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Painting

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Painting taken literally is the practice of applying pigment suspended in a carrier (or medium) and a binding agent (a glue) to a surface (support) such as paper, canvas or a wall. However, when used in an artistic sense it means the use of this activity in combination with drawing, composition, or other aesthetic considerations in order to manifest the expressive and conceptual intention of the practitioner. Painting is also used to express spiritual motifs and ideas; sites of this kind of painting range from artwork depicting mythological figures on pottery to The Sistine Chapel to the human body itself. Origins and early history edit Like drawing, painting has its documented origins in caves and on rock faces. The finest examples, believed by some to be 32,000 years old, are in the Chauvet and Lascaux caves in southern France. In shades of red, brown, yellow and black, the paintings on the walls and ceilings are of bison, cattle, horses and deer. Paintings of human figures can be fo...
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Applications

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Because of its ability to cause chemical reactions and excite fluorescence in materials, ultraviolet radiation has a number of applications. The following table gives some uses of specific wavelength bands in the UV spectrum 13.5 nm : Extreme ultraviolet lithography 30–200 nm : Photoionization, ultraviolet photoelectron spectroscopy, standard integrated circuit manufacture by photolithography 230–365 nm : UV-ID, label tracking, barcodes 230–400 nm : Optical sensors, various instrumentation 240–280 nm : Disinfection, decontamination of surfaces and water (DNA absorption has a peak at 260 nm), germicidal lamps 200–400 nm : Forensic analysis, drug detection 270–360 nm : Protein analysis, DNA sequencing, drug discovery 280–400 nm : Medical imaging of cells 300–320 nm : Light therapy in medicine 300–365 nm : Curing of polymers and printer inks 350–370 nm : Bug zappers (flies are most attracted to light at 365 nm) Photography edit Photographic film responds to ultraviolet radiation...
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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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