A limiting factor is a factor which controls (and therefore limits) the rate of photosynthesis.
If you had a plant, and you increased the intensity of light, the rate of photosynthesis would increase.
However, there comes a point where the light is so intense that the rate of photosynthesis becomes constant. This means that the maximum rate of photosynthesis has been reached.
In order to increase the rate further, the plant needs to be warmer, and have a higher concentration of Carbon Dioxide (so that the amount of reactants it is taking in can be enough for the plant to use the…