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The Effect of Light Intensity on Photosynthesis

Image by, courtesy of epSos .de

Photosynthesis is much more important to humans than we would imagine. It affects everything in the biological chain, either directly or indirectly. How the process is affected with slight changes is also integral in our understanding of how we can better harness the process for desired environmental results.

Photosynthesis Basics

The process of photosynthesis converts energy from sunlight into chemical forms that can be used by plants, bacteria and protisians. This chemical form is normally sugar, which cellular respiration (transfer of energy from various molecules) produces ATP (adenosine triphosphate), a form of energy that is used by living things.


Cyanobacteria, also known as blue-green algae, are responsible for a large portion of the photosynthesis that takes place in the ocean. They have different pigments, called phycobilins, which are red or blue and absorb light that other plants do not.

Light Wavelength

Light wavelength (the distance between light waves) factors into how plant pigments absorb and process light energy. Wavelengths less than 400 nm (nanometers) and above 700 nm are generally not usable by plants and cyanobacteria. Most pigments don't absorb ultraviolet light well, and if the wavelength is too low they can become damaging to plant cells.

Contrary to what many may think, yellow light is not effectively absorbed by chlorophylls and carotenoids, the pigments in plants and the reason why plants are green. Blue, red, and blue-green light are absorbed while the others are reflected and pass through.

Light Intensity

The light intensity range for most plants falls between 1,200 and 2,000 lumens (measurement of light intensity). The number of light photons hitting the chlorophyll pigments increase as the light intensity rises. This in turn increases the rate of photosynthesis.

The whole process is so effective that in optimum conditions 90 percent of light is absorbed.

The Benefits Of Photosynthesis

The number one benefit derived from photosynthesis is the oxygen humans need to breathe. It does this by a process using water and carbon dioxide, with some plants being more efficient than others.

For example, one hectare (2.471 acres) of corn produces enough oxygen per day in midsummer to meet the respiratory needs of 325 people. One million hectares could produce enough oxygen for a population of 10 million in about eleven summer days, which could last them the whole year.

Another benefit is the removal of CO2 from the atmosphere. Much of this is oxidized by living organisms for survival.

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