Researchers tested the effect of light on the rate of photosynthesis by a species of shrub growing under conditions that differ widely in the amount of available light but where the availability of water and soil nutrients is fairly constant. Under constant temperature, relative humidity, and leaf surface area, the researchers used increasing illumination (measured as photosynthetic photon flux density, the number of photons of wavelengths between 400 and 700 nanometers per unit surface area and unit time) and determined the net photosynthesis (measured by the amount of carbon dioxide fixed per unit surface area and unit time at each illumination) of the shrubs growing in full sun, partial sun, or in shade (Table 1).