Sunlight, spectral energy distribution

Figure 2. Spectral energy distribution of sunlight at the earth s surface for solar angles of 10°, 40°, and 90°, from direct sun (--) or reflection from open sky (--) (5 ). ...

Figure 6-3 Spectral Energy Distribution of Sunlight (S), CIE IUuminant (A), Cool White Fluorescent Lamp (B), and Sodium Light (N)...

Hirt RC, Schmitt RG, Searle ND, Sullivan AP. Ultraviolet spectral energy distribution of natural sunlight and accelerated test light sources. J Opt Soc Am 1960 50(7) 706-713. 

Figure 5.2 Sunlight spectral energy distribution in UV (ISO 4892, part 3 — informative annex).

These are useful in so far as they reproduce to a fair approximation the spectral energy distribution of sunlight and provide a control of temperature and humidity. From among the several instruments that are commercially available, some of the most extensively used are briefly described here. 

Diurnal and seasonal variations in solar intensity are, of course, of utmost importance to ecosystems. In the extreme polar regions there is no direct solar radiation at all for more than four months of the year, whereas near the equator the overall intensity of sunlight fluctuates less than 10% annually. The spectral energy distribution also varies with the season. For example, in July in the middle latitudes (ca. 40 ), the fraction of shorter-wave UV (290-315 nm) in the total solar radiation is more than three times higher than it is in December, due to the shorter path these easily scattered wavelengths have to traverse through the atmosphere. For similar reasons, shortwave UV is more intense at high elevations, particularly in the tropics where stratospheric ozone is less concentrated (Caldwell et al., 1980). 

Xenon arc lamps create a stable energy distribution very well adapted to sunlight over the entire spectrum, including the infrared range. A number of filters are available to users to specify the adaptation of spectral energy distribution, s. Figure 2.15 [215]. 

The spectral energy distribution of sunlight does not depend on the orientation of a detector, whereas the spectral energy distribution of skylight and daylight depends on the plane in which the measurements are made. 

The relative spectral energy distribution of sunlight outside the earth s atmosphere is shown in Figure 10.119. 

The relative spectral energy distributions of sunlight, skylight and daylight as a function of solar altitude are shown in Figures 10.120,10.121 and 10.122, respectively. 

Fig. 10.122. Relative spectral energy distribution of daylight (sunlight plus skylight) on a 15-0° plane for a clear atmosphere for solar altitudes of70,40,20 and 10° [2293].

Fig. 10.136. Spectral energy distribution of (—) 6500 W xenon arc lamp employed in Atlas Weatherometers and (—) noon summer sunlight at Chicago, Illinois, USA.

Fig. 2,6 Spectral energy distribution curves of a Sunlight, b Incandescent light, and c Fluorescent light. 1998, M.V. Orna...

Fig. 2.8 Spectral energy distribution curve of ordinary sunlight (a), absorption spectrum of a red opaque object (b), transmittance spectrum of a transparent red object (c). 1980, American Chemical Society, Ref. [15]...

Figure 5-3. Spectral energy distribution of sunlight and fluorescent lamp. (Courtesy of Q-Panel Lab Products.)...

A water-cooled xenon-arc-type light source is one of the most popular indoor exposure tests since it exhibits a spectral energy distribution of sunlight at the... 

The question is, in the presence of a UV absorber, how much li ht is left to be absorbed by the photosensitizer in a pol5mier The calculations of the protective efficiency of UV absorbers for a polymeric system can be made by means of the spectral energy distribution of sunlight and the absorption spectra of the absorbers and the pol3mier. 

Hirt, R. H. Ultraviolet spectral energy distributions of natural sunlight and accelerated light sources. National Meeting of the Optical Society of America, Detroit, Mich. (Oct. 9, 1 ). 

The efficiency in this section is defined at 25°C under 1000 W/m2 of sunlight intensity with the standard global air mass 1.5 spectral distribution. Thus, 15 percent module efficiency refers to peak watt efficiency (Wp) and implies that 15 percent of the incident sunlight energy is converted to electricity. 

The spectral distribution in sunlight is important for structural-physical applications. The surface of the sun has a temperature of about 5000 K. Thus the maximum of the radiated energy lies in the visible area of 200-300 nm. Sunlight is weakened on its way to the earth s surface through various mechanisms which absorb the energy. For this reason the Planck spectral distribution can be seen as an envelope curve for the radiation arriving on the earth s surface (Fig. 5.20). The real circumstances are also shown in the figure. 

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