At present, many countries generally use the optical quantum unit expression for the spectral parameters of plant lights. From the application point of view, the use of optical quantum units to express spectral parameters is more scientific, and also contributes to the study of plant photosynthesis, and is also conducive to the calculation of other environmental control quantities such as CO2. With regard to control, the study of light quality has evolved from simple photosynthesis to photomorphogenesis. For the FR part, the light quality needs to be designed in the plant lamp spectrum, but the PPF_PAR method cannot describe the role of Fr. Therefore, The PPFD description has limitations and requires a YPFD description.
With the deep research on the absorption spectrum of plants, the spectral design of LED grow light began to turn to the matching design of light quality and light quantity based on planting environment. The purpose is not only to meet the photosynthesis needed for plant growth, but also to increase the plant quality. The improvement of quality, the realization of plant taste and nutritional balance will become the direction of future plant lamp spectrum design.
YPF and YPFD
With the deepening of research on plant physiology, the wavelength domain of PAR has its limitations. For LED light sources, this limitation is particularly prominent, so YPF and YPFD parameters are introduced.
The resulting photon flux YPF (Yield Photon Flux) refers to the number of micromoles of photons radiated per second in a range of wavelengths emitted by the artificial light source, in units of umol/s. The wavelength band is generally considered to be 360-760nm, and for LED light sources, the wavelength range is set to 380-800nm.
The difference between YPF and PPF is that the wavelength range of YPF is larger.
YPFD（Yield Photon Flux Density）
Corresponding to YPF is the number of micromoles per square meter of radiation per second, in units of umol/m2s, which is the concept of density.
YPFD is YPF in a range of one square meter.
YPFD is a physical quantity related to the radiation distance, which is inversely proportional to the square of the distance of illumination.
YPFD can more accurately express LED grow light’s light quality and light quantity.
For a monochrome 430-660nm LED source, YPF = PPF, other spectra PPF ≤ YPF.
For the YPFD concept, the current paper has three views. One is that YPFD only represents the photosynthetic photon flux density in its wavelength domain, and the other is photosynthetic correction by plant relative quantum efficiency curve (RQE) in its wavelength domain. Another point of view is that YPFD indicates the photon flux absorbed by plants.
Obviously, the third viewpoint is wrong. If we know in advance how many photons are absorbed, the research on luminescence of plant lamps is almost perfect, and now the situation is that we do not know the optimal photosynthetic spectrum and the weight of the absorption band; The basic concept of YPFD and PPFD is the preset value of the planting process, which is the guaranteed amount of optical radiant energy.
The second view has the following problems:
1) RQE has limitations. Mokley’s RQE is based on plant leaf research rather than the overall study of plant canopy.
2) RQE does not form the standards adopted by countries.
3) There is also controversy in the academic weighting of plant photosynthetic efficiency in the blue or red wavelength.
4) The actual application effect of the spectrum after RQE weighting is not obvious.
5) The RQE curve is still being studied or will be replaced by a new plant photosynthetic efficiency curve.
6) The LED light source parameters corrected by RQE are prone to confusion in the data evaluation of each research topic.
7) PAR has limitations on the expressions of 365-400nm and 700-780nm, and it is necessary to have a dimension (YPFD) that can cover these bands.
Therefore, we believe that the YPFD parameter is a photon flux density that can produce photosynthesis over a wider band.
Photon energy efficiency QE
The artificial light source is in the wavelength range of 400-700nm, and the efficiency of converting unit electric energy into photon is represented by PPF/W. The photon energy efficiency QE expresses the conversion ability of the light source to the photon.
Photon energy efficiency calculation formula: QE=PPF/W Unit: umol/J, (W: power consumption of light source).
QE is a parameter related to the spectral shape. The higher the value of this parameter, the larger the PPFD value. When the same PPFD value indicates that the artificial light source is more energy-efficient, the QE value has a problem that the green light content is large and the efficiency is distorted. For the LED light source, the best is based on comparisons under the same light quality.
The QE parameter is the original parameter of the spectral design, QE is the parameter related to the spectral measurement technology, the spectral parameter measurement is not accurate, the QE value is distorted, and the QE value distortion causes a very large error in the spectral design result.
Now, the QE of agricultural sodium lamps is up to 2.2, and the QE of LED light sources is up to 2.1.
LED lamp beads, LED grow lights, and other light source plant lights, QE must be marked, and need to be marked with the light quality.
Daily light amount (DLA)
In the question of led grow lights, the most frequently asked question is what the spectrum ? How many PPFD?
If the planting variety and environmental conditions are not provided, in fact, this problem cannot be accurately answered. Plant planting is the conversion process of light radiant energy. The light radiant energy follows the law of conservation of energy in this conversion process. For a certain variety of plants, the first thing to be determined is the light radiation energy that plants need every day, otherwise, there is no basis for the calculation of a series of parameters.
Daily light amount (DLA) refers to the number of moles of photons generated per square meter of PPFD per day during the photoperiod of the artificial light source, in mol/m2d.
Since the light quantity of the plant lamp is constant under the photoperiod, the calculation formula of DLA:
DLA = 0.0036 * PPFD * PP. PP-photoperiod (hour)
DLA is calculated based on the combination of plant varieties and planting environment, and the DLA of different plants is different.
DLA is the main parameter of planting plant and greenhouse light-filling planting process. It is the main basis for plant lamp design. DLA can be obtained through experimental data or weighted by DLI, and needs experimental data correction. In our planting process expert system, we give the radiant energy DLA that is reasonably required per plant per square meter per day. This amount is related to planting cost and planting quality. The DLA parameter is based on the DLI parameter of agricultural scientific research sunlight, it has developed on the basis of theory.