How Do Leaves Look Like When Grown in Blue Light Only

What type of light does plants need?

Horticultural lighting differs significantly from lighting for humanity.
For example, the human eye perceives colors; plants instead have specific receptors for different wavelengths. Knowing that the correlation between the various wavelengths and its metabolic responses allow the plant-grower to affect the characteristics of a plant; such as biomass, form, nutritional values, taste, and timing of flowering.

FAR RED
Far-Red light is useful to influence seed germination for some species.
In nature a high concentration of Far-red radiation communicates to the seed in a shady environment and therefore will have less chance to sprout. It can therefore be used to select seeds with the strongest and most resistant characters, or to induce sprouting for plants grown in the wild environments without direct exposure to sunlight.
The Photo-Red and Far-Red ratio also leave impacts on the vegetative growth of plants.
High amounts of Far-Red light can cause stems and leaves to stretch. This is because the plant is trying to stretch in order to reach more sunlight.
High amounts of Far-Red light can also reduce the amount of chlorophyll, anthocyanins and antioxidants inside the plant. Chlorophylls and anthocyanins are pigments that make a plant colorful and affect the quality of the crop. Antioxidants instead protect plants against harmful free radicals.
In general, this frequency is useful to regulate and manage the "stretching" of the plant.
Plants associate the Far-Red spectrum in the shade, flowers are the reproductive tissues of a plant and if one thinks there is a risk for a plant of death (caused by a too shady environment), it will start to reproduce as soon as possible so as to pass his genetics to the offspring.
High amounts of spectrum Far-Red triggers and accelerates the flowering of various species, to name but a few: tomatoes, potatoes, cucumbers, beans, wheat, mustard and many ornamental flowers. In some species it increases the number of flowers produced.

PHOTO RED
The Photo-red spectrum (660nm) corresponds to an absorption peak of chlorophyll, responsible for photosynthesis.
For this reason, in general, red light, who increases the rate of photosynthesis, is one of the spectra with the highest metabolic response from plants.
Although a plant can be grown using only red light, most plants have better growth with a wider spectrum of light. Furthermore, plants grown under red light alone may not have anticipated characteristics. For example, plants grown with only red light can have thin and stretched stems with sparse leaves.
Both red and blue light are absorbed more efficiently by photosynthetic pigments than lights from other regions of the spectrum. The red-blue combination allows a greater speed of photosynthesis compared to red or blue light solely. Compared to the red light alone, the combination of red-blue lights also increases the size of the plant, the quantity of leaves, the size of the leaves, the chlorophyll content and, in general, facilitates a more poiced and integrate development.
Red light is the key to vegetative growth, the addition of blue light and those from other wavelengths further increase the rate of photosynthesis and plant size.
The Photo-Red spectrum affects flowering by two means. Firstly, red light is important for photosynthesis, thus it is essential for a flourishing bloom. Secondly, the red light mediates flowering timing in some species.
The flowering process requires extremely high energy-supply, and there is a strong correlation between the size of the plant (eg vegetative growth) and the size of the flower. Therefore, a plant with high photosynthesis volume will accumulate more resources which will later facilitates itself to flourish.

GREEN
The green component plays a role in photosynthesis and vegetative growth because it is inside the range of photosynthetically active radiation. However, its impact on the growth and development of plants isn't well understood by public as that of red or blue.
Plants reflect green light, which is why they appear green to our eyes. This may lead us to think that green light is not used by plants. However, only about 5-10% of the green light is reflected from a plant and the rest (90-95%) is absorbed or transmitted to the lower leaves.
When combined with red and blue light, the green spectrum further increases plant growth. But over usage of green light (over 50% of total light) can lead to counteraction of plant growth.
Green light is easily transmitted through the leaves. This means that the leaves in the lower part of the foliage receive an altered spectrum that is fainted in blue and red and augmented in green.
In many plants, flowering is mainly regulated by two key photoreceptors: cryptochrome and phytochrome. Both photoreceptors respond primarily to blue and red light, but can also respond to green light.
Green light is effective in accelerating flowering in a certain number of species. Once flowering began, it is important to provide plants with a "full spectrum" light that has high volume of blue, red and green light in order to optimize photosynthesis.
When used together with red and blue light, green is important for vegetative, germinative and flowering growth phases. Green light penetrates the foliage of the plant, allowing light to reach the lower branches of the plant. Green light can also be used to manipulate the stomatal opening and closure and the height of the plant. In some species, green light can even regulate seed germination and flowering. The addition of other light colors (full spectrum light) has been shown to have additional benefits for plant growth.

BLUE
The Royal blue spectrum (450nm) corresponds to an absorption peak of chlorophyll, responsible for photosynthesis. However, blue light is less effective than red light to stimulate photosynthesis. This is because blue light can be absorbed by low-efficiency pigments such as carotenoids and inactive pigments like anthocyanins. Surprisingly, when some species are grown with merely blue light, plant biomass (weight) and photosynthesis rate are similar to those of a plant grown with only red light.
In addition to playing an important role in photosynthesis, blue light is well known for suppressing the "stretching" of the stem. Stem stretch occurs when a plant receives insufficient light and extends to capture more light. Plants grown with blue light are generally shorter and have thicker and denser leaves than those grown without blue light. This is attributed to the action of cryptochrome, which responds to blue light to control different aspects of plant growth and development, including stem lengthening.
In addition to controlling the bud size, a grower may want to check the flowering time. Through the action of cryptochrome, blue light is a strong regulator of flowering time. For long-day plants, blue light can enhance flowering, and for short day ones, it can restrain flowering.
Blue light is essential for both vegetative and flowering stages of plant growth. Blue light should be used in combination with red light to increase photosynthesis and implant size. The addition of other light colors, like the green one, has been shown to have additional benefits for plant growth. For this reason, 'full spectrum' lights usually lead to better risults with monochrome or two-color lights. The blue light is a strong regulator of plant height and flowering. In general, blue light makes the plants more compact, making the stems shorter and thicker.
Ultimately, the Photo-red (660nm) and Royal-blue (450) nm spectrum represent those with the greatest impact on the metabolic activity of a plant.

Therefore, it must be considered that the healthy and balanced growth of a plant requires much more complex interactions, which are catalyzed by different wavelengths.
In situations of artificial integration with natural light, the power can be concentrated in a calculated way, in the spectra that we would like to integrate according to the desired result.
Instead, in case artificial lighting is the only light source, the use of complete spectra is strongly recommended, in order to provide the plant with everything that can be used for a balanced and complete development.

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Source: https://www.orizzonteled.com/en/what-type-of-light-does-plants-need/

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