Nederhoff (2000) pointed out that LED is a promising technology for greenhouse lighting, which is more efficient and feasible than HPS. The photoelectric conversion efficiency of some LEDs is higher than that of HPS and is still improving. Also, red light is higher than HPS lamps in activating plant photosynthesis. LEDs have special light qualities that can activate specific plant effects, or control plant processes and plant balance (morphogenetic effects).
In the Netherlands, LEDs improve energy efficiency. Related research in the Netherlands shows that it is feasible to use LEDs in the production of winter fruit vegetables, salad plants (especially lettuce), medicinal plants, cut flowers and ornamental plants.
According to the way the lamps are hung and the direction of illumination, as well as the relative positional relationship between the LED light source and the lamps and the canopy, the greenhouse lighting technology is divided into top lighting, top lighting, and interlighting. , Canopy fill light, (landing) vertical side fill light and three-dimensional multi-layer lighting system (muli-layer systems) six categories.
Greenhouse HPS lighting is usually installed on the top of the greenhouse, more than 1.5m from the top of the crop, to prevent high temperature from burning plants, because LEDs do not generate radiant heat and can be illuminated close to plants. The inter-row fill light means that the LED lights are placed between the plants, and the height is in the position of the leaf group with higher photosynthetic activity, and the light efficiency is increased. Under light conditions, the lower leaves of the crop can remain active for a longer time. Moreover, the air-cooled LED lamp is placed among the plants and the heat released can heat the plants.
HPS lamps release heat to warm plants to stimulate leaf respiration, and conversely, respiration cools leaves, so the temperature of plant leaves under HPS lamps can be lower, equal to or higher than the ambient air temperature. Respiration is higher under HPS lights and lowest under water-cooled top fill LED lights. Holland standard lamp installation, light intensity is 80～120umo/m2·s, the maximum is 200umol/m2·s.
There are differences in illumination and leaf angle between different supplementary lighting methods. In the past ten years, many studies have focused on comparing the differences in energy saving and crop response effects between different types of supplementary light sources, between different blue light ratios, and among supplementary light methods.
Canopy top fill light technology
With the help of the characteristics of the downward cold light source of the LED light source, the LED lamps are suspended in the upper part of the canopy parallel to the horizontal plane of the canopy, and the upper surface of the canopy is illuminated vertically. This method is suitable for greenhouse production methods with thin canopy, high density, and relatively uniform upper surface of the canopy, such as seedling raising and leafy vegetable production. Since the LED cold light source can illuminate the plants at a close distance, the LED light can be placed at a closer distance above the canopy.
At present, LED lights can be installed directly above the crop canopy through cultivation devices such as culture racks (Zhang Liwei et al., 2010), hydroponic layer racks (Li Wenlin et al., 2010), or movable light racks (Wu Jiasen et al., 2009). Increasing photosynthesis DLI (photosynthetic daily light integral) at seedling stage improves the growth and flowering of flower bed plant seedlings. The effects of increasing DLI on plant and subsequent growth and development at different stages of seedling raising (Oh et al., 2010).
Interrow canopy fill light technology
The inter-row canopy supplementary light technology is to place the LED light at the height of the canopy between the two rows of the crop, and design bidirectional or unidirectional illumination of the canopy photosynthetically active leaf group through a specific light-emitting angle. The irradiation angle should be as vertical as possible to the leaves to increase the level of intercepted light intensity. This method is suitable for use with bidirectional LED lamps. This technology is suitable for greenhouse production of tall fruits and vegetables, such as tomatoes, cucumbers, etc., which can maximize the photosynthetic capacity of photosynthetic active leaf groups and transport them to growing points and fruits in a short distance.
Henández and Kubota (2012) studied the effect of LED inter-row fill light with different spectrums on greenhouse mini cucumbers. The top fill light intensity (145umol/m2 s, PAR) was provided by HPS. 3 kinds of LED fill light spectrum are red light, blue light and white light LEDs, 14.5umol/m2·s, only 10% of the top fill light.
All LED supplementary light improves the appearance quality of the fruit, and also increases the fruit yield in the early stage, but the yield-increasing effect disappears in the later stage. Smaller crop canopy and canopy densities (on LED supplemental light systems) reduce light interception and reduce beneficial benefits.
Greenhouse Lighting Technology
Nederhoff (2000) pointed out that LED is a promising technology for greenhouse lighting, which is more efficient and feasible than HPS. The photoelectric conversion efficiency of some LEDs is higher than that of HPS and is still improving. Also, red light is higher than HPS lamps in activating plant photosynthesis. LEDs have special light qualities that can activate specific plant effects, or control plant processes and plant balance (morphogenetic effects).
In the Netherlands, LEDs improve energy efficiency. Related research in the Netherlands shows that it is feasible to use LEDs in the production of winter fruit vegetables, salad plants (especially lettuce), medicinal plants, cut flowers and ornamental plants.
According to the way the lamps are hung and the direction of illumination, as well as the relative positional relationship between the LED light source and the lamps and the canopy, the greenhouse lighting technology is divided into top lighting, top lighting, and interlighting. , Canopy fill light, (landing) vertical side fill light and three-dimensional multi-layer lighting system (muli-layer systems) six categories.
Greenhouse HPS lighting is usually installed on the top of the greenhouse, more than 1.5m from the top of the crop, to prevent high temperature from burning plants, because LEDs do not generate radiant heat and can be illuminated close to plants. The inter-row fill light means that the LED lights are placed between the plants, and the height is in the position of the leaf group with higher photosynthetic activity, and the light efficiency is increased. Under light conditions, the lower leaves of the crop can remain active for a longer time. Moreover, the air-cooled LED lamp is placed among the plants and the heat released can heat the plants.
HPS lamps release heat to warm plants to stimulate leaf respiration, and conversely, respiration cools leaves, so the temperature of plant leaves under HPS lamps can be lower, equal to or higher than the ambient air temperature. Respiration is higher under HPS lights and lowest under water-cooled top fill LED lights. Holland standard lamp installation, light intensity is 80～120umo/m2·s, the maximum is 200umol/m2·s.
There are differences in illumination and leaf angle between different supplementary lighting methods. In the past ten years, many studies have focused on comparing the differences in energy saving and crop response effects between different types of supplementary light sources, between different blue light ratios, and among supplementary light methods.
Canopy top fill light technology
With the help of the characteristics of the downward cold light source of the LED light source, the LED lamps are suspended in the upper part of the canopy parallel to the horizontal plane of the canopy, and the upper surface of the canopy is illuminated vertically. This method is suitable for greenhouse production methods with thin canopy, high density, and relatively uniform upper surface of the canopy, such as seedling raising and leafy vegetable production. Since the LED cold light source can illuminate the plants at a close distance, the LED light can be placed at a closer distance above the canopy.
At present, LED lights can be installed directly above the crop canopy through cultivation devices such as culture racks (Zhang Liwei et al., 2010), hydroponic layer racks (Li Wenlin et al., 2010), or movable light racks (Wu Jiasen et al., 2009). Increasing photosynthesis DLI (photosynthetic daily light integral) at seedling stage improves the growth and flowering of flower bed plant seedlings. The effects of increasing DLI on plant and subsequent growth and development at different stages of seedling raising (Oh et al., 2010).
Interrow canopy fill light technology
The inter-row canopy supplementary light technology is to place the LED light at the height of the canopy between the two rows of the crop, and design bidirectional or unidirectional illumination of the canopy photosynthetically active leaf group through a specific light-emitting angle. The irradiation angle should be as vertical as possible to the leaves to increase the level of intercepted light intensity. This method is suitable for use with bidirectional LED lamps. This technology is suitable for greenhouse production of tall fruits and vegetables, such as tomatoes, cucumbers, etc., which can maximize the photosynthetic capacity of photosynthetic active leaf groups and transport them to growing points and fruits in a short distance.
Henández and Kubota (2012) studied the effect of LED inter-row fill light with different spectrums on greenhouse mini cucumbers. The top fill light intensity (145umol/m2 s, PAR) was provided by HPS. 3 kinds of LED fill light spectrum are red light, blue light and white light LEDs, 14.5umol/m2·s, only 10% of the top fill light.
All LED supplementary light improves the appearance quality of the fruit, and also increases the fruit yield in the early stage, but the yield-increasing effect disappears in the later stage. Smaller crop canopy and canopy densities (on LED supplemental light systems) reduce light interception and reduce beneficial benefits.