Here's what he did:
* Experiment: He used a prism to split sunlight into its different wavelengths (colors). Then, he illuminated a filament of the green alga *Cladophora* with these different wavelengths.
* Observation: He noticed that the bacteria (which use oxygen) congregated around the parts of the alga illuminated by red and blue light. This indicated that those wavelengths were most effective in promoting photosynthesis, leading to the production of oxygen.
* Conclusion: This experiment established that chlorophyll, the pigment responsible for photosynthesis, absorbs most strongly in the red and blue regions of the light spectrum, leading to higher rates of photosynthesis.
This discovery was crucial for our understanding of photosynthesis, laying the foundation for further research on the mechanism and importance of this process.