The color of light that maximizes the rate of photosynthesis generally falls within the red and blue wavelengths of the spectrum. Specifically, chlorophyll, the primary pigment involved in photosynthesis, absorbs light most efficiently in the blue (around 430-450 nm) and red (around 640-680 nm) ranges.
While both blue and red light are crucial, research often indicates that red light can be particularly effective in promoting photosynthesis, especially during certain stages of plant development. However, plants usually utilize a combination of various wavelengths for optimal growth and photosynthesis, including some green light, which is often reflected rather than absorbed.
In summary, while both red and blue light significantly enhance photosynthesis, red light is often considered to be the most effective.