At low temperatures 0 to 10 degrees Celsius the enzymes that control many reactions in the chloroplasts do not work very well and there is a decline in photosynthesis. The ideal temperature that these enzymes work is between 10-20 degrees Celsius. Again at higher temperatures the enzymes are damaged and the photosynthesis has a decline also.
The chlorophyll of the plants absorb in the red and violet wavelength which are not seen by the plants that is why they are green. The violet light has the shortest wavelength and the most energy whereas the red has the highest wavelength in the visible spectrum and the least energy.
Light intensity affect photosynthesis
Light intensity or light quantity refers to the total amount of light that plants receive.
The intensity of light can change with the time of the day, season, geographic location, distance from the equator, and weather. It gradually increases from sunrise to the middle of the day and then gradually decreases toward sunset; it is high during summer, moderate in spring and fall, and low during winter time.
At low light intensities, as light intensity increases, the rate of the light-dependent reaction, and therefore photosynthesis generally, increases proportionately (straight line relationship).
As light intensity is increased further, however, the rate of photosynthesis is eventually limited by some other factor. So the rate plateaus. At very high light intensity, chlorophyll may be damaged and the rate drops steeply (not shown in the graph).
The point is to find which date the photosynthesis performs better both in terms of temperature and light intensity and that should be when the temperature is between 10 to 20 degrees Celsius and towards a day in the year that the light intensity is moderate. In areas with latitude 38 degrees North that time of the year can be either in October November or February March when both the conditions are fulfilled. (Moderate light and temperature).