Chlorophyll being green means it absorbs light in the red and blue area of the spectrum. Isn't this the high and low energy light? Wouldn't plants get more energy if they absorbed light in the green area of the spectrum instead of the red one?


1 Answer 1


The reason that chlorophyll is green is because it absorbs other colors of light such as red and blue, so in a way the green light is reflected out since the pigment does not absorb it.

Because life might have been purple:

It is possible that the very first life form to process light may have been purple colored. This would mean it was reflecting red and blue light and absorbing green. In such a scenario this thing if it was the first to produce energy from light would have out competed against everything else. It would have had a population explosion and possibly covered much of the Earth or at least the oceans. Haloarchaea are an example of a simple life form that uses Retinal and Bacteriorhodopsin to produce energy though far less efficiently than photosynthesis. Had this been developed prior to photosynthesis it may have let it spread very far even though it is a less efficient energy production method. A 2% efficiency increase in a market no one has yet tapped is still a huge advantage.

In this scenario because the first thing to use light was using green light it left a niche for another form of life to exploit. That niche would have been absorbtion of the Red and Blue spectrums. Which is the same area plants absorb today. They got so good at their niche that they eventually were able to generate much more energy than the first life form did and eventually out competed for the sun. This niche has worked so well that they never developed a full system for the other spectrums.

Because you could say that good enough is good enough:

The sun puts out a lot of energy. It is possible that there was no need to try and capture all of the spectrum or that it was actually not beneficial to do so. Often too much sun is more an issue than too little. Too much sun and heat can dry out the plant. It is possible that to gain the benefits of photosynthesis there needed to be a reduction in some energy to balance it out. Much like a black car on a hot summer day a black plant might absorb all of the spectrums but also get far too hot. Blue plus red may just be the sweet spot.

However, about your question about colour:

Wouldn't plants get more energy if they absorbed light in the green area of the spectrum instead of the red one?

Plants would probably get more energy if their leaves were black.


  • 5
    $\begingroup$ That first sentence basically says, "chlorophyll is green because it isn't some other color." $\endgroup$ Commented Apr 18, 2016 at 19:33
  • $\begingroup$ @amarillo feel free to edit my answer. $\endgroup$
    – Ebbinghaus
    Commented Apr 18, 2016 at 20:44
  • $\begingroup$ Absorbing higher energy may also lead to harmful photoproducts. $\endgroup$
    – Yoda
    Commented Apr 18, 2016 at 21:58
  • 3
    $\begingroup$ "Because you could say that good enough is good enough" -- this is perhaps the most important point. If there was a massive benefit to doing so, plants would likely have evolved to capture the green spectrum as well. But doing so would probably not help -- a lack of sufficient CO2 to use all the captured energy would almost certainly be the result. $\endgroup$
    – Jules
    Commented Apr 18, 2016 at 23:59
  • 1
    $\begingroup$ @Yoda Plants already absorb blue, which is more energetic than green. $\endgroup$ Commented Nov 17, 2017 at 0:59

Not the answer you're looking for? Browse other questions tagged .