Threshold light intensity

Fig. 12. The transition rate, t 1 of the 5WS10CH cylindrical gel as a function of the light intensity at several temperatures. The arrow indicates the threshold light intensity estimated from Fig. 5(b)...

Under conditions of a constant Al the rate of uptake of alanine increases linearly with the light intensity. A threshold light intensity is required before alanine uptake occurs. These results strongly indicate a direct interaction between the alanine carrier and the electron transfer chain. 

Fig. 10-2. Threshold contrast in distinguishing an object from its surroundings. The eye responds to an increment in light intensity by increasing the number of signals (pulses) sent to the brain. The detection of threshold contrast involves the ability to discriminate between the target (1) and the brighter background (/ + A/). Source Gregory, R. L., Eye and Brain "The Psychology of Seeing." Weidenfeld and Nicolson, London, 1977.

Equation (1) predicts that at low light intensities mutants of type (i) or (ii) have a raised threshold, since either reduction of a or Ptot can be compensated by raising I (Fig. 16). At high light intensities unbleached photoreceptor becomes limiting and one has to take into consideration the ratio Pbi/Ptot this ratio depends on the intensity I and the cross section a ... 

Figure 7.11 shows the evolution of Raman spectra by increasing the light intensity of illumination. It is important to point out the existence of a certain threshold intensity of the incident laser beam—below 7th, the initial shape of the spectrum was recovered after turning off the illumination above it, the spectrum further transforms... 

On the basis that the position of Etn at the semiconductor surface is dependent on the photon flux and that Etn has to lie above the HER redox level, a threshold in light intensity has been proposed217 for the sustained photoelectrolysis of water to occur. However, as discussed by other authors,218 no such threshold has been reported in the literature. It has been pointed out218 that the driving force for the photoinduced electron transfer process is related to the difference in standard potentials of the donor (say, an electron at the semiconductor CB edge) and the acceptor (say, protons in solution). This is independent of the carrier concentration and photon flux and thus a light intensity threshold for incipient product formation through photoelectrolysis should not occur.218... 

The experimental observations217 of an apparent light intensity threshold for the photocurrent onset have been rationalized218 on the basis that a critical photon flux must be exceeded to counteract the dark current of opposite polarity flowing through the cell. Thus, there appears to be confusion between alternate definitions of a light intensity threshold a threshold for incipient product (say H2) formation and a threshold for product formation in a specific (e.g., standard) state,218... 

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