In the process of photosynthesis, which colour of visible light is least effective for most green plants?

Introduction / Context:

This science question tests basic knowledge of photosynthesis and the light absorption properties of plant pigments. Chlorophyll, the main pigment in green plants, absorbs certain wavelengths more efficiently than others. Competitive exams often ask which colour of light is least effective in driving photosynthesis, because it connects the observable green appearance of leaves with underlying absorption and reflection patterns.

Given Data / Assumptions:

Concept / Approach:

Chlorophyll pigments absorb light most strongly in the blue and red regions of the spectrum and reflect most of the green region. That is why leaves look green to our eyes. Because green wavelengths are largely reflected or transmitted rather than absorbed, they contribute the least to photosynthetic energy capture. Therefore, green light is the least effective colour for photosynthesis, whereas blue and red light are comparatively more effective.

Step-by-Step Solution:

Verification / Alternative check:

A quick verification is to think about experiments where plants are grown under different coloured lights. Plants under red and blue light generally grow better than those under purely green light. In addition, absorption spectra of chlorophyll show high absorption peaks in blue and red regions and low absorption in the green region. Both lines of reasoning agree that green light is relatively ineffective for photosynthesis in typical green plants.

Why Other Options Are Wrong:

Blue light: Chlorophyll absorbs blue wavelengths strongly, and blue light is actually very effective in driving photosynthesis and regulating plant growth.

Red light: Red light is another major absorption region for chlorophyll and is highly effective in photosynthetic energy capture.

Sunlight: Sunlight is a mixture of all visible wavelengths and is the natural source of light for plants; it is certainly not the least effective overall.

Common Pitfalls:

Some candidates misinterpret the question and think that because leaves appear green, green light must be the most useful, whereas it is actually the most reflected and least absorbed. Others confuse the term least effective with least abundant. To avoid this, always connect the green colour of leaves with reflection, not absorption. Once that link is clear, it becomes intuitive that green light contributes the least to photosynthesis.

Final Answer:

The correct answer is Green light.