1.Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, that is, in the range between 400 nm and 100 nm, corresponding to photon energies from 3 eV to 124 eV. It is so-named because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet. These frequencies are invisible to most humans except those with aphakia. Near-UV is visible to a number of insects and birds.
UV light is found in sunlight and is emitted by electric arcs and specialized lights such as mercury lamps and black lights. It can cause chemical reactions, and causes many substances to glow or fluoresce. A large fraction of UV, including all that reaches the surface of the Earth, is classified as non-ionizing radiation. The higher energies of the ultraviolet spectrum from wavelengths about 120 nm to 10 nm ('extreme' ultraviolet) are ionizing, but, due to this effect, these wavelengths are absorbed by nitrogen and even more strongly by dioxygen, and thus have an extremely short path length through air.[1] However, the entire spectrum of ultraviolet radiation has some of the biological features of ionizing radiation: It does far more damage to many molecules in biological systems than is accounted for by simple heating effects (an example is sunburn). These properties derive from the ultraviolet photon's power to alter chemical bonds in molecules, even without having enough energy to ionize atoms.
Electric arcs produce UV light, and arc welders must wear eye protection to prevent welder's flash.
Although ultraviolet radiation is invisible to the human eye, most people are aware of the effect it has on the skin of fair-skinned people, i.e., the suntan and sunburn. Normal human skin responds to exposure to small doses of this kind of radiation by increasing the amount of protective melanin in the skin's outer layers; too much of this radiation in too short a period of time, however, results in cellular damage from radiation burn. In fact, the damaging effects of short-wavelength and mid-wavelength UV means that life on Earth outside of the deep oceans is possible only because the atmosphere, primarily the ozone layer, filters out the vast majority of this light.[2] A small amount of the shorter wavelength ultraviolet reaches the surface, which causes sunburn, long-term skin damage, and skin cancer. Ultraviolet is also responsible for the formation of vitamin D in organisms that make this vitamin (including humans). The UV spectrum thus has many effects, both beneficial and damaging, to human health.
The Sun's emission in the lowest UV bands, the UVA, UVB, and UVC bands, are of interest, as these are the UV bands commonly encountered from artificial sources on Earth. The shorter bands of UVC, as well as even more energetic radiation as produced by the Sun, generate the ozone in the ozone layer when single oxygen atoms produced by UV photolysis of dioxygen react with more dioxygen. The ozone layer is especially important in blocking UVB and part of UVC, since the shortest wavelengths of UVC (and those even shorter) are blocked by ordinary air. Of the ultraviolet radiation that reaches the Earth's surface, up to 95% is UVA (the very longest wavelength),[11] depending on cloud cover and atmospheric conditions.
UVA, UVB, and UVC can all damage collagen fibers and, therefore, accelerate aging of the skin. Both UVA and UVB destroy vitamin A in skin, which may cause further damage.[31] In the past, UVA was considered not harmful or less harmful, but today it is known it can contribute to skin cancer via indirect DNA damage (free radicals and reactive oxygen species). UVA can generate highly reactive chemical intermediates, such as hydroxyl and oxygen radicals, which in turn can damage DNA. The DNA damage caused indirectly to skin by UVA consists mostly of single-strand breaks in DNA, while the damage caused by UVB includes direct formation of thymine dimers or other pyrimidine dimers, and double-strand DNA breakage.[32] UVA is immunosuppressive for the entire body (accounting for a large part of the immunosuppressive effects of sunlight exposure), and UVA is mutagenic for basal cell keratinocytes in skin.[33]
Because UVA does not cause reddening of the skin (erythema), it is not measured in the usual types of SPF testing.[34] There is no good clinical measurement for blockage of UVA radiation, but it is important for sunscreen to block both UVA and UVB. Some scientists blame the absence of UVA filters in sunscreens for the higher melanoma risk found for sunscreen users.[35]
The reddening of the skin due to the action of sunlight depends both on the amount of sunlight and on the sensitivity of the skin ("erythemal action spectrum") over the UV spectrum.
UVB light can cause direct DNA damage. As noted above, UVB radiation excites DNA molecules in skin cells, causing aberrant covalent bonds to form between adjacent Pyrimidine bases, producing a dimer. Most UV-induced pyrimidine dimers in DNA are removed by the process known as nucleotide excision repair that employs about 30 different proteins.[36] Those pyrimidine dimers that escape this repair process can induce a form of programmed cell death called apoptosis or can cause DNA replication errors leading to mutation.
When DNA polymerase comes along to replicate a strand of DNA with an unrepaired pyrimidine dimer, it reads a CC dimer as AA and not the original CC. This causes the DNA replication mechanism to add a TT on the growing strand. This mutation can result in cancerous growths, and is known as a "classical C-T mutation". The mutations caused by the direct DNA damage carry a UV signature mutation that is commonly seen in skin cancers. The mutagenicity of UV radiation can be easily observed in bacterial cultures. This cancer connection is one reason for concern about ozone depletion and the ozone hole. Individuals with an inherited defect in one of the proteins necessary for nucleotide excision repair may suffer from a condition called xeroderma pigmentosum that is characterized by extreme sun-sensitivity and by a high incidence of skin cancers. (Also see DNA repair-deficiency disorder.
As a defense against UV radiation, the type and amount of the brown pigment melanin in the skin increases when exposed to moderate (depending on skin type) levels of radiation; this is commonly known as a sun tan. The purpose of melanin is to absorb UV radiation and dissipate the energy as harmless heat, blocking the UV from damaging skin tissue. UVA gives a quick tan that lasts for days by oxidizing melanin that was already present, and it triggers the release of the melanin from melanocytes. However, because this process does not increase the total amount of melanin, a UVA-produced tan is largely cosmetic and does not protect against either sunburn or UVB-produced DNA damage or cancer.[37]
By contrast, UVB yields a slower tan that requires roughly two days to develop, because the mechanism of UVB tanning is to stimulate the body to produce more melanin. However, the production of melanin by UV, called melanogenesis, requires direct DNA damage by UVB to initiate. The photochemical properties of melanin make it an excellent photoprotectant from both UVA and UVB. Older and more widespread sunscreen chemicals cannot dissipate the energy of the excited state as efficiently as melanin, and, therefore, the penetration of these sunscreen ingredients into the lower layers of the skin may increase the amount of free radicals and reactive oxygen species (ROS).[38] In recent years, improved filtering substances have come into use in commercial sunscreen lotions that do not significantly degrade or lose their capacity to protect the skin as the exposure time increases (photostable substances).[39]
Sunscreen prevents the direct DNA damage that causes sunburn, by blocking of UVB. As such, most of these products contain an SPF rating that indicates how well they block UVB as a measure of their effectiveness (SPF is, therefore, also called UVB-PF, for "UVB protection factor").[40] This rating, however, offers no data about protection against UVA, exposure to which does not lead to sunburn but is still harmful, since it causes indirect UV DNA damage and is also (along with UVB and UVC) considered carcinogenic. In the US, the Food and Drug Administration is considering adding a star rating system to show UVA protection (also known as UVA-PF). A similar system is already used in some European countries.[41] Some sunscreen lotions now include compounds such as titanium dioxide, which helps protect against UVA rays. Other UVA blocking compounds found in sunscreen include zinc oxide and avobenzone.
2.
Gunnar's website claims they protect your vision by filtering out "artificial" light, and relaxes your eyes, so you get tired slower. They also claim that it prevents dryness, but I'm not quite sure how it would go about doing that, since the glasses aren't like those James Worthy or Horace Grant goggles that encase your eyes—they're just normal glasses.
On Gunnar's own website, they claim:
GUNNARS increase contrast, comfort and focus while minimizing eye fatigue and visual stress for anyone who spends long hours staring at digital screens. GUNNAR eyewear is powered by i-AMP lens technology comprised of a proprietary lens material in an advanced geometry tuned for intermediate viewing distance and finished with custom formulated lens filters, tints and coatings.
For specific claims (that seem relevant):
Improve contrast and filter out UV.
IONIK lens tints improve overall contrast and comfort by filtering out harsh artificial light, eliminating UV rays and reducing high-intensity visible light.
Anti-reflective.
iFi lens coatings include an anti-reflective layers to reduce glare and an exterior hard coat that minimizes environmental damage and scratching.
Improved detail/focus.
FRACTYL lens geometry includes a specifically tuned focusing power to enhance detail and a highly wrapped lens design that limits air currents near the eye.
Is there any evidence that these things actually reduce eye strain or fatigue? Or that they're beneficial at all?
I've seen a couple more articles about this recently, but they seem to be providing evidence that Gunnars are better than low-quality glasses, but they market them primarily to people who don't need glasses, so I think the relevant claim is that "wearing Gunnar glasses is better than not wearing glasses".
but i would love one 
