Light concentrator

These units are claimed to provide conversion efficiencies of up to 25%, or even 30% if the irradiation level is high enough. High irradiation is defined as 200-300 suns (1 sun = 0.1 W/cm2), which correspond to 20-30 W/cm2 of solar irradiation. To obtain such levels of solar irradiation, the solar light has to be focused 200-300 times. For a light concentration ratio of 100x, the high-performance PV cells are claimed to have a conversion efficiency of 28%. 

Sensitivity and selectivity would be enhanced when one is operating in the fluorescence mode if the light source selected for excitation were to emit light concentrated solely in a narrow band at wavelengths that correspond with the wavelengths of maximum absorption (maximum excitation) for the particular pesticide. 

Figure 7.15 Two slit experiment demonstrating the interference of monochromatic light. Concentric curves (cylinders) represent locations of maximum intensity of light waves propagating from the slit sources. Dimensions have been accentuated for clarity generally the slits are 0.1 mm wide and 1 mm apart, the distance from the source slit to the double slit screen is 0.6 m and from the double slit to the screen, 3 m [16). As the double slits are brought closer together, more interference fringes will appear on the screen.

Einstein A coefficient Einstein B coefficient Velocity of light Concentration Distance... 

In the case of application of photobioreactor based on porous matrix together with light concentrators, the sheets with purple bacteria should be fixed as shown in Fig. 2. The distance between sheets as well as the depth of the sheets should be determined experimentally. In both cases an illuminated surface is much lower than an occupied surface. 

Heating-Stage Microscopic Observations. Following the characterization of the mineral suites by x-ray diffraction techniques, each LTA concentrate was heated in a heating stage mounted on a microscope fitted for observation in vertically incident light. Concentrates examined in this way and the product phases are found in Table II. 

D. also alter the light concentration as another variable. 

Being illuminated the semiconductor is by no means at equilibrium. Nonetheless, under certains conditions both the electron ensemble and the hole ensemble, each one taken separately, may be assumed to be at equilibrium. Therefore, certain "electrochemical potential" is to be assigned to each ensemble separately these are called "quasi-Fermi levels", Fp and F. They, naturally, do not coincide with F, the difference depends on how far the non-equilibrium (light) concentration of corresponding current carriers declines from the equilibrium (dark) value. E g, for holes the difference equals to. 

Inverse response does not affect the operation of schemes 16.46, d (except when boilup fluctuates), because boilup is maintained constant. Inverse response of the column may have some effect on scheme 16.4a. In principle, it can temporarily raise the lights concentration in the bottom product, and momentarily lower the control tray temperature, following a heat input increase. However, the author is not aware of any troublesome experiences, even though scheme 16.4a is widely used. It appears that controller tuning is sufficient to prevent any significant ill effects of inverse response on scheme 16.4a, and that inverse response is seldom, if at all, troublesome with this scheme. 

To compute gains for dyes in LSC s, Batchelder (12) made several calculations Invoking Equation 14 and the CODE (see previous sections) of the dye. It was found -that an LSC can achieve higher light concentrations when the Stokes shift was increased. Selfabsorption ceases to limit the flux gain for a dye like DCM, whose Stokes shift corresponds to about 0.7 eV. Of course, in real calculations (12) one must include the spectral distribution of absorption and emission and not the average wavenumbers. 

Focus of the light could be done by optical system lens, Fresnel lens, mirror, etc. Converging lenses allow light concentration at the focal point. A Fresnel lens is a series of concentric rings having the shape of a prism section. It is a planoconvex lens, which allows weight saving compared to traditional lenses. Fig. 21.7 compares profiles of both a Fresnel and a conventional convex lens, with equivalent lens-focus distance. The Fresnel lens seems to have been carved from the mass of the conventional lens. 

Thus, it is particularly advantageous to ensure that the focal point of a Fresnel lens matches with the top of the optical fibre acceptance cone then, it becomes possible to have a maximum light concentration without loss. This configuration is shown in Fig. 21.8 (Nakamura, 1992). 

Parabolic mirrors are also very effective for concentrating the light at a focal point. Fig. 21.9 (Nakamura, 1992) and Fig. 21.10 (Nakamura, 2009) show two examples of configurations used for light concentration. Each configuration is arranged so that the focal point of the mirror matches with the top of the acceptance cone. 

Figure 21.8 Light concentration and propagation using Fresnel lens and optical fibres, according to (Nakamura, 1992).

Another solution for obtaining a greater light concentration is to enlarge the acceptance cone of the optical fibre. Thus, we increase the number of rays able to propagate without loss in the fibre. Different geometrical solutions to increase the numerical aperture of the fibre exist, shown in Fig. 21.11 (Nakamura, 1992). 

Draper built a light concentrator based on a convex lens that had been prepared in such a way that the focal point remained the same during all of the sun progress in the sky. The sample was placed in that point and irradiated. Considerable heath was evolved, as shown by the melting of various substances, including silver chloride. In chlorine water, water was consumed much faster than it was by exposure to non-concentrated light, and iron oxide oxalate evolved carbon dioxide and led to a precipitate of the Fe(ll) oxalate, likewise at a much enhanced rate. 

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