question: There’s been a few demonstrations on how sunblock covered skin looks darker under a uv-camera; but shouldn’t it be better for the skin to look brighter, meaning it reflects more of the uv rays away and into the camera?
comment: Either/Or is fine. A material doesn't need to reflect light in order to block it. Think of a black vs. white cloth for example. Both may work as a good shade blocking light from the other side. But the black cloth is absorbing most wavelengths of visible light where as the white cloth is reflecting them.
passages: A type of plenoptic camera using a low-cost printed film mask instead of a microlens array was proposed by researchers at MERL in 2007. This design overcomes several limitations of microlens arrays in terms of chromatic aberrations and loss of boundary pixels, and allows higher-spatial-resolution photos to be captured. However the mask-based design reduces the amount of light that reaches the image sensor compared to cameras based on microlens arrays.
  
  Section::::Technology.:Stereo with plenoptic cameras.
   There is some indication that washing fabrics in detergents containing fabric brighteners, which absorb UV radiation, might increase their protective capability. Studies at the University of Alberta also indicate that darker-colored fabrics offer more protection than lighter-colored fabrics.
  
  While there is some correlation between the percentages of visible light and UV that pass through the same fabric, it is not a strong relationship. With new-technology textiles designed for the sole purpose of UV blocking, it is not always possible to judge the UV protection level simply by holding up the fabric and examining how much visible light passes through.
   Historically, photographic films were mostly sensitive to UV light, which caused haziness or fogginess, and in color films a bluish hue. Therefore, as a standard, a UV (blocking) filter was used, transparent to visible light while filtering out shorter ultraviolet wavelengths. However, newer photographic film and digital cameras are highly insensitive to UV wavelengths. UV filters are sometimes referred to as L37 or L39 filters, depending on the wavelengths of light that they filter out; an L37 filter removes ultraviolet light with a wavelength shorter than 370 nanometers (nm), whereas an L39 filter eliminates light with a wavelength shorter than 390 nm.
   Digital cameras sensors may have internal filters that block UV to improve color rendition accuracy. Sometimes these internal filters can be removed, or they may be absent, and an external visible-light filter prepares the camera for near-UV photography. A few cameras are designed for use in the UV.
  
  Photography by reflected ultraviolet radiation is useful for medical, scientific, and forensic investigations, in applications as widespread as detecting bruising of skin, alterations of documents, or restoration work on paintings. Photography of the fluorescence produced by ultraviolet illumination uses visible wavelengths of light.
   Unlike most digital cameras, there is no IR or UV filtering in front of the image sensor. This results in a wide spectral response of approximately 1000 nm to 380 nm (infrared to ultraviolet). Suitable external bandpass filters are required to photograph in IR or UV wavelengths. Infrared filters are readily available at low cost from many sources, but ultraviolet filters – and suitable lenses – can be expensive.
   To increase efficiency, a shallow and uncovered plate must be used. Also, rotation of the samples located under the UV right may be necessary to make sure they receive even UV irradiation, and thus to, yet again, improve the cross-linking efficiency. If the cross-linking is done in vivo, within living cells, these must be exposed to the UV radiation during a period of 15 minutes or less.
  
  Section::::Uses.
   In reflected UV photography the subject is illuminated directly by UV emitting lamps (radiation sources) or by strong sunlight. A UV transmitting filter is placed on the lens, which allows ultraviolet light to pass and which absorbs or blocks all visible and infrared light. UV filters are made from special colored glass and may be coated or sandwiched with other filter glass to aid in blocking unwanted wavelengths. Examples of UV transmission filters are the Baader-U filter or the StraightEdgeU ultraviolet bandpass filter, both of which exclude most visible and infrared light. Older filters include the Kodak Wratten 18A, B+W 403, Hoya U-340 and Kenko U-360 most of which need to be used in conjunction with an additional infrared blocking filter. Typically such IR blocking, UV transmissive filters are made from Schott BG-38, BG-39 and BG-40 glass. Filters for use with digital camera sensors must not have any "infrared leak" (transmission in the infrared spectrum); the sensor will pick up reflected infrared radiation as well as ultraviolet, which may obscure the details that would be resolved by ultraviolet alone.
   Suitable digital cameras for reflected UV photography have been reported to be the (unmodified) Nikon D70 or D40 DSLRs, but many others are suitable after having their internal UV and IR blocking filter removed. The Fujifilm FinePix IS Pro digital SLR camera is purpose-designed for ultraviolet (and infrared) photography, with a frequency response rated from 1000-380 nm, although it also responds to somewhat longer and shorter wavelengths. Silicon (from which DSLR sensors are made) can respond to wavelengths between 1100-190 nm.
  
  Section::::Equipment and techniques.:UV induced fluorescence photography.
   Normally, the glass or plastic of a camera lens is practically opaque to short-wavelength UV, but transparent to long-wavelength (near-visible) UV. A UV filter passes all or nearly all of the visible spectrum but blocks virtually all ultraviolet radiation. (Most spectral manipulation filters are named for the radiation they pass; green and infrared filters "pass" their named colors, but a UV filter "blocks" UV.) It can be left on the lens for nearly all shots: UV filters are often used mainly for lens protection in the same way as clear filters. A strong UV filter, such as a Haze-2A or UV17, cuts off some visible light in the violet part of the spectrum, and has a pale yellow color; these strong filters are more effective at cutting haze, and can reduce purple fringing in digital cameras. Strong UV filters are also sometimes used for warming color photos taken in shade with daylight-type film.
   Many photographers and cinematographers still use UV filters as a protection for their lenses' glass and coating. However, UV filters, as with any filter may introduce lens flare and have an adverse impact on contrast and sharpness. Hoods offer some protection against impact and shade optical elements, preventing lens flare, but quality UV filters offer some protection against lens contamination while minimising the inherent additional distortion. 
   Within the ultraviolet light range (λ = 180 to 400 nm), the primary absorber in the body is DNA and RNA. By using ultraviolet photoacoustic microscopy, DNA and RNA can be imaged in the cell nuclei without the use of fluorescence labeling. Since cancer is associated with DNA replication failure, UV photoacoustic microscopy has the potential to be used for early cancer detection.
  
  Section::::Contrast.:Endogenous Contrast Agents.:Visible Light Absorbers.
   Clear filters, also known as window glass filters or optical flats, are transparent and (ideally) perform no filtering of incoming light. The only use of a clear filter is to protect the front of a lens.
  
  UV filters are used to block invisible ultraviolet light, to which most photographic sensors and film are at least slightly sensitive. The UV is typically recorded as if it were blue light, so this non-human UV sensitivity can result in an unwanted exaggeration of the bluish tint of atmospheric haze or, even more unnaturally, of subjects in open shade lit by the ultraviolet-rich sky.
   About 1 percent of the population suffer from vitiligo. Photo therapy is an effective treatment because the skin cells manufacture the pigment when they sense UV light. When they sense UV light the cells manufacture the pigment in order to protect the body from the harming UV light. Treatment is generally required 3 times a week in a clinic and every day at home. It takes about 1 month to achieve re-pigmentation in the face and neck, and 2–4 months in the hands and legs. Narrowband UVB is more suitable to the face and neck and PUVA is more effective at the hands and legs.
   They are often used for "one-day" only tans, or to complement a DHA-based sunless tan. Many formulations are available, and some have limited sweat or light water resistance. If applied under clothing, or where fabric and skin edges meet, most will create some light but visible rub-off. Dark clothing prevents the rub-off from being noticeable. While these products are much safer than tanning beds, the color produced can sometimes look orangey and splotchy if applied incorrectly.
   Narrowband UVB therapy is less effective for the legs and hands, compared to the face and neck. To the hands and legs PUVA may be more effective. The reason can be because UVA penetrates deeper in the skin, and the melanocytes in the skin of the hands and legs are positioned deeper in the skin. Narrowband UVB 311 nanometer is blocked by the topmost skin layer, and UVA 365 nanometer reaches the melanocytes that are in the bottom skin layer.
   Microscopy with UV surface excitation
  
  Microscopy with UV Surface Excitation (MUSE) is a novel microscopy method that utilize the shallow penetration of UV photons (230 - 300 nm) excitation. Compared to conventional microscopes, which usually require sectioning to exclude blurred signals from outside of the focal plane, MUSE’s low penetration depth limits the excitation volume to a thin layer, and removes the tissue sectioning requirement. The entire signal collected is the desired light, and all photons collected contribute to the image formation.
  
  Section::::Mechanism.
   Photography based on visible fluorescence induced by UV radiation uses the same ultraviolet illumination as in reflected UV photography. However, the glass barrier filter used on the lens must now absorb or block all ultraviolet and infrared light and must permit only the "visible" radiation to pass. Visible fluorescence is produced in a suitable subject when the shorter, higher energy ultraviolet wavelengths are absorbed, lose some energy and are emitted as longer, lower energy visible wavelengths.
   UV filters are individual compounds or mixtures that block or absorb ultraviolet (UV) light. Two major applications of UV filters are in sunscreens, where they protect the skin from sunburn and other damage, and in photography, where they are used to coat a glass disc which fits on top of the lens. These have become less necessary with digital cameras, as the medium is less sensitive to ultraviolet light. When exposed to UV light, these filters can undergo transformations into other chemicals that are less protective and possibly toxic. As a result, there are practical concerns about the choice of chemical to use beyond just which has the desired filtering properties.
   Ultraviolet irradiation can be used to excite nucleic acids and create photoreactions, which results in damaged bases in the DNA strand. Photoreactions can include: single strand breaks, interactions between or within DNA strands, reactions with solvents, or crosslinks with proteins. The workflow for this method has an additional step, once both your protected and unprotected DNA have been treated, there is subsequent primer extension of the cleaved products. The extension will terminate upon reaching a damaged base, and thus when the PCR products are run side-by-side on a gel; the protected sample will show an additional band where the DNA was crosslinked with a bound protein. Advantages of using UV are that it reacts very quickly and can therefore capture interactions that are only momentary. Additionally it can be applied to "in vivo" experiments, because UV can penetrate cell membranes. A disadvantage is that the gel can be difficult to interpret, as the bound protein does not protect the DNA, it merely alters the photoreactions in the vicinity.
   UV induced visible fluorescence photography must take place in a darkened room, preferably with a black background. The photographer should also wear dark-colored clothes for better results. (Many light-colored fabrics also fluoresce under UV.) Any camera or lens may be used because only visible wavelengths are being recorded.
  
  UV can also induce infrared fluorescence and UV fluorescence depending on the subject. For UV induced "non-visible" fluorescence photography, a camera must be modified in order to capture UV or IR images, and UV or IR capable lenses must be used.
   As with infrared filters there is a potential ambiguity between UV-blocking and UV-passing filters; the latter are much less common, and more usually known explicitly as UV pass filters and UV bandpass filters.
  
  Section::::Neutral density.
   UVA is blocked less than UVB by many sunscreens, but is blocked to some degree by clothing. UVA is known both to cause DNA damage and to be carcinogenic. However, it operates not by inducing direct DNA damage, but by producing reactive oxygen species which damage DNA indirectly. UVA (see above) induces a cosmetic tan but little extra melanin protection against sun damage, sun burn, or cancer. 
  
  Section::::Tanning process.:UVB.
  
  Ultraviolet B (UVB) radiation is in the wavelength range 280 to 320 nm. Much of this band is blocked by the Earth's ozone layer, but some penetrates. UVB:
   Suspended nanoparticles in stained glass prevent UV rays from causing chemical reactions that change image colors. A set of stained glass color reference chips is planned to be used to calibrate the color cameras for the 2019 ESA Mars rover mission, since they will remain unfaded by the high level of UV present at the surface of Mars.
   While determining how much UV light should be filtered by art glazing, it may also be important to consider the amount of UV light present inside a room or a building. Note that regular window glazing filters away a significant portion of the UV light, which originates from the sun.
  
  The relative amounts of damaging light in equal quantities of light:
   Section::::Measurements of protection.:UVA protection.:Persistent pigment darkening.
  
  The persistent pigment darkening (PPD) method is a method of measuring UVA protection, similar to the SPF method of measuring sunburn protection. Originally developed in Japan, it is the preferred method used by manufacturers such as L'Oréal.
  
presuppositions: Sunblock works by reflecting uv rays. Sunblock covered skin should appear lighter on camera, since it means it reflects more uv rays away.
corrections: Sunblock can work by reflecting uv rays or by absorbing them. Sunblock does not need to reflect light in order to block it.
raw_presuppositions: Sunblock works by reflecting uv rays. Sunblock covered skin should appear lighter on camera, since it means it reflects more uv rays away.
raw_corrections: Sunblock can work by reflecting uv rays or by absorbing them. Sunblock does not need to reflect light in order to block it.