The McCree Curve represents the average photosynthetic response of plants to light energy (see chart below). It was developed by Dr. Keith McCree in the 1970s based on his research of 22 plant species. He found that much of a plant’s development and response to light happened within this portion of the spectrum. 

The McCree Curve, also known as the Plant Sensitivity Curve, begins at 350nm and extends to 750nm. Later studies extended this curve out to 300nm to 800nm. This curve can be placed over a spectral distribution chart as a guide to how well a light source can affect photosynthesis.