The development of technology is always accompanied by the improvement of efficiency. The artificial light source of facility agriculture is also the same. The quantum efficiency of LED lamp beads determines the performance advantages and popularity of LED plant lights.
Our research shows that planting follows the principle that light quantity determines the effect and light quality determines efficiency.
The quantum efficiency of light determines the amount of light and is the primary parameter of plant lights.
LED plant lights can replace other traditional plant lights based on the problem of light quantum efficiency.
The photon efficiency of the agricultural sodium lamp is between 1.6 and 2.2 μmol/J.
The source of the LED red-blue spectrum is between 1.4 and 2.6 μmol/J.
Plant lights are usually compared to light quantum efficiency, followed by light quality analysis.
The importance of photon quantum efficiency is mainly reflected in the following three aspects:
1. Affecting planting costs
Photon Flux of Plant Lamps PPF = Light Quantum Efficiency × Plant Light Power × Lamp Efficiency
Luminaire efficiency = photon efficiency of the luminaire / photon efficiency of the source
The luminaire efficiency is a constant and less than one after the secondary optical design of the luminaire.
Therefore, in order to obtain high photon flux, plant lamps can only increase the power of the lamps and select high-light quantum efficiency sources.
For example, the demand PPF = 1000 μmol / s, the luminaire efficiency is 0.75.
When the plant lamp QE=1.5μmol/J, the lamp power = 889W
When the plant lamp QE=2.1μmol/J, the lamp power=635W
The difference of 254W between the two is for the production of QE=1.5μmol/J, which is the heating power. In the summer when the power consumption is the largest, the higher air conditioning power consumption is needed to balance the temperature generated by this heating power.
At the same time, plant lights also need more cooling costs to ensure the use of plant lights.
Therefore, the light quantum efficiency will lead to product power consumption cost and temperature control cost, which directly increases the planting cost.
Usually we can reduce the power consumption of the plant lamp by secondary optical design and reducing the installation height of the lamp.
Our analysis shows that the parametric design of radiative heat transfer is generally not taken seriously.
The installation height of plant lights is limited by the physical radiation heat transfer. The current application cases do not provide the design parameters of radiation heat transfer. The planting of plant plants is generally high-light planting, and the radiation heat transfer problem affects the planting effect.
It is important to understand that high-gloss planting is not a solution to the planting process.
For LED plant lights, photon efficiency is the biggest factor affecting planting costs.
The “Specifications for the Quantum Efficiency Parameters of Plant Lamps”, which we have developed, proposes a minimum definition of photon quantum efficiency to prevent blind use of plant lights.
2. Plant lamp design requires photon efficiency
Most of the plant lamp designs are based on the number of lamp beads. This design method is also the reason for the continuous modification of the design scheme. The design cycle is long and the parameters are unstable.
Regarding the difference between the lamp-to-bead ratio and the radiation ratio, we can pay attention to our future articles.
At present, most packaging companies do not provide complete photometric efficiency specifications for lamp beads.
The main reason is that the spectral parameter measuring equipment has large repeat error and algorithm problems.
Before using the quantum efficiency of light to design a plant lamp, it is necessary to ensure that the optical quantum efficiency value error of the lamp bead is within the allowable range.
Cases of designing plant lights using light quantum efficiency:
Design requirements: Light quality: 450nm+660nm, 2835 package, radiation ratio R:B=3:1, PPFD=80μmol/m2s under the lamp, the Lange-type light distribution, the lamp efficiency is 0.8, the installation height is 0.4m.
Our institute tests the quantum efficiency parameters of a company’s lamp bead:
QE (660) = 2.43 μmol/J.
Calculated according to the formula:
According to the red and blue radiation ratio:
Red light PPF=51.2×0.75=38.4μmol/s
Blue light PPF = 51.2 x 0.25 = 12.8 μmol / s.
The power consumption of 450 nm = 12.8 / QE (450) = 7.94 W.
The power consumption of 660 nm = 38.4 / QE (660) = 15.8W.
Total power of the light source P=7.94+15.8=23.74W
Assume that the drive power efficiency = 0.85
Total lamp power = 23.74/0.85 = 27.93W
The photon efficiency value of the plant lamp=51.2/27.93=1.833μmol/J
The number of red and blue lamp beads is calculated according to the drive current and the respective Vf of the lamp bead (omitted)
As can be seen from the above design case:
1) The lamp QE value determines the lamp power.
2) The error of the QE value affects the design result.
3) The QE value without the lamp bead is not able to accurately design the plant lamp.
4) This method can make a preliminary quotation according to customer requirements.
When this radiation is better than the QE of the light quality, it is convenient to design plant lights of other power levels.
For example: This light quality application in the greenhouse fill light, requires the lamp PPF to reach 1200μmol / s, how much power plant light is needed?
Since QE=1.833μmol/J is known, the power of the lamp=1200/1.833=654.66W
It can be seen from the above design case that the plant lamp design is actually a complete parameter calculation process. If the optical quantum efficiency error is small, the design calculation result can be directly applied to the plant lamp manufacturing, which greatly reduces the product development cost and cycle.
For lamp beads that do not provide photon efficiency, the design should be carefully selected.
Tip: The packaging factory needs to provide the photon efficiency of the lamp bead, and the plant lamp manufacturer also needs to provide the photon efficiency of the lamp.
3. Affect the life of plant lights
The annual working time of plant lights is between 5200-5700 hours. The attenuation of light quantity will affect the planting effect. It needs to be considered in the design of plant lights. This attenuation is proposed by the planting process.
The attenuation of the amount of light in a plant lamp is actually a decrease in the efficiency of the photon.
The light amount attenuation is mainly determined by the operating temperature of the chip, and the improvement of the light quantum efficiency is mainly to reduce the heating power of the chip.
The quantum efficiency of light has a great influence on the service life of plant lamps, and both plant lamp manufacturers and users need to pay attention to this problem.
The plant lamp is a parametric product. The application needs to analyze the planting data according to the precise parameters of the plant lamp. The spectral parameters of the plant lamp are only guaranteed to be accurate, and the planting process will show the effect.