Light conversion efficiencies

Fig. 3. Maximum theoretical photosynthetic light conversion efficiency of water to H2 using sunlight. The arrows indicate efficiency losses at various stages after photosynthesis starts, and the remaining efficiency at each stage is indicated as a percentage.

In summary, an optimal H2-photoproducing biological system would have to be able to function at high rates and with about 10% solar light conversion efficiency in an aerobic atmosphere, simultaneously evolving H2 and O2 gases at a ratio of 2 1. Materials and gas separation issues, as well as photobioreactor designs to address these, will be discussed in section 5.3. 

The emission spectrum of Nal(Tl) peaks at 410 nm, and the light-conversion efficiency is the highest of all the inorganic scintillators (Table 6.1). As a material, Nal(Tl) has many undesirable properties. It is brittle and sensitive to temperature gradients and thermal shocks. It is also so hygroscopic that it should be kept encapsulated at all times. Nal always contains a small amount of potassium, which creates a certain background because of the radioactive... 

CsI(Tl). CsI(Tl) has a higher density (4.51 X 10 kg/m ) and higher atomic number than Nal therefore its efficiency for gamma detection is higher. The light-conversion efficiency of CsI(Tl) is about 45 percent of that for NaKTl) at room temperature. At liquid nitrogen temperatures (77K), pure Csl has a light output equal to that of Nal(Tl) at room temperature and a decay constant equal to 10 s. The emission spectrum of CsI(Tl) extends from 420 to about 600 nm. 

Anthracene has a density of 1.25 X 10 kg/m and the highest light conversion efficiency of all organic scintillators (see Table 6.3)—which is still only about one-third of the light conversion efficiency of Nal(Tl). Its decay time ( 30 ns) is much shorter than that of inorganic crystals. Anthracene can be obtained in different shapes and sizes. 

To measure the energy of the incident particle with a scintillator, the relationship between the pulse height and the energy deposited in the scintillator must be known. Because the pulse height is proportional to the output of the photomultiplier, which output is in turn proportional to the light produced by the scintillator, it is necessary to know the light-conversion efficiency of the scintillator as a function of type and energy of incident radiation. The rest of this section presents experimental results for several cases of interest. 

Typha and other similar aquatic marsh plants have nutrient concentrations as % of dry matter of about 0.5-3% N, 0.1 -0.3% P, and 1.6-3.5% K (1 ). The actual nutrient concentration depends on the part of plant analyzed, the season (or age of plant), and, most importantly, on the nutrient supply to the plant. Nutrient limitation reduces light conversion efficiency and productivity. However, the minimal concentrations required to maintain healthy growth are not well characterized. Critical nutrient tissue levels (at which nutrient deficiency sets in) are 0.09% for P and 2.5% for K in a Typha hybrid (52) for nitrogen it is likely between 0.5-1.0%. For supply of such nutrient levels on a large-scale a number of sources can be considered — agricultural fertilizers, sewage and animal wastes, and recycled nutrients from a processing plant. 

The objectives of this study were 1) to examine the possibility that photoinhibitory reduction of photosynthetic CO2 assimilation occurs in over-wintering annual crops and 2) to examine whether photoinhibitory depression of photosynthesis at low temperatures in Z. mays and B. napus crops corresponds to significant depression of light conversion efficiency, and hence production, at the whole crop level. 

This process directly uses water as hydrogen source, but it presents a very low efficiency, mainly because of oxygen inhibition of hydrogenase and low light conversion efficiency (light saturation effect Hallenbeck Benemann, 2002). 

Specialty gas discharge short arc sources based on mixed metal and rare earth salts for solar simulation, usually referred to as metal halide - global, (MHG) lamps, are also used in solar simulation. One advantage is the high electrical power to light conversion efficiency making them well suited for very large scale illumination, especially when employed in arrays. These lamps also... 

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