hz this component is progressively damped with increasing frequency because of the time required for oxygen diffusion from the chloroplasts to the gas phase thus at high frequency only the photochemical loss persists and the transient decrease in this case fig4 c reflects the gradual onset of photochemistry lowering the measured heat release upon light absorption during photosynthetic induction modulated co 2 uptake does not contribute significantly to the signal being strongly damped due to successive intermediary reactions involving relatively slow rate constants and large pool sizes which separate between the photoact and co 2 uptake fig5 shows steady state measurements the interpretation of which is again that at low frequencies fig5 c 15 hz the change introduced by background light is due to oxygen evolution and that at high frequencies fig5 a 425 hz it is due to photochemical energy storage both effects measuring photosynthetic activities an intermediate effect is obtained at intermediate frequencies fig5 b 150 hz the numbers in the figure give the background light intensity in w m 2 used fig6 shows the use of measurements such as those shown in fig4 to follow the distribution of incident illumination between the two photosystems in green plant leaves if modulated light is used that is effective mainly in exciting photosystem i ii an enhancement of photochemical activity i e oxygen evolution is seen when continuous background light is used that is effective mainly in exciting photosystem ii i while no such effect is seen when 34 white 34 continuous background light is used such measurements are useful for example for studying the effects of environmental conditions on.