It would be hard to find ideal light intensity if the temperature were cold and hot because
the photosynthesis would not happen if it is too hot then it would become too cold and denatured, then will result in cells would stop working.
Since the light-dependent reaction of photosynthesis is not affected by changes in temperature than the whole rate increases. If the temperature goes above optimum the rates begin to decrease. The enzyme is being denatured until the time it stops.
