• Home
  • /
  • Blog
  • /
  • Is sunlight the best spectrum for planting?

Is sunlight the best spectrum for planting?


November 9, 2023

Originally, it should not be a topic, but the industry that makes grow light still has continuous interpretations of this issue. In fact, this issue has been clearly demonstrated, and let's review it again here.

At present, there are several views on this issue:

  1. The sunlight spectrum is the spectrum with the highest photosynthesis efficiency, and the grow light should be equipped with a similar sunlight spectrum.
  2. Plants all over the world grow and evolve under sunlight, and the similar sunlight spectrum is the best spectrum for grow lights.
  3. The grow light with a similar sunlight spectrum can make plants grow the best. First, clarify a point of view.

The sunlight spectrum is the spectrum with the most complete spectral components.

Next, let's answer the three questions above.

  1. For plant photosynthesis, the sunlight spectrum is not the spectrum with the highest photosynthesis efficiency, which is why we need to study spectral technology.
  2. Plants around the world grow under different latitude light and climate and geographical conditions to adapt to sunlight. For plants, there is no best spectrum, only the most suitable.
  3. Compared with LED light sources, the biochemical indicators and nutritional indicators of plants growing under artificial light are no worse than those under sunlight, and some indicators are better controlled than under sunlight. To learn the spectral technology of biophotonics, you must first clarify the following cognition:

Photosynthesis is a synonym for plant light absorption.

Photosynthesis is a way to convert light energy into matter.

Einstein's mass-energy equation shows: energy is matter, and matter is also energy.

Light is colorless, and the light of different wavelengths is just the difference in photon energy.

Next, let's explain why?

1.Energy content of sunlight

Sunlight is the radiant (electromagnetic) energy of the sun. It provides light and heat to the earth and provides energy for photosynthesis. This radiant energy is essential for the biological environment and human metabolism. The solar radiation spectrum has three related wavelength ranges, namely: ultraviolet light, visible light (PAR: 400-700 nm) and infrared light.

Please note here: Far-Red and Infrared are not the same thing.

56% of the energy of solar radiation reaching the earth can reach the surface of the earth. However, some of the light is reflected by snow or other bright surfaces, so only 48% of the energy can be absorbed by land or water (note that the water surface also reflects part of the solar radiation)

Among the sunlight reaching the surface of the earth, infrared radiation accounts for 49.4%, and visible light accounts for 42.3%. Ultraviolet radiation only accounts for more than 8% of the total solar radiation. Each of these bands has different effects on the environment.

2.Spectrum required for photosynthesis

The band that sunlight can provide for photosynthesis is called photosynthetically active radiation PAR, and the band is: 400-700 nm. At present, science has not overturned this general knowledge.

UV-C includes wavelengths between 100 and 280 nm. This radiation range only accounts for 0.5% of all solar radiation, but it causes the most damage to organisms. However, most short-wave radiation is absorbed by stratospheric gases (ozone) and rarely reaches the surface.

Infrared light and ultraviolet light are located on both sides of the spectrum PAR.

Infrared light radiation has a wavelength >760 nm, providing 49.4% of solar energy. Infrared radiation is easily absorbed by water and carbon dioxide molecules and converted into heat energy. The wavelength of infrared light generates heat by exciting the electrons in the substance that absorbs them. Therefore, infrared radiation is responsible for warming the surface of the earth. Due to its longer wavelength, it reflects more than ultraviolet light or visible light. This reflection allows infrared radiation to transfer heat between surfaces, water and air.

In addition to UVC, only UVA and UVB ultraviolet light can reach the surface of the earth. The plant's absorption response to this part of the light is related to the plant's traits and is still under study. One thing is certain, the association between photosynthesis and this part of light energy is extremely low, or none.

3.Photosynthetic quantum efficiency

Photosynthesis mainly occurs in the leaves of plants, which contain the highest concentration of chloroplasts. The leaves of plants have tiny stomata, which absorb carbon dioxide from the surrounding air.

Chloroplasts contain chlorophyll, and the energy of chloroplasts is converted into chemical energy by absorbing solar energy. The other two components required for photosynthesis are carbon dioxide and water. The combination of these three substances provides energy for the photosynthesis process, thereby producing glucose and oxygen. Glucose provides available energy for plant growth.

The maximum efficiency of sunlight for photosynthesis can be explained from the quantity.

For the light energy of the PAR band, the average wavelength is 570 nm; therefore, the light energy used in the photosynthesis process is about 50 cal per nanometer.

Usually, the number of photons absorbed for each released oxygen molecule, called the quantum requirement.

The quantum requirement is usually 8-12 photons (PAR energy), we calculate with 9 photons, the photon energy used is 9 × 50=450 cal, that is, 450 cal is required for each release of 1 oxygen molecule.

The energy stored for each release of oxygen is 117 cal, and the estimated maximum energy efficiency of photosynthesis is 117/450=0.26, which is 26%. This is the theoretical maximum value for the conversion of light energy into matter.

In fact, various factors reduce this efficiency, such as temperature, humidity, light inhibition, assimilation energy conversion efficiency, Calvin cycle efficiency, water, nutrients, etc. Considering various factors, the recorded typical photosynthesis efficiency The maximum value is about 12%, which means that the energy efficiency stored in plants through photosynthesis is up to 12% of the PAR part of sunlight.

And the photosynthetic quantum efficiency of artificial light with spectral technology is much larger than that of the solar spectrum, which can be calculated.

Photosynthesis only uses a small part of the incident sunlight (PAR) to transform into organic compounds. The average net carbon fixation efficiency of terrestrial plants is only 3.3%, and most plants have low utilization efficiency of sunlight.

The conclusion is: The photosynthetic efficiency of the solar spectrum is lower than that of the artificially matched grow light spectrum, because many energies in the spectral components are wasted.

4.Nutritional composition and taste of edible parts of plants

Here, someone may propose that the nutrition and taste of plants under the sunlight spectrum are good. I think that people who hold this view must provide repeatable experimental data, such as biochemical indicators and nutritional composition indicators. From the mechanism of plant light energy absorption, the traits of plants under the two energy supplies of sunlight and artificial light will not be different. The only difference is the time integration effect and stress effect.

Given the same planting environment and light level, the nutritional composition and taste of the edible part of the plant will not be different, because the plant cannot distinguish between sunlight and artificial light at all. It is not scientific to compare fast-growing and slow-growing plants, because some substances that affect the taste of plants need time effect to accumulate.

5.Need to follow scientific experimental methods to explain

For the comparative study of photosynthesis of sunlight and artificial light, the more systematic study is the experiment of American scientist Mokley. For this part of knowledge, you can see the WeChat public: fsourled, there are introductions to Mokley's research articles, you can see it by searching in the public account.

Mokley's research shows that the efficiency of plant utilization of light energy is reflected in the spectral form, and the spectral form is the basis for the design of artificial light spectrum. Spectral technology provides the lowest energy consumption spectral ratio (formula), and this ratio is not based on the solar spectrum, but based on the demand properties of plant light energy.

6.The purpose of plant spectral technology research

Any technological advancement, its essence is to improve application efficiency, and plant artificial light technology is also this purpose. In the greenhouse and plant factory environment, due to the lack of natural light energy supply, it has triggered the application of artificial light, and artificial light has proposed spectral technology based on the absorption properties of plants to light. Through application, it is found that artificial light can completely replace natural light, and at the same time, the planting efficiency is greatly improved, which conforms to the transformation process of agricultural planting industrialization. The purpose of studying spectral technology is to improve planting efficiency, so we must study spectral technology based on the properties of plant light absorption, rather than studying based on the solar spectrum. The mechanism of photosynthesis and other mechanisms of plants are the same, with its occurrence, growth and aging process. The photosynthesis rate is low in the early stage of development; it is high after growth and stabilizes for a period of time; it decreases when it is old. The physiological state of the plant and external conditions have a significant impact on the duration and height of each stage of the photosynthesis rate. When other parts of the plant increase the demand for photosynthetic products, the photosynthesis rate often increases. On the contrary, when the utilization of photosynthetic products slows down or the output is blocked, the photosynthesis rate will gradually decrease.

Through the spectral technology of artificial light, it can well meet these absorption characteristics of plants and provide the highest planting efficiency to the greatest extent. This is another purpose of the research on grow light spectral technology.

7.Grow light spectral technology advocates full use of sunlight

The application of grow light spectral technology has never excluded the full use of sunlight, and their relationship is more closely linked under the effect of market economy.

An excellent spectral technology is a technical performance based on the maximum use of sunlight.

Here, reiterate a principle:

There is no best spectrum, only the most suitable.

About the author

TUBU is an expert in LED light research with more than 10 years of experience in this field. We hope that through our TUBU research, LED lighting technology will become more popular and bring greater convenience and comfort to people's lives.

{"email":"Email address invalid","url":"Website address invalid","required":"Required field missing"}

Never miss a good story!

 Subscribe to our newsletter to keep up with the latest trends!