Light solar constant

The total intensity of sunlight outside the earth s atmosphere is characterized by the solar constant, defined as the total amount of light received per unit area normal to the direction of propagation of the light the mean value is 1368 W m-2, although variations from this mean are common (Lean, 1991). 

Switzerland, yielded the spectrum reproduced in Fig. 5.40. The numerical values upon which this diagram is based can be found in M. Iqbal [5.34]. The maximum of EfAn lies in the visible light region at A pa 0.45 /tm. 99 % of the irradiance falls in the wavelength band A < 3.8 fim. Fig. 5.40 also shows the spectral irradiance EXa of the radiation emitted by a black sun at Ts = 5777 K. The areas under the two curves (up to A —> oo) are equal — they each yield the solar constant E0 —, but the spectrum of the extraterrestrial solar radiation deviates significantly at some points, in particular at A < 0.6//.in, from the spectrum of radiation from a black body. 

Simple models for louvers and other solar protection devices are based on a statement of constant reduction of the solar radiation flux on the window. A common assumption is that a louver is controlled so that no direct light can penetrate into the room. 

The rate of photolytic transformations in aquatic systems also depends on the intensity and spectral distribution of light in the medium (24). Light intensity decreases exponentially with depth. This fact, known as the Beer-Lambert law, can be stated mathematically as d(Eo)/dZ = -K(Eo), where Eo = photon scalar irradiance (photons/cm2/sec), Z = depth (m), and K = diffuse attenuation coefficient for irradiance (/m). The product of light intensity, chemical absorptivity, and reaction quantum yield, when integrated across the solar spectrum, yields a pseudo-first-order photochemical transformation rate constant. 

Small differences in light sources have definite effects on photochemical processes. Some irradiation systems match the solar spectrum poorly, thus affecting the relative importance of the various photodissociation processes occurring in the atmosphere. Ambient variations in the nitrogen dioxide photolysis pseudo-first-order rate constant,... 

Beryllium-10 P-decays to 10B with a half-life of 1.5 Myr. Beryllium and boron (along with lithium) are several orders of magnitude less abundant than the other light elements in the solar system because, except for 7Li, they are not produced in stars. They are produced when high-energy cosmic rays, mostly protons, fragment atomic nuclei into small pieces in a process called spallation. Beryllium-10 is constantly being produced at low levels by spallation in the solar system, and its abundance in bulk meteorites is used to estimate the amount of time that they were exposed to cosmic rays as small bodies (their cosmic-ray... 

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