of natural pigments found in most organisms. [..] Melanin is an effective absorber of light; the pigment is able to dissipate over 99.9% of absorbed UV radiation.1 Because of this property, melanin is thought to protect skin cells from UVB radiation damage, reducing the ...


1

The wavelength of UV-C most effective at provoking mutagenesis in DNA is 260 nm, which has been shown to kill Cryptosporidium parvum at doses below 10 mJ/sq cm. http://www.ncbi.nlm.nih.gov/pubmed/12834745 In units of lux, 10^5 lux of sunlight has been shown to kill 99.9% of Aeromonas salmonicida after two hours of exposure. http://www.sciencedirect.com/...


1

UV Rays kill the cells by damaging the DNA. UV lights do not disrupt the cell membrane. If a cell is exposed to UV light, it creates THYMINE dimers (bond). Thymine dimers are the actual disruption in the kinks of DNA. UV exposure to skin is proportional to the cell damage. P53 is a gene product which takes care of fixing cell damage. However it has a ...


1

Some physical methods of sterilisation are in hospitals Steam autoclaving Dry heat – thermostat White light / UV light sterilization where continuous UV light has poor penetration. UV radiation heat is absorbed by proteins and nucleic acid. All micro-organisms contain tehm. They inactivate the DNA. There will be electronic and photochemical reactions ...


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