About The Mol, PAR, PPF And PPFD Of The LED Grow Light

1.Application classification of light

Applied to illumination, the physical unit is the main parameter that is obtained by weighting the spectral radiation power by the visual effect function of the average human eye.

Non-visual applications: applications in animal, plant, medical, microbiological, identification, data transfer, etc., physical units are radiant power or quantum number of light.

2. Photon energy

LED luminescence is a phenomenon of energy conversion. When electrons and holes recombine, excess energy will illuminate and produce photons. The shorter the wavelength, the higher the energy of photons. The photon is the smallest unit in the process of light transmission energy. It is this kind of photon with energy. Photosynthesis is driven by the photon energy packet instead of the general light energy. This is why plant photosynthesis requires photons to be expressed.

The energy ratio of a single photon at a wavelength of 400 nm to a wavelength of 700 nm is 1.75, that is, the blue light is 1.75 times larger than the red light energy.

Figure: At the same radiant power, the number of photons produced increases with increasing wavelength.

Photosynthesis is produced by photon flux. It is a process in which photons carrying energy decompose CO2 and H2O under the action of enzymes to produce new molecules. However, not all photons absorbed by plants produce the same photosynthesis, which requires energy transfer. Understanding photosynthesis from an angle, using light meals to understand the relationship between photons and plants

The number of photons of photosynthetically active radiation is measured in two units: photosynthetic photon flux (PPF) with wavelengths ranging from 400 to 700 nm, and secondly the resulting photon flux (YPF), which can be based on the photosynthetic response of the plant. Determine the wavelength range.

3. Parameters and Units of LED grow light


When describing the basic units of matter composition, such as molecules, ions, photons, etc., it is usually expressed in terms of molar amount, which is a basic amount of basic particles of 6.022EXP(23) substances, in mol (mol). The number of photons in plant photosynthesis is also expressed in terms of molar amount. A photon mole (mol) contains 6.022EXP(23) photons. Because of the large unit of mole in plant photosynthesis, many parameters are expressed in micromolar.

1 mole (mol) = 1000000 micromolar (umol).

1 micromolar (umol) contains 60 million photons.


Photosynthetic Active Radiation

The radiation used by plants for specific wavelength ranges (400-700 nm) for photosynthesis is called photosynthetically active radiation, and there are two types of labeling units:

One is expressed by photosynthetic irradiance (w/m2), which is mainly used for the

general study of photosynthesis of sunlight.

The second is the use of photosynthetic photon flux density PPFD (umol / m2s), mainly used for artificial light source and sunlight on plant photosynthesis research.

This method of measuring the photon flux radiated to the surface of the plant per second represents the radiation capability of the source, known as the PPF_PAR method.

PAR accounts for about 50% of the total solar radiation. It should be noted that the unit of photosynthetic irradiance does not reflect the wavelength.


Photosynthetic Photon Flux refers to the micromolar amount of photons emitted by an artificial light source per second in the wavelength range of 400-700nm, in units of umol/s.


Photosynthetic Photon Flux Density corresponds to PPF in the number of micromoles radiated per second per square meter of light source, in units of umol/m2s, which is the concept of density.

PPFD is a PPF that represents a range of square meters.

PPFD is a physical quantity related to the radiation distance and inversely proportional to the square of the illumination distance.

1 PPFD means that 1 micromoles per second of photons are radiated on a surface of 1 square meter.

How large is 1umol/m2s (PPFD), which means there are 6 photons in 10 square nanometers.


Yield Photon FluxRefers to the number of micromoles of photons emitted per second in the wavelength range emitted by the artificial light source, in umol/s. The commonly considered band is 360-760 nm, and for LED sources, the wavelength range is set at 380-800 nm.


Yield Photon Flux DensityCorresponding 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 representing 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 the light quantity of LED plant light.

For the red-light blue spectrum, YPF=PPF, and other spectra PPF<YPF.

The relationship between PPFD and PPF: PPFD is the basic amount derived from planting process parameters, and PPF is the main parameter for lamp manufacturing.

To understand the three concepts of radiation, lighting, and plant photosynthesis, we have produced the following table.

The difference between PAR and PPFD, PAR is a physical concept, and PPFD is the unit of this physical concept.

Comparison of the three concepts of radiation, illumination and plant photosynthesis of artificial light sources:






  Radiant energy (J)

  Light energy (LM.s)

Photosynthetic photon number (umol)


  Radiated power (W)

  Luminous flux (LM)

Photosynthetic Photon Flux (umol/s)


  Radiation intensity (W/sr)

  Brightness (cd)

Photosynthetic photon intensity(umol/s.sr)


  Radiation illumination(W/m2)

  Illuminance(Lx, Lux)

Photosynthetic Photon Flux Density(umol/m2/s)

The right side of the figure is the mounting height. As can be seen from the figure, proper installation height can reduce the power of the light source and reduce the system energy consumption.

For the light source of the same PPF, the relationship between the installation height and the PPFD is that the installation height is increased and the PPFD is decreased at the rate of 2 powers.

4.Quantitative analysis parameters between different light sources and lamps

For different artificial light sources, the following indicators can be used to compare the performance of spectral parameters between them. These parameters can also compare the performance of spectral parameters of different manufacturers under the same spectral form of the same light source. Generally, the larger the values, the better, but the values Big does not mean that planting efficiency is high and requires professional assessment with professional skills.

PPF/w: indicates the PPF generated per watt of power consumed.

PPFD/w: indicates the PPFD generated per watt of power consumed.

YPF/w: indicates the YPF generated per watt of power consumed.

YPFD/w: Indicates the YPFD generated per watt of power consumed.

These values are related to the spectral form (light quality). If you divide these values by the price of the plant lamp, you can compare the price of the plant lamp. The validity of these values needs to be reliable by independent third-party professional analysis.

Typically, agricultural sodium lamps are up to 2.2 umol/w, LED light sources, up to 2.1 umol/w.

5.Light quality, quantity and period

Light quality LQ

Light quality LQ (Light Quality) is a spectral form in a certain wavelength range, no unit.

Light quantity LI

Light Intensity (LI) is the number of photons that can be radiated by the light quality. It can be expressed in terms of photon flux or photon density, in units of PPF (YPF) or PPFD (YPFD).

Photoperiod PP

Photo Period PP (Photo Period), which is the sum of time in hours when the plant lights are turned on during a natural day.

6.The amount of radiation that plants need every day (important concept)

Many people are keen to study the compensation points and saturation points of plant radiation to estimate how large PPFD should be used in plant lights, from the compensation point to the saturation point range (as shown in the figure below), the amount of light in the selection of plant lights in this range has artificial The randomness, compensation point and saturation point are only qualitative analysis. The quantization process must consider other environmental factors and cannot be mechanically understood.

Usually, the compensation point and the saturation point appear only for a certain period of time, not constant. It is not scientific to set the PPFD with the compensation point and the saturation point. In our planting process expert system, we give the plant every square meter per day. The amount of radiation that is reasonably needed, this value is related to planting cost and planting quality. Our parameter is based on the planting process parameter DLI for long-term research in agricultural science, which has theoretical basis.


Daylight combination DLA

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. The unit is mol/m2d.

Since the amount of light of the plant lamp is constant under the photoperiod, DLA = 0.0036 * PPFD * PP. PP-photoperiod unit: hour.

DLA is the planting process parameter, and the PPFD required for plant planting in plant plants is calculated using DLA.

Disclaimer: The DLA parameters are defined by Xu Dong, a research institute for bright and solid light sources, and the references need to be noted.

Daylight integration amount DLI

Daily light integral (DLI): refers to the amount of photosynthesis per square meter per day of effective sunlight, in mol/m2d.

DLI is an important photosynthetic parameter in traditional planting. It is a technical parameter for long-term agricultural scientific research. It has universal planting guiding significance. Under sunlight, due to the photosynthetic irradiance of sunlight (converted into PPFD) with time and weather. In the ever-changing, this change will occur between the compensation point and the saturation point. Therefore, the DLI needs to be calculated according to the integral method. The preliminary calculation can be calculated by the average PPFD and the effective time (hours).

DLI calculated by the average method under sunlight, DLI = 0.0036 * PPFD (average) * effective time. Effective time unit: hour.

In outdoor planting, the DLI parameters will be affected by the saturation point. In the greenhouse, the indoor DLI is smaller than the outdoor DLI. The DLI of the greenhouse is usually smaller than the DLA. The DLA parameters are created, and the science provides whether the greenhouse is filled with light. The theoretical basis for the amount of fill light, the establishment of the DLA database of artificial light source, can provide the basic data system for plant plant application, which is of great significance, and hopes that agricultural researchers will participate in this work.

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, but it needs experimental data correction. The relationship between DLA and DLI is : DLA<DLI, such as lettuce with a DLI of 17, and a DLA of 9-11.

The above is the introduction of the spectral parameters of the plant lamp. It is very important to understand the parameters of the plant lamp. It is very important for the application and communication of the plant lamp. The standardized use of these parameters can correctly apply the plant lamp and research the plant lamp spectrum technology.

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