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The study and understanding of the interrelation of optical radiation and plants, seeds and soil is critically important for our existence. Research and control of biochemical factors require a precise and predictable measurement technology.
The absorption of optical radiation in the range of wavelengths between 300 nm and 930 nm initiates photochemical reactions in plants that are essential for plant growth. The three most important reactions of plants to optical radiation are: Photosynthesis, Phototropism, Photomorphogenesis
Photosynthesis
Photosynthesis is one of the most important biochemical processes on the planet. In the process of photosynthesis green plants absorb carbon dioxide from the atmosphere and water from the soil, combining them with the aid of radiation energy to build sugar, releasing oxygen and water into the atmosphere. This process can be described by the following assimilation formula:
The occurrence of photosynthesis in plants is characterized by the green color of their leaves. This is due to chlorophyll which is absorbed with the photosynthetically active radiation. Accordingly, the absorption of the quanta of radiation energy in the chlorophyll molecules raises the electrons to a higher energy state. As they return to their initial state, the energy released is converted into chemical energy.
In general plant physiology, the term Photosynthetically Active Radiation (PAR) refers to the radiation in the range of wavelengths between 400 nm and 720 nm. This is the energy that is absorbed by the assimilation pigments in blue-green algae, green algae and higher order plants. The wavelengths for the lower limit (400 nm) and an upper limit (720 nm) are not entirely rigid. Photosynthetic reactions have, for example, been established in some algae at wavelengths shorter than 400 nm. In general, the lower limit depends on the structure and the thickness of the leaf as well as on the chlorophyll content. Some research projects have shown 700 nm as the upper wavelength limit.
In DIN 5031, Part 10 (currently in the draft phase) the spectral response function for photosynthesis is defined, and this is illustrated graphically below. For plant physiology, this range can be divided into three narrower bands:
- 400 nm to 510 nm: strong light absorption by chlorophyll, high morphogenetic effect
- 510 nm to 610 nm: weak light absorption by chlorophyll, no morphogenetic effect
- 610 nm to 720 nm: strong light absorption by chlorophyll, high morphogenetic and ontogenetic effect
This response function can be considered as a mean spectral response function. A number of different investigations have shown that the spectral absorption spectra of various plant types can be very different. These differences can also occur, in a single plant, e.g. in leaves of different ages or with different thicknesses, chlorophyll content, etc.. It should also be noted that the spectral response function for photosynthesis is defined with avoidance of mutual cell shading, experimenting with a young, thin leaf or with a thin layer of algae suspension.
The absorption of optical radiation in the range of wavelengths between 300 nm and 930 nm initiates photochemical reactions in plants that are essential for plant growth. The three most important reactions of plants to optical radiation are: Photosynthesis, Phototropism, Photomorphogenesis
Photosynthesis
Photosynthesis is one of the most important biochemical processes on the planet. In the process of photosynthesis green plants absorb carbon dioxide from the atmosphere and water from the soil, combining them with the aid of radiation energy to build sugar, releasing oxygen and water into the atmosphere. This process can be described by the following assimilation formula:
The occurrence of photosynthesis in plants is characterized by the green color of their leaves. This is due to chlorophyll which is absorbed with the photosynthetically active radiation. Accordingly, the absorption of the quanta of radiation energy in the chlorophyll molecules raises the electrons to a higher energy state. As they return to their initial state, the energy released is converted into chemical energy.
In general plant physiology, the term Photosynthetically Active Radiation (PAR) refers to the radiation in the range of wavelengths between 400 nm and 720 nm. This is the energy that is absorbed by the assimilation pigments in blue-green algae, green algae and higher order plants. The wavelengths for the lower limit (400 nm) and an upper limit (720 nm) are not entirely rigid. Photosynthetic reactions have, for example, been established in some algae at wavelengths shorter than 400 nm. In general, the lower limit depends on the structure and the thickness of the leaf as well as on the chlorophyll content. Some research projects have shown 700 nm as the upper wavelength limit.
In DIN 5031, Part 10 (currently in the draft phase) the spectral response function for photosynthesis is defined, and this is illustrated graphically below. For plant physiology, this range can be divided into three narrower bands:
- 400 nm to 510 nm: strong light absorption by chlorophyll, high morphogenetic effect
- 510 nm to 610 nm: weak light absorption by chlorophyll, no morphogenetic effect
- 610 nm to 720 nm: strong light absorption by chlorophyll, high morphogenetic and ontogenetic effect
This response function can be considered as a mean spectral response function. A number of different investigations have shown that the spectral absorption spectra of various plant types can be very different. These differences can also occur, in a single plant, e.g. in leaves of different ages or with different thicknesses, chlorophyll content, etc.. It should also be noted that the spectral response function for photosynthesis is defined with avoidance of mutual cell shading, experimenting with a young, thin leaf or with a thin layer of algae suspension.
