What Is An Action Spectrum

What Is An Action Spectrum

If you are wondering what an action spectrum is, we’ve got you covered here. Getting to know about the action spectrum in various plants will give you an idea of how plants make use of different lights for their development.

The lights we see consist of various wavelengths and light has a comprehensive relationship with plants. Plants will either absorb or reflect the different colors of the light spectrum. This absorption or reflection affects the process of photosynthesis that will determine how your plants process their food.

Now, let’s have a discussion about the role of the light absorption spectrum, light action spectrum, and how they are connected to photosynthesis. We will also talk about various plant pigments, their functions and, many more. So, let’s begin.

Absorption And Action Spectrum

Both absorption spectrum and action spectrum play a significant role in the plant process of photosynthesis. Let’s go further by looking at what these two entails and discuss more details on them.

What Is An Action Spectrum?

Firstly, let’s define what the action spectrum is. An action spectrum is an illustration (usually showed in a graph) that reveals the rate of photosynthesis at various light wavelengths. Thus, it illustrates the wavelength that propels photosynthesis.

Action spectrum was first discovered and titled by T.W. Engelmann when he was researching on algae Cladophora. The action spectrum gives an insight into the nature of the photoreceptor involved. It also helps us understand the differences between the absorption spectrum of a known pigment. Action spectrum will illustrate the usefulness or effectiveness of light in photosynthesis.

Maximum photosynthesis usually takes place in the red and blue light spectrum. Next, let’s take a look at what the action spectrum of photosynthesis is.

Photosynthesis Action Spectrum

The action spectrum of photosynthesis in any given plant will indicate high light absorption for red or violet and orange or red color spectrum. It will also show maximum light absorption in the blue region. However, it will indicate a low absorption rate for the green or yellow color spectrum.

The colors blue and violet on the light spectrum have the shortest wavelength and the highest energy. On the other hand, red has the longest wavelength and has the least amount of energy.

Absorption Spectrum

The absorption spectrum will indicate all the colors of light absorbed by a given plant. It describes the electromagnetic radiation range of plant absorption. It relies on the cellular and molecular structure of a plant. So, it varies depending on the plant species.

Absorption And Action Spectrum


The pigment is a common name used for a molecule that takes in or absorbs light with color. Also, we can term pigment as any chemical compound that assimilates visible radiation between 380 nm (which is violet) and 760 nm (which is red).

These pigments assimilate light rays from the visible part of the electromagnetic spectrum known as photosynthetically active radiation (PAR).

Now, any type of colored substance generated by a plant is known as plant pigment. There are different pigments contained in plants and they result in the different colors we see. These plant pigments give rise to leaves’ color, flowers, as well as fruits. Now the most crucial function this pigment offers is control over the photosynthesis process with plants’ growth and development.

Plant pigments will only absorb the wavelength of light ranging from 700 nm to 400 nm. Now, this is the ideal PAR range for plants.

Below are the 3 major plant pigments that determine plant color:


This pigment is one of the most important in plants because it is directly involved in the plants’ photosynthesis. Their absorbing wavelength spectrum is 429 nm and 659 nm. They are also responsible for the violet-blue and orange-red colors.

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They are accessory pigments. Involved indirectly in photosynthesis. Even though plants can’t photosynthesize with carotenoids, this pigment can still transfer the light energy they get down to chlorophyll.

Carotenoid pigments are photo-receptive agents that prevent harmful reactions. They are also responsible for the orange, bright yellow, and red colors in various plants, vegetables, and fruits.


This pigment plays a crucial role in the reproduction of plants. It as well helps by attracting pollinators and seed disperses. They are, however, not directly involved in the photosynthesis process. But just like carotenoids, they also help shield plants from harmful rays.

Absorption Spectrum Of Chlorophyll

Chlorophyll is a type of pigment and in nature, we have 6 types of chlorophyll. However, in plants, there are 2 major types of chlorophyll which are chlorophyll A and chlorophyll B. The region of the spectrum that plant chlorophyll absorbs differs for both chlorophylls A and B.

Chlorophyll A and B have different roles they play in photosynthesis. Chlorophyll A is the main pigment that is involved in photosynthesis. On the other hand, chlorophyll B is a supplementary pigment that receives light energy which it will pass to chlorophyll a.

Absorption Spectrum Of Chlorophyll

The color spectrum that chlorophyll A absorbs is violet and orange. On the other hand, the color spectrum that chlorophyll B absorbs is blue and yellow. Both chlorophyll a and b hardly absorb the green spectrum. The green light is reflected rather than being absorbed. So, this results in the green color of most plants.

Additional Say On What Is An Action Spectrum

We hope by now you have been enlightened on what an action spectrum is and you can see the role they play in a plant’s photosynthetic process and developments.

Remember, the absorption spectrum of chlorophyll that determines photosynthesis lies in the blue and red regions. Also, light wavelengths within the range of 400 nm to 700 nm are utilized by plants for photosynthesis and this is the ideal PAR range.