What colors of light are most effective for photosynthesis?

• A. Green and yellow light.
• B. Red and blue light only.
• C. Orange and yellow light.
• D. Red, blue, and violet light are most effective for photosynthesis.

Answer: (D)

Photosynthesis relies on pigments in chloroplasts absorbing light energy to power the light reactions. The pigments absorb blue and red wavelengths most efficiently, so light in those parts of the spectrum provides the most energy for driving the reactions. Violet light also falls in a range that pigments can absorb, so it contributes to photosynthesis, though not as prominently as blue and red. In contrast, green and yellow light are mostly reflected by plants and are not absorbed well, so they are less effective at driving photosynthesis. Therefore, red, blue, and some violet light are the most effective colors for photosynthesis, with green and yellow being relatively ineffective.