 The spectral levels of light that can be used by plants for photosynthesis is similar to, but not the same as what's measured by lumens.Therefore, when it comes to measuring the amount of light available to plants for photosynthesis, biologists often measure the amount of photosynthetically active radiation (PAR) received by a plant.PAR designates the spectral range of solar radiation from 400 to 700 nanometers, which generally corresponds to the spectral range that photosynthetic organisms are able to use in the process of photosynthesis.