Spectrum, reference solar

The deterioration of the stratospheric ozone layer over Antarctica permits excessive amounts of solar nltraviolet radiation (UV) to reach the surface of the continent (Appendix 2.11.5). The increase in the intensity of UV radiation in Antarctica affects organisms on land and in the oceans as described in a book edited by Weiler and Penhale (1994). A summary by Graedel and Crutzen (1993) of the health effects of UV radiation indicates that it causes skin cancer in light-skinned individuals. Studies referred to by them indicate that a 1% reduction in the inventory of stratospheric ozone increases the effective UV dose by 2%, which causes a 4% increase in the incidence of the basal-cell carcinomas and about a 6% increase in the incidence of squamous-cell carcinomas. Therefore, unless special precautions are taken, geologists and other people who usually work out-of-doors in Antarctica during September and October may be exposed to higher doses of UV radiation than persons elsewhere on the Earth. The energy spectrum of solar UV radiation is discussed in Appendix 2.11.3. 

One of the problems which must be solved for quantitative measurements by emission is the need for a blackbody source at the temperature of measurement. And a variety of blackbody references have been used including a V-shaped cavity of graphite 164), a metal plate covered with a flat black paint1S6 160) and a cone of black paper l53). However, none of these methods of producing a blackbody reference spectrum are adequate. In most cases the efficiency of the reference has not been established. The most recent recommendation 1S0) is an aluminium cup painted with an Epley-Parsons solar black lacquer which has an emittance of greater than 98% over the infrared spectral range. 

Iodide of potassium was employed for a similar purpose but these do not give results as satisfactory as the hyposulphite of soda introduced by Sir J. Her-schell. Other improvements by the latter philosopher have also to be recorded, whloh, though not bo important as the one just referred to, contributu, nevertheless, to the perfection of the art. This Is particularly the case with hie researches on the solar spectrum, the results of which have been already given, and by which he has laid the foundation of the principles of actinism, and brought it to its present comprehensive state,... 

Fig. 10.11. The solar spectrum. AMO indicates that the graph refers to conditions outside the normal atmosphere. (Taken on earth, the spectrum is more complicated because it is indented at wavelengths corresponding to absorption by constituents of the atmosphere.) Note that the relation between the wavelength in micrometers and the energy in electron results is 1.3 eV = pm. Thus, 0.2 urn = 6eV and 2.0 pm =...

The match between a simulator spectrum E s(A) and the reference AM 1.5G spectrum r(A) is never perfect, even for the best solar simulators. Furthermore, a spectral mismatch is introduced because the spectral responses St (A) of the device under test and Sr.(A) of the reference cell are not identical. In order to correct for this, a spectral mismatch factor M can be computed from... 

Each element has its own line spectrum. This is why the line spectrum for an element is also considered to be a fingerprint for that particular element. Because the amounts of light given off by the excited atoms were in fixed amounts, Bohr termed them quantized amounts of light. These fixed amounts of energy proved that the electrons could only make certain jumps between the orbits that were at fixed distances in the atom. Because of these fixed, circular orbits, Bohr s model of the atom is often referred to as the solar system model of the atom (see Figure 3.4). 

Radiometric quantities are important to describe and measure UV and VUV radiation. They are usually subdivided into energetic, spectral and photonic terms. Energetic terms (Tab. 3-9) are based on the energy of the radiation and they refer to all relevant wavelengths. Eor each of these terms a spectral derivative can be defined (Bolton, 1999) which is correlated with a specific wavelength X. Eor example, the extraterrestrial solar spectrum incident on the upper atmosphere is represented by the mean spectral irradiance Eq in W m nm over a defined wavelength interval AX in nm (CIE, 1989). Further, each of the spectral units can easily be transferred to photon-based units, which themselves are related to radio-metric units (cf Braun et al., 1991). 

Reference to the previously cited CIE (7), ISO (9), and ASTM (18) standards will reveal that the xenon-arc lamps with appropriate filters are widely used to simulate this spectrum. This is because the properly filtered xenon-arc lamp is the best representation of solar light of any lamp produced. 

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