Ultraviolet:
Since the wavelength of an EM disturbance become shorter than the smallest we can view, the energy enclosed in each individual photon rises. The UV range of wavelengths begins at about 390 nm and expands down to around 1 nm. At a wavelength of around 290 nm, the atmosphere becomes extremely absorptive, and at wavelengths shorter than this, air is necessarily opaque. This protects the atmosphere against damaging ultraviolet radiation from the Sun. The Ozone (molecules having three oxygen atoms) in the upper environment is principally responsible for this effect. The Ozone pollution, common in large cities throughout the summer months, additional attenuates UV.
Normal glass is virtually opaque at UV; therefore cameras with glass lenses cannot be used to take photographs in this portion of the spectrum. Rather, a pinhole-type device is used, and this strictly limits the quantity of energy which passes into the detector. Whereas a camera lens has a diameter of numerous millimeters and centimeters, the pinhole is less than a millimeter across. The other type of device which can be used to logic UV and to measure its intensity at different wavelengths is the spectrophotometer. The diffraction grating is used to scatter EM energy into its constituent wavelengths from IR via the visible and into the UV range. By moving the sensing device back and forward, any preferred wavelength can be singled out for analysis. The main principle of operation of the spectrophotometer is shown in figure below. At the tremendously short-wavelength end of the UV spectrum (i.e., hard UV), radiation counters are at times used, similar to the apparatus employ for the detection of x-rays & gamma rays. For photographic purposes, normal camera film will work at the longer UV wavelengths (i.e., soft UV). The special film, instead such as x-ray film, is essential to make hard-UV photos.
Figure: Functional diagram of a spectrophotometer that can be used to sense and measure EM radiation at IR, visible, and UV wavelengths.
The UV rays hold an interesting property which can be observed using a so-called black light. Most of the hobby shops sell lamps of this kind. They are cylindrical in shape, and apparently, they can be incorrect for small fluorescent tubes. (The luminous black light bulbs sold in department stores are not particularly good sources of UV.) Whenever subjected to UV, certain substances glow brightly in the visible range. This is termed as fluorescence. The Art stores sell acrylic paints which are specially tailored to glow in different colors whenever UV strikes them. The effect in a darkened room can be prominent. The phosphor coatings on CRTs fluoresce beneath UV also. Therefore will certain living organisms, like scorpions. When you live in the desert, go outside a few nights with a black light and switch it on. When there are scorpions around, you will find out.
Most of the radiation from the Sun takes place in the IR and visible portions of the EM spectrum. When the Sun were a much hotter star, generating more energy in the UV range, life on any earth-like planet in its organization would have developed in a dissimilar way, if at all. The excessive exposure to UV, even in the relatively small quantities which reach the Earth's surface on bright days, can, over time, cause eye cataracts and skin cancer. There is proof to recommend that excessive exposure to UV restrain the activity of the immune system, rendering people and animals more vulnerable to infectious diseases. A few scientists believe that the ozone hole in the upper environment, prevalent in the southern hemisphere, is growing since of raised production and emission of certain chemicals by human kind. When this is the situation, and when the problem worsens, we must expect that it will affect the development of life on this planet.