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I have learned throughout my basic science classes in high school that in the process of photosynthesis, plants absorb sunlight & produce food. They use carbon dioxide & water vapour.

My doubt is if I draw an analogy with solar cells, they convert electricity from sunlight. When the sunlight directly falls on the solar cell, it produces more electricity but even when it is cloudy & no direct sunlight is available, they do produce electricity but with less efficiency.

So do plants require ONLY direct sunlight or does photosynthesis also occur during cloudy weather when no sunlight is available but the surroundings are bright.

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Yes, photosynthesis does occur on cloudy days where the light exposure is diffuse - but the overall picture is not as simple as your solar cell analogy.

Consider one of the findings of the following article: "Impact of clear and cloudy sky conditions on the vertical distribution of photosynthetic CO2 uptake within a spruce canopy" (Urban et al. 2011), where one of the findings is that

that shoots from deep within the canopy contribute substantially to the overall carbon balance during cloudy days. But, although shade-adapted shoots had a markedly positive carbon balance over a 24-h period on cloudy days, their performance was impaired on sunny days contributing only a marginal or even negative carbon balance from the middle and shaded parts of the canopy.

So, while leaves at the top of the canopy have a reduced rate of photosynthesis on cloudy days, leaves within the canopy and those that are shade-adapted, still photosynthesised.

I hope this helps a bit.

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Moreover, chlorophylls don't absorb all wavelengths equally. See here –  WYSIWYG Jul 4 '13 at 14:42
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