Sunlight, 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 ). ...

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. 

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).

Figure 1. Energy distribution, as a function of wavelength, of a high pressure xenon arc lamp and noon summer sunlight (4)...

Pig. 10. Energy distribution of various artificial ultraviolet sources, (a) Sunlight, (b) xenon arc, (c) carbon arc, (d) mercury lamp, (e) fluorescent lamp [reproduced with permission from Ref. 15],... 

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). 

The interaction between EM radiation and matter includes experiences of everyday life. If a piece of iron is heated in the blacksmith s shop, it will turn red after a while. With further heating, the color changes to yellow. Everything heated to 6000°C will be as white as sunlight. The frequency distribution and color of the heated body depend only on its temperature. Wien had arrived at his displacement law and even derived an equation for the energy distribution, but it did not fit perfectly to very accurate measurements of energy distribution as a function of frequency. 

When we are trying to reduce heat we normally care about sunlight Figure 24.1 shows two curves that describe the intensity of light coming from the sun as a function of wavelength. The top curve is the energy distribution of an ideal black-body with temperature of 5800 K, and is based on Eq. (24.1). 

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 6.2. Energy distribution of the sunlight spectrum. A. Monochromatic mercury lamp at 254 nm. B. Black light lamp. (From Crosby, 1972.) American Chemical Society. Reprinted with permission.

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... 

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