Intensity distribution, sunlight

Louis curve for June 1966 is broader than that for Los Angeles in August. This is explained by differences in sunlight intensity distribution throughout the day. 

Figure 1. UV absorptions and sunlight intensity distribution. For lOfi films.

We have modified a 1 kW Oriel xenon light source to provide an 8 inch illuminated circle with light between 300 and 1,000 nm to simulate sunlight for our prototype device. We have measured the light intensity distribution in the circle so that we can correct for effects of non-uniformity in the light field on the performance of photocatalysts. 

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 effect of light scattering and absorption by atmospheric constituents on the intensity and wavelength distribution of sunlight at the earth s surface depends on both the nature and concentration of the gases and particles as well as the path length through... 

For example, some may have short lifetimes and/or nonuniform distributions and hence be sensitive to such factors as the location of the emissions, sunlight intensity, season, etc.)... 

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 experimentally determined value of j is, of course, only measured under one particular set of atmospheric conditions. Since the photolysis rate depends on the intensity and spectral distribution of the sunlight it is useful to quote the photolysis rate coefficient relative to a conventional measure of solar light intensity, such as 7(N02). The value for 7 (aldehyde)//(N02) can be used to calculate the photolysis rate of the aldehyde under a range of atmospheric conditions. 

The UV energy in sunlight varies in wavelength distribution and intensity with the time of day and year as well as latitude and elevation of exposure. The presence of water also depends on the region, time of year, etc. Therefore, predicting natural weather resistance from laboratory tests can be difficult. 

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