The use of more and more popular LEDs to provide the right amount of light to plants is today the best possible solution for plant lighting. It is a highly practical solution, because LED technology allows us to precisely control factors such as the duration of the illumination (photoperiodism), the intensity and color temperature of the light, the distance of the radiation source and the angle of incidence of the light rays, as well as the length of the light waves (known). Plants react to light differently depending on the length of its ray, which is the result of the evolution of plants under different lighting conditions. Under natural conditions, the spectral distribution of light depends on latitude and the season. There may also be factors at stake, such as the change in the position of the light source and the movement of the plant in response to this fact, i.e. phototropism. The use of LEDs is becoming especially popular among people who need lighting on an industrial scale or simply cultivating plants, especially exotic ones. Universal configurations are sometimes acceptable here, but creating ideal conditions for the plant requires preparing a configuration adapted to their specific requirements, taking into account the periods of use of lighting and taking care of the appropriate light intensity. Theoretical background when deciding to use artificial lighting for plants, it is necessary to have a basic knowledge of the properties of light.
Color temperature
An objective measure that describes what we perceive as the color of a light source. It is described in degrees Kelvin. A typical daylight on a cloudy day will have a temperature above 8000K, and a burning campfire will have a temperature below 1000K. Plants can expect light temperatures as low as around 2000K (sunrise and sunset conditions) and up to 5500K and more for typical daytime conditions.
The color of the wavelength
The color of a given light wave, i.e. the color obtained by a given part of the electromagnetic wave of white light after it has been split. Each length of light that makes up white light has its own characteristic color, and basically it is perceived by us as a specific color. LEDs are able to produce light of different wavelengths, that is, which we see as different colors. Plants are adapted to the use of light, the wave of which is most often in the visible spectrum, so that most lighting configurations will be seen by us simply as white light. * Note: A clear distinction must be made here between the color temperature and the color of the wavelength. The color temperature is our impression of light, related to, among others, with its dispersion. Light of a different color can have a different color temperature and this is our feeling, which can still be objectively measured. The color of light is a physical property of it is determined by its wavelength. Plants require light of the right color and color temperature.
The wavelength of the radiation
The wavelength of light can be measured. The measurement results are usually given in graphical form as a spectral distribution of light which plots the number of wavelengths of a given length in the light beam. Virtually always the light we see consists of wavelengths of different lengths and can be tinted with the dominant color. Even seemingly single-color LEDs will shine with a whole range of different colors of light, i.e. they will emit light of different wavelengths, although one light color will be very dominant, which is a great advantage of this technology. White light is light that combines all the colors of the spectrum visible to humans. Plants may also require light that is invisible to humans.
The wavelength of radiation needed by plants
How much energy is transferred by the wavelength depends on the wavelength. Shorter wavelengths carry more energy than longer wavelengths. Plants are adapted to catch wavelengths of a certain length, because their photosynthesis process is adapted to obtain fuel with specific properties. This is an evolutionary effect. Plant preferences are measured and presented as the energy distribution of photosynthetic radiation, that is, it shows what light is actually used by the plants. Light plants need light actively photosynthetically
Photomorphogenesis
The process of plant growth due to the use of sunlight takes place thanks to photosynthesis, i.e. the production of nutrients from simple substances and solar energy. Solar energy must be properly absorbed by plants. The important thing is that plants "see" sunlight differently than humans. Sunlight is a very wide range of radiation from very short ultraviolet waves to very short infrared waves. The human eye sees best green colors with a length of 500-600 nanometers, and it is worse at shorter and longer radiation. For plants, this radiation is the least useful. Plants are mostly green in color because they reflect most green light and absorb blue and purple light, as well as higher energy red and infrared light. Some of these waves are completely invisible to humans. LED lighting for plants is completed by combining diodes that offer the length of photosynthetically active light, taking into account the requirements of specific plants. The predominant diode is deep red ("dark red") which offers red light with a wavelength of 660 nm. It is a high-energy light that provides chlorophyll with large amounts of energy.
The spectrum of light for plants
Plants use different wavelengths (colors) in different ways and therefore it is necessary to combine them appropriately, taking into account also secondary factors, such as the exposure time that controls the rhythm of growth and flowering. Below is a brief description of the colors and their typical share in standard lighting system configurations. Blue (20-25%) - absorbed easily and in large amounts. Red (50-75%) - stimulates germination, bud development and flowering. Green (5-10%) - mostly reflected. Useful in the system for the correct visual assessment of the condition of plants. Ultraviolet (5%) - thickens the leaves, protects against pests and facilitates the care of the plant. Infrared (0-5%) - red light supplementation during the flowering period. The key colors here are mainly dark red, which is about half of the mixture, and red, which together with blue and the so-called royal blue each account for about 20% of the total amount of energy supplied to the plant. Infrared is an additional dose of energy useful in certain conditions, and green is a color that is needed mainly by a grower who will see the plant in a light close to natural.
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