1. Classification of Light Applications

Visual Applications: In lighting, the physical unit is primarily the luminous flux obtained by weighting the spectral radiant power with the visual function of an average human eye.

Non-Visual Applications: Utilized in animal, plant, medical, microbiological, identification, and data transmission applications, the physical unit is the radiant power or photon number.

2. Photon energy

LED luminescence is a phenomenon of energy conversion. When electrons and holes recombine, excess energy is emitted as photons. The shorter the wavelength, the higher the energy of the photon. Photons are the small units through which light transmits energy. Plants absorb these energetic photons during photosynthesis, which is driven by the energy packets of photons, not general light energy. This is why plants need photons to express photosynthesis.

Photosynthesis is a process generated by photon flux, where photons carrying energy are split by enzymes to produce new molecules from CO2 and H2O, but not all photons absorbed by plants produce the same level of photosynthesis. It is necessary to understand photosynthesis from an energy transfer perspective and view the relationship between photons and plants as a "light feast."

The number of photons in photosynthetic effective radiation is measured in two units: Photosynthetic Photon Flux (PPF), with a wavelength range from 400 to 700 nm, and the Yield Photon Flux (YPF), whose wavelength range can be determined based on the plant's photosynthetic response.

3. Parameters and Units of Plant Lights

Mole (mol)

In describing the fundamental units of matter such as molecules, ions, and photons, the mole is commonly used. A mole consists of 6.022EXP(23) fundamental particles of a substance, with the unit being the mole (mol). In the process of plant photosynthesis, the number of photons is also expressed in moles, with one mole of photons containing 6.022EXP(23) photons. Due to the large unit size in plant photosynthesis, many parameters are represented in micromoles.

1 mole (mol) = 1,000,000 micromoles (µmol).

One micromole (umol) contains 600 million billion photons.

PAR

Photosynthetic Active Radiation

Photosynthetically active radiation (PAR), referring to the specific wavelength range (400-700nm) used by plants for photosynthesis, is measured in two units:

Firstly, it is represented by photosynthetic radiation intensity (w/m2), mainly used in the general research of photosynthesis under sunlight.

Secondly, represented by the photosynthetic photon flux density (PPFD) in units of umol/m²s, it is primarily used for research on the effect of artificial lighting and sunlight on plant photosynthesis.

The method of using the photon flux density incident on the plant surface per second to indicate the radiative ability of the radiation source is known as the PPF_PAR method.

PAR accounts for approximately 50% of the total solar radiation. It is important to note that the unit of photosynthetic radiation does not reflect the impact of wavelength.

PPF

Photosynthetic Photon Flux refers to the number of micromoles of photons emitted per second by artificial light sources within the wavelength range of 400-700nm, measured in umol/s.

PPFD

Photosynthetic Photon Flux Density, corresponding to PPF, is the number of micromoles of light radiation emitted per square meter per second, measured in umol/m2s, which is a concept of density.

PPFD stands for Photosynthetic Photon Flux Density, representing the amount of PPF within a one-square-meter area.

PPFD is a physical quantity related to the distance from radiation, which is inversely proportional to the square of the distance from the source.

1PPFD stands for one photon per second per square meter.

1umol/m2s (PPFD) represents the number of photons in 10 square nanometers, with 6 photons present.

YPF

Generated Photon Flux

Refers to the number of photons per second emitted within the range of wavelengths produced by artificial light sources, measured in umol/s. The commonly recognized spectrum is 360-760nm, while for LED sources, the wavelength range is set at 380-800nm.

YPFD

Yield Photon Flux Density

The corresponding figure to YPF is the number of micromoles of radiation per square meter per second, measured in umol/m2s, which is a concept of density.

YPFD represents YPF within a one-square-meter range.

YPFD is a physical quantity related to the distance from radiation, which is inversely proportional to the square of the distance from the source.

YPFD provides a more precise expression of the light quantity of LED plant lighting.

For the red light blue spectrum, YPF = PPF; for other spectra, PPF.

The Difference Between PAR and PPFD: PAR is a physical concept, while PPFD refers to the unit of this physical concept.

The relationship between PPFD and PPF: PPFD is a basic quantity derived from cultivation process parameters, while PPF is a primary parameter in lighting manufacturing.

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

For the same PPF light source, the relationship between installation height and PPFD is that as the installation height increases, PPFD decreases at a rate of two times.

4. Quantitative Analysis Parameters Between Different Light Sources and Luminaires

For different artificial light sources, the following criteria can be used to compare their spectral performance parameters. These parameters can also be used to compare the spectral performance parameters of the same light source with different manufacturers under the same spectral shape. Typically, higher values are better, but larger numbers do not necessarily indicate higher plant growth efficiency; professional assessment with specialized skills is required.

PPF/w: Power Per Watt, representing the Power Per Fluorescent per watt.

PPFD/w: Represents the Photosynthetic Photon Flux Density per watt of electricity consumed.

YPF/w: Represents the YPF produced per watt of electricity consumed.

YPFD/w: Represents the YPFD per watt of electricity consumed.

These values are related to the spectral shape (light quality), and by dividing them by the price of plant lights, you can compare the price levels of different plant lights. The reliability of these values requires professional, third-party, independent analysis.

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