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LED plant lighting technology to consider what factors are

Enterprises in the assessment of gardening lighting when the light will face multiple considerations, including: light intensity, spectrum, light distribution uniformity, energy efficiency and lamp life. Gardening lighting systems can convert electrical energy into light for plant growth and development, and photosynthesis-based light, while LED-based light sources provide tuned spectrum for applications.
However, determining the efficiency or performance of such solid state lighting (SSL) systems is a challenge. There are several factors that affect the overall efficiency of the lighting system. This article discusses how lighting design will affect energy efficiency and how energy efficiency in turn affects the overall profitability of controlled plant growth environments.
In fact, the effectiveness of gardening fixtures converting electrical energy into usable light for plant growth is critical to the success of controlled environmental agriculture (CEA). Figure 1 shows a vertical farm example for controlled environmental agriculture (CEA).
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The installation of lighting solutions within a few inches of the crop canopy is a breakthrough in vertical agricultural applications. Compared to poorly designed LED solutions and other lighting technologies such as HPS and Fluorescent, the correct design of the LED solution achieves higher throughput per square foot.
Gardening related indicators
The plant is mainly used for photosynthesis with visible light at a wavelength of 400-700 nm (hence, this section is also commonly referred to as photoprotective effective radiation (PAR), and the photosynthetic photon flux (PPF) measures the total amount of PAR generated per second in the illumination system. In the measurement, an integrating sphere is used to capture and measure almost all of the photons emitted by the illumination system. The unit of PPF is the number of moles per square meter per second of photons (μmol / s).
Photosynthetic photon flux density (PPFD) measures the amount of PAR reaching the canopy of the plant. PPFD represents the number of light quantum per unit time in the visible wavelength range, in μmol / m2 / s. PPFD also indicates the correlation between the number of photons and photosynthesis.
Finally, we discuss photon effects. Photon efficiency refers to the efficiency of the horticultural lighting system converting electrical energy into PAR photons. If the PPF of the light is known to the input power, the photon effect of the gardening lighting system can be easily calculated. The unit of measurement of PPF is μmol / s, and the unit of measurement watts is J / s per second, and the number of seconds in the numerator and denominator is eliminated, and the unit is μmol / J. This unit is used to express the effect. The higher the number, the more effective the lighting system converts electric energy into PAR photons.
A common method of gardening lighting
Next, we have to understand the nuances of lighting design, as well as the reasons for energy saving garden lighting system. The world's most commonly used gardening lighting system is based on high intensity discharge (HID) lighting and high pressure sodium (HPS). High pressure sodium lamps were originally designed specifically for planting plants and were designed for light rail and parking garage. However, ready availability and high output levels are widely used in horticulture because they provide very high light intensity, and most of the emitted light is in the range of 565-700 nm, and this effective band can accelerate photosynthesis.
One drawback of using gaseous lighting with high pressure sodium lamps is the generation of large amounts of radiant heat. The surface temperature of the high pressure sodium lamp can reach temperatures above 800 ° F (about 430 ° C), so there must be a sufficient distance between the plant canopy and the high pressure sodium lamp to avoid damage to the plant tissue. When the height of the fixture is increased, the anti-squaring law begins to function, which reduces the illumination rate. With the passage of time, the energy efficiency of high pressure sodium lamp increases, and the emergence of double-ended HPS lamps, can achieve 1.7μmol / J photon efficiency.
Turn to LED
We look at the LED in the use of gardening lighting process. In 2014, the most efficient LED gardening lighting system and double-ended high pressure sodium lamp efficiency. Compared with the high pressure sodium lamp, LED long life (L70 ≥ 50,000 hours) so many growers turn to use LED. However, compared with the high pressure sodium lamp, LED gardening lighting system cost is relatively high, limiting the transition to the LED lights.
LED chip manufacturers in the past few years has improved the effectiveness of existing components, so that they can significantly improve photon performance, and continue to improve every year. In fact, LED-based gardening lighting systems are now able to achieve 45% greater photon efficiency than double-ended high-pressure sodium lamps. Although the efficiency of a single component increases the efficiency of LED gardening lighting, it is only a variable that exceeds the high pressure sodium lamp technology.
LED system heat
When it comes to the heat generated by LED lighting, there is a common misunderstanding. Many growers believe that LEDs produce less heat than high-pressure sodium lamps, which are true when LEDs are driven at lower wattage. If there is a 600W LED lamp and a 600W double-ended high-pressure sodium lamp, from a macro point of view, they produce heat in the same approximate range.
LED and high pressure sodium lamp is the main difference between the two 600W produced PAR energy how much heat how to distribute from the lamps. Most of the heat from the high-pressure gas lamp is radiated down to the crop canopy, and most of the heat of the LED is generated at the connection of the part to the printed circuit board (PCB), which is usually conducted to the PCB, or it may be heat And removed by upward convection.
As a result, one of the main advantages of LEDs as a gardening lighting system is the ability to place plants near plants and protect plants from thermal radiation. However, if the heat is not effectively removed from the PCB by the appropriate thermal management system, the life of the LED assembly will be significantly reduced.
There are two ways to cool a lighting system in a commercial horticultural environment. Passive cooling lamps use heat sinks to dissipate heat from the circuit board, while active cooling lamps rely on fans or water to dissipate heat. The fan used to cool the lamp consumes energy and reduces the overall photon performance of the fixture. Also, if the fan fails during lamp operation, the LEDs on the PCB may overheat and burn out. Even if they do not have catastrophic failure, the reduced power output will greatly reduce the life of LED lamps. This is a very important factor that growers need to consider when comparing horticultural lighting systems.
Spectrum and efficacy
Another important factor influencing the photon function of the gardening system is the luminescence spectrum. The most efficient wavelengths for horticultural lighting systems are red (660 nm) and blue (450 nm). The traditional LED gardening lighting technology mainly uses the red band with a smaller proportion of the blue LED to achieve the highest photon performance.
Although the red LED has the highest photon performance, the plant does not grow itself at narrow wavelengths. Thus, in optimizing plant growth and development, a single red LED does not produce the most efficient spectrum. This is especially true when using single source lighting in vertical farms compared to supplementing greenhouse lighting (Figure 3).
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Poor and dirty environments (such as the greenhouse) may quickly cause the active cooling system to malfunction, resulting in failure of the entire lighting system. In addition to improving energy efficiency, the passive cooling system does not require moving parts that are easily broken and clogged.
Many gardening lighting manufacturers claim that their products have "special spectra" based on the absorption peaks of chlorophyll a and b. However, they did not mention that these chlorophyll pigments were extracted from plant leaves and measured in vitro. The effect of light mass on photosynthesis (Figure 2) was proposed by McCree and Inada in the 1970s. Studies have shown that the photosynthetic rate is correlated with the action spectra of chlorophyll a and b, but they are not the only wavelengths for photosynthesis. Prior to this study, there was a common misconception that chlorophyll mainly absorbed the red and blue parts of the visible spectrum, so plant photosynthesis did not use green light.
Studies conducted by McCree and Inada are the basis for understanding the effect of spectral light on photosynthesis; however, they have developed a spectrum of photosynthesis based on photosynthesis at low light intensity. In the past 30 years, there have been many studies on plant photosynthesis at higher light intensities, indicating that the effect of spectral quality on growth rate is much less than that of light intensity.
Spectral light quality has a significant effect on plant development, such as seed germination, stem elongation and flowering, as well as secondary metabolites and flavonoids, which affect the taste, appearance and odor of plants. Therefore, LED manufacturers need to use the most efficient LED and the growers hope to promote the best growth and development of plants between the LED to find a balance between.
Shape factor and beam control
We finally discussed a theme related to the shape of the fixture, beam optical and light intensity. Considering the overall efficiency of the gardening lighting system, you need to consider PPFD and CU. However, although the photon effect of the fixture itself is very important for gardening lighting, the real energy efficiency of the scheme will be greatly reduced if the light produced in practical applications is not uniformly and effectively photographed on the crop.
Because each high pressure sodium lamp has only one light source (360 ° bulb), it is necessary to rely on the reflector to spread the light evenly on the canopy of the crop. Another advantage of LEDs over high-pressure gas lamps is that hundreds of light sources can form a very uniform light band through custom beam optics without the use of reflectors. Figure 4 depicts a typical LED light engine.
The spectrum of light emitted from the gardening system (ie, color) has a significant effect on energy efficiency and the overall plant growth and development. Although the red and blue light is more efficient, the broad spectrum achieved with the light engine in the picture can improve the culture for more photoreceptors.
When properly designed, this form of flexibility makes the lighting program with a very high CU very advantageous, and most of the light produced falls on the canopy of the plant without wasting it on the channel or the wall. This is essential for growers to choose gardening lighting systems.
Tips
Not all LED lighting systems are the same, so it is important for growers to obtain lighting design from the manufacturer, which will show the average PPFD at the specified installation height and the light distribution in the plant growth chamber mode. The shape factor and the light distribution of the horticultural lighting system will affect the number of fixtures required, which is another factor that affects the overall energy efficiency of the plant growth chamber.
The energy efficiency of gardening lighting systems depends on several factors, not just one factor. Using the correct measurement method to understand the factors that affect the energy efficiency of the horticultural lighting system will affect the overall profitability of the plant growth room.
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