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Does the light color spectrum and frequency matter for photosynthesis?

Does the light color spectrum and frequency matter for photosynthesis?


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Do plants grow differently when given sun light, wolfram lamp, fluorescent light, LED light, infrared, ultraviolet, x-ray, unfocused laser and stroboscope?


It matters a lot. Take a look at this graph:

This graph is for the "normal" plants containing chlorophyll.

There're also "abnormal" :-) ones, simple water plants and cyanobacteria, that contain various phycobilins for photosynthesis instead of the chlorophyll.

If your question is practical, I'd recommend using specialy-designed fluorescent lamps called grow light.


Color of light matters. As the Answer with the graph shows, chlorophyll absorbs certain colors of light best. It is strange that it does not seem to absorb yellow light well, considering that the sun has the highest emission level there, but perhaps it was to keep the plants from roasting in excessive sun conditions.

I did an experiment in High School where I placed colored transparent gel material over otherwise identical plants. One was the control with no box over it, then there was Red, Yellow, Green and Blue. The Yellow and Green did very poorly and the plants appeared to be whitish, perhaps due to inadequate chlorophyll production? The plant under the Blue appeared normal, and the one under Red grew 'leggy' and very fast. This is a known result that plants growing under foliage tend to receive excess red relative to blue light, and it triggers rapid growth, presumably so that the part of the plant can get out from under other foliage.

In my apartment and workplace, I have north-facing windows, sometimes the shades are closed during the day, both factors simulating red-light effect, and the Wandering Jew plants that I have grow like crazy.


Best light spectrum for my plants

Many first time grow light users or those who want to start to dabble into growing their plants under artificial lighting at first are very confused about all the different color temperatures or color spectrums of T5 grow light bulbs, so here is a little guide to help you understand them and to use your lights better and to their full potential.

First off I should explain a bit more about the terms that will be used in this article and that need to be known for you to fully understand grow lights. I previously mentioned a color temperature, and what that means is that the color temperature is the measurement that shows in what hue your grow light will be, and it is measured in Degrees Kelvin or Kelvins for short. Color spectrum or the visible spectrum is the light that we can see with our eyes, we can differ various colors or hues of the light, but when it comes to be precise then better to stick with the color temperature measurement to ensure that your plants get the light they need in the specific stage of their growth.


Blue Light

Blue light is of course a main contributor to photosynthesis via chlorophyll, but it also influences a plant in other ways. Blue light is typically encountered in nature at midday, when the angle of the sun is directly vertical or close to it. This would usually be a time of peak intensity and heat, therefore in many plants high intensities of blue light cause the chlorophylls to migrate to the bottom of the cell for shielding. Moreover, cryptochrome is a phytochemical that absorbs the blue spectrum and initiates phototropism (growing towards light), plus sets a plants circadian rhythm (in combination with phytochrome and the photoperiod). Interestingly, strong blue light reduces leaf intermodal length in a plant and causes it to grow compact and bushy, not wasting energy on stem length, which would be unnecessary in blue dominant full sun conditions. Many growers use blue light to keep plants compact and under control. In addition plant stomata number increases with the intensity of the blue light fraction, possibly increasing photosynthetic rates further.

Carotenes (an antioxidant orange pigment in carrots and many orange fruits and vegetables responsible for vitamin A) are stimulated by blue light, producing an orange - red spectrum through excitation and emittance.

Similarly, many flavonoids are produced in the plant using blue photons (and others). Flavonoids help a plant filter out UV light, produce colour to attract insect pollinators, for nitrogen fixation, immune system and cellular function. Anthocyanin and flavonoids are heavily dependent on blue light, produced through phototropins in biosynthesis.

Lycopenes are another product generated with blue light and have great health benefits for humans. Tomatoes grown under lights with a strong blue presence will have much higher lycopene levels than under those without.

  • Makes plants bushier and compact, reducing internode length
  • Can slow down photosynthesis slightly overall by hiding chloroplast at high intensity
  • Produces healthier and nutrient richer plants
  • Helps set the circadian rhythm

The longer wavelengths of light are red in color. The most important wavelengths in the red spectrum are from 640 to 680 nm. These wavelengths encourage stem growth, flowering and fruit production, and chlorophyll production. The red wavelengths are known as warm light, and they are naturally more prevalent in sunlight during the shorter days of fall and winter.

Some of the green and yellow light that reaches the plant is reflected, giving the plant a green color. While most of the absorbed wavelengths are in the red and blue ranges, plants do use some green and yellow light in the photosynthesis process. A light source that provides light in the entire visible range will better meet the needs of the plant.


Absorption of Light

Pigments, like chlorophyll and carotenoids, absorb and reflect light at a certain region of the electromagnetic spectrum.

Learning Objectives

Differentiate between chlorophyll and carotenoids.

Key Takeaways

Key Points

  • Plant pigment molecules absorb only light in the wavelength range of 700 nm to 400 nm this range is referred to as photosynthetically-active radiation.
  • Violet and blue have the shortest wavelengths and the most energy, whereas red has the longest wavelengths and carries the least amount of energy.
  • Pigments reflect or transmit the wavelengths they cannot absorb, making them appear in the corresponding color.
  • Chorophylls and carotenoids are the major pigments in plants while there are dozens of carotenoids, there are only five important chorophylls: a, b, c, d, and bacteriochlorophyll.
  • Chlorophyll a absorbs light in the blue-violet region, chlorophyll b absorbs red-blue light, and both a and b reflect green light (which is why chlorophyll appears green).
  • Carotenoids absorb light in the blue-green and violet region and reflect the longer yellow, red, and orange wavelengths these pigments also dispose excess energy out of the cell.

Key Terms

  • chlorophyll: Any of a group of green pigments that are found in the chloroplasts of plants and in other photosynthetic organisms such as cyanobacteria.
  • carotenoid: Any of a class of yellow to red plant pigments including the carotenes and xanthophylls.
  • spectrophotometer: An instrument used to measure the intensity of electromagnetic radiation at different wavelengths.

Absorption of Light

Light energy initiates the process of photosynthesis when pigments absorb the light. Organic pigments have a narrow range of energy levels that they can absorb. Energy levels lower than those represented by red light are insufficient to raise an orbital electron to an excited, or quantum, state. Energy levels higher than those in blue light will physically tear the molecules apart, a process called bleaching. For example, retinal pigments can only “see” (absorb) 700 nm to 400 nm light this is visible light. For the same reasons, plant pigment molecules absorb only light in the wavelength range of 700 nm to 400 nm plant physiologists refer to this range for plants as photosynthetically-active radiation.

The visible light seen by humans as the color white light actually exists in a rainbow of colors in the electromagnetic spectrum, with violet and blue having shorter wavelengths and, thus, higher energy. At the other end of the spectrum, toward red, the wavelengths are longer and have lower energy.

Visible Light: The colors of visible light do not carry the same amount of energy. Violet has the shortest wavelength and, therefore, carries the most energy, whereas red has the longest wavelength and carries the least amount of energy.

Understanding Pigments

Different kinds of pigments exist, each of which has evolved to absorb only certain wavelengths or colors of visible light. Pigments reflect or transmit the wavelengths they cannot absorb, making them appear in the corresponding color.

Chlorophylls and carotenoids are the two major classes of photosynthetic pigments found in plants and algae each class has multiple types of pigment molecules. There are five major chlorophylls: a, b, c and d, along with a related molecule found in prokaryotes called bacteriochlorophyll.

With dozens of different forms, carotenoids are a much larger group of pigments. The carotenoids found in fruit, such as the red of tomato (lycopene), the yellow of corn seeds (zeaxanthin), or the orange of an orange peel (β-carotene), are used to attract seed-dispersing organisms. In photosynthesis, carotenoids function as photosynthetic pigments that are very efficient molecules for the disposal of excess energy. When a leaf is exposed to full sun, the light-dependent reactions are required to process an enormous amount of energy if that energy is not handled properly, it can do significant damage. Therefore, many carotenoids are stored in the thylakoid membrane to absorb excess energy and safely release that energy as heat.

Each type of pigment can be identified by the specific pattern of wavelengths it absorbs from visible light, which is the absorption spectrum. Chlorophyll a absorbs light in the blue-violet region, while chlorophyll b absorbs red-blue light. Neither a or b absorb green light because green is reflected or transmitted, chlorophyll appears green. Carotenoids absorb light in the blue-green and violet region and reflect the longer yellow, red, and orange wavelengths.

Chlorophyll a and b: (a) Chlorophyll a, (b) chlorophyll b, and (c) β-carotene are hydrophobic organic pigments found in the thylakoid membrane. Chlorophyll a and b, which are identical except for the part indicated in the red box, are responsible for the green color of leaves. β-carotene is responsible for the orange color in carrots. Each pigment has (d) a unique absorbance spectrum.

Many photosynthetic organisms have a mixture of pigments. In this way organisms can absorb energy from a wider range of wavelengths. Not all photosynthetic organisms have full access to sunlight. Some organisms grow underwater where light intensity and quality decrease and change with depth. Other organisms grow in competition for light. Plants on the rainforest floor must be able to absorb any light that comes through because the taller trees absorb most of the sunlight and scatter the remaining solar radiation

Pigments in Plants: Plants that commonly grow in the shade have adapted to low levels of light by changing the relative concentrations of their chlorophyll pigments.

When studying a photosynthetic organism, scientists can determine the types of pigments present by using a spectrophotometer. These instruments can differentiate which wavelengths of light a substance can absorb. Spectrophotometers measure transmitted light and compute its absorption. By extracting pigments from leaves and placing these samples into a spectrophotometer, scientists can identify which wavelengths of light an organism can absorb.


The effects of water on light absorption

Red wavelengths are absorbed in the first few metres of water. Blue wavelengths are more readily absorbed if the water contains average or abundant amounts of organic material. Thus, green wavelengths are often the most common light in deep water.

Chlorophylls absorb red and blue wavelengths much more strongly than they absorb green wavelengths, which is why chlorophyll-bearing plants appear green. The carotenoids and phycobiliproteins, on the other hand, strongly absorb green wavelengths. Algae with large amounts of carotenoid appear yellow to brown, those with large amounts of phycocyanin appear blue, and those with large amounts of phycoerythrin appear red.

At one time it was believed that algae with specialized green-absorbing accessory pigments outcompeted green algae in deeper water. Some green algae, however, grow as well as other algae in deep water, and the deepest attached algae include green algae. The explanation of this paradox is that the cell structure of the deepwater green algae is designed to capture virtually all light, green or otherwise. Thus, while green-absorbing pigments are advantageous in deeper waters, evolutionary changes in cell structure can evidently compensate for the absence of these pigments.


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Engel, G.S. et al. Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems. Nature 446, 782–786 (2007).

Hildner, R., Brinks, D., Nieder, J.B., Cogdell, R.J. & van Hulst, N.F. Quantum coherent energy transfer over varying pathways in single light-harvesting complexes. Science 340, 1448–1451 (2013).

Collini, E. et al. Coherently wired light-harvesting in photosynthetic marine algae at ambient temperature. Nature 463, 644–647 (2010).

Tiwari, V., Peters, W.K. & Jonas, D.M. Electronic resonance with anticorrelated pigment vibrations drives photosynthetic energy transfer outside the adiabatic framework. Proc. Natl. Acad. Sci. USA 110, 1203–1208 (2013).

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Dostál, J. et al. Two-dimensional electronic spectroscopy reveals ultrafast energy diffusion in chlorosomes. J. Am. Chem. Soc. 134, 11611–11617 (2012).

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Brightness, Saturation and Hue

These are the three main qualities of light in relation to color. Brightness is the amount of light given off by a light source, usually expressed in lumens or lux. Some studies have shown that brighter light can intensify emotions, while low light doesn’t remove emotions, but keeps them steady. This can lead to people having the ability to make more rational decisions in low light and find it easier to agree with others in negotiation.

Saturation is the intensity of a color. More saturated hues can have amplifying effects on emotions, while muted colors can dampen emotions. In art, saturation is defined on a scale from pure color (100% [fully saturated]) to grey (0%). In lighting, a similar scale can apply.

Hue is defined as a color or shade. It’s been proven (through various studies) that natural light can make you happier, but colors created by artificial light can also evoke different emotions and have other effects on the body.

Blue/white light makes us energetic and can interrupt sleep patterns if exposed to around bedtime due to the fact that blue light suppresses melatonin levels. Brain cells tend to be the most sensitive to blue wavelengths and the least sensitive to red wavelengths. Blue wavelengths can even have an impact on those who are blind when it comes to circadian rhythms.

Red/amber light is the least likely hue of light to impact our internal clocks. Red light in the evening can help improve mental health. This is because red light in the evening helps increase the secretion of melatonin which leads to better sleep at night. Better sleep at night leads to improved cognition and overall mental wellbeing.


Site 2: Photolab

This simulation allows you to manipulate many variables. You already observed how light colors will affect the growth of a plant, in this simulation you can directly measure the rate of photosynthesis by counting the number of bubbles of oxygen that are released.

There are 3 other potential variables you could test with this simulation: amount of carbon dioxide, light intensity, and temperature. Keep the light settings at white light (you already tested colored light in the last experiment.)

Choose one variable and design and experiment that would test how this factor affects the rate of photosynthesis. Remember, that when designing an experiment, you need to keep all variables constant except the one you are testing. Collect data and write a summary of your findings that includes:


Does the light color spectrum and frequency matter for photosynthesis? - Biology

By 300 BC, Greek scholars had begun to study and contemplate optical phenomena generating theories to explain vision, color, light, and astronomical phenomena. Many of those theories turned out to be wrong, but they did serve to inaugurate the science of optics.

During the second century AD, Ptolemy , a Greek astronomer based in Alexandria, Egypt, studied and wrote about many topics in science. He published five books about optics, but only one book has survived to the modern era. This series of works was dedicated to the study of color, reflection, refraction, and mirrors of various shapes.

Few other advances were made in optics until after 1000 AD. The Arab scholar Alhazan , a.k.a. Abu Ali Hasan Ibn al-Haitham, conducted the first serious study of lenses in Basra (Iraq). He studied refraction in lenses, and also carried out research on reflections from spherical and parabolic mirrors. His writings were the first to explain vision correctly, as a phenomenon of light coming into the eye, rather than the eye emitting light rays.

Roger Bacon , an English philosopher from the 13th century, postulated, but could not demonstrate, that the colors of a rainbow are due to the reflection and refraction of sunlight through individual raindrops.

NOTE: The term “light” is often extended to adjacent wavelength ranges that the eye cannot detect - to infrared radiation, which has a frequency less than that of visible light, and to ultraviolet radiation, which have a frequency greater than that of visible light. This is the attitude employed by the editors of this page.

Newton’s Prism Experiments

Even before Newton’s famous experiments (1665) with light people were using prisms to experiment with colour, and thought that somehow the prism colored the light. Newton obtained a prism, and set up his so that a spot of sunlight fell onto it. Usually, in such experiments a screen was put close to the other side of the prism and the spot of light came out as a mixture of colour. Newton realised that to get a proper spectrum you needed to move the screen a lot further away.

After moving the screen and achieving a beautiful spectrum he did his crucial experiment to prove that the prism was not colouring the light. He put a screen in the way of his spectrum, and this screen had a slit cut in it, and only let the green light go through.

Then he put a second prism in the way of the green light. If it was the prism that was colouring the light, the green should come out a different colour. The pure green light remained green, unaffected by the second prism.

In another Experiment, after getting a spectrum with his prism, he placed another prism upside-down in the way of the light spectrum after passing the first prism. The band of colors combined again into white sunlight. For a demonstration of this experiment click here .

In these experiments, Newton had proved that white light was made up of colors mixed together, and the prism merely separated them - he was the first person to understand the rainbow.

William Herschel:The Discovery of Infrared Light

William Herschel (1738 - 1822) was one of the most important astronomers that ever lived. In 1800 he performed a famous experiment where he tried to measure the temperature of different colors of the spectrum by placing a thermometer on each colour. He found to his amazement that the hottest part of the spectrum was in a place where there was no colour at all. It was a spot beyond the red end of the spectrum. For the first time it was possible to talk about invisible light. This hot light became known as Infrared (below the red) because it was shown to have longer wavelength than visible light. Apart from its wavelength, Infrared has all the other properties of light.

Johann Ritter:The Discovery of Ultraviolet Light

After learning about William Herschel's discovery of infrared light, which he found beyond the visible red portion of the spectrum in 1800, Johann Ritter began to conduct experiments to see if he could detect invisible light beyond the violet portion of the spectrum as well. In 1801, he was experimenting with silver chloride, which turned black when exposed to light. He had heard that blue light caused a greater reaction in silver chloride than red light did. Ritter decided to measure the rate at which silver chloride reacted to the different colors of light. He directed sunlight through a glass prism to create a spectrum. He then placed silver chloride in each color of the spectrum and found that it showed little change in the red part of the spectrum, but darkened toward the violet end of the spectrum. Johann Ritter then decided to place silver chloride in the area just beyond the violet end of the spectrum, in a region where no sunlight was visible. To his amazement, this region showed the most intense reaction of all. This showed for the first time that an invisible form of light existed beyond the violet end of the visible spectrum. This new type of light, which Ritter called Chemical Rays, later became known as ultraviolet light or ultraviolet radiation (the word ultra means beyond).

BEWARE: Since this experiment involves the use of chemicals, it should be performed under the supervision of teachers or adults familiar with safety procedures.


Watch the video: 2 1 Η παραγωγή θρεπτικών ουσιών στα φυτά Η φωτοσύνθεση (January 2023).