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By 1903 it was known the most effective wavelengths were around 250 nm.In 1960, the effect of ultraviolet radiation on DNA was established.Significant examples include 193 nm photolithography equipment (for semiconductor manufacturing) and circular dichroism spectrometers.Technology for VUV instrumentation was largely driven by solar astronomy for many decades.Sensitive ultraviolet photomultipliers are available. Spectrometers and radiometers are made for measurement of UV radiation. Vacuum UV, or VUV, wavelengths (shorter than 200 nm) are strongly absorbed by molecular oxygen in the air, though the longer wavelengths of about 150–200 nm can propagate through nitrogen.Scientific instruments can therefore utilize this spectral range by operating in an oxygen-free atmosphere (commonly pure nitrogen), without the need for costly vacuum chambers.While optics can be used to remove unwanted visible light that contaminates the VUV, in general, detectors can be limited by their response to non-VUV radiation, and the development of "solar-blind" devices has been an important area of research.Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared to silicon diodes.
UV radiation is present in sunlight, and contributes about 10% of the total electromagnetic radiation output from the Sun.Ultraviolet has a higher frequency (and thus a shorter wavelength) than violet light.UV radiation was discovered in 1801 when the German physicist Johann Wilhelm Ritter observed that invisible rays just beyond the violet end of the visible spectrum darkened silver chloride-soaked paper more quickly than violet light itself.The long end of the EUV spectrum is set by a prominent He spectral line at 30.4 nm.EUV is strongly absorbed by most known materials, but it is possible to synthesize multilayer optics that reflect up to about 50 percent of EUV radiation at normal incidence.
UVA makes up almost all UV light that penetrates the Earth's atmosphere.