There are three main factors affecting photosynthesis and several corollary factors.

These are:

- Light irradiance and wavelength
- Carbon dioxide concentration
- Temperature

At constant temperature, the rate of carbon assimilation varies with irradiance, initially increasing as the irradiance increases. However at higher irradiance this relationship no longer holds and the rate of carbon assimilation reaches a plateau.

At constant irradiance, the rate of carbon assimilation increases as the temperature is increased over a limited range. This effect is only seen at high irradiance levels. At low irradiance, increasing the temperature has little influence on the rate of carbon assimilation.

As carbon dioxide concentrations rise, the rate at which sugars are made by the light-independent reactions increases until limited by other factors.