Knowledge Base

• People eat energy through their food (calories) and grow. Plants can use the energy of solar radiation for growing through photosynthesis
• In photosynthesis, energy-poor molecules are transformed into high-energy molecules by the energy of light
• CO2 is used and oxygen is generated

en.wikipedia.org/wiki/Photosynthesis

Photoactive pigments are molecules, which which certain probability can perform certain actions when absorbing light of a certain wavelength. Example: Various chlorophylls, carotenoids, phytochromes [Links].

Plant secondary metabolism is very important to plants and some can contribute to photosynthesis and other metabolic processes in the plant. Unlike chlorophylls, however, secondary metabolites are not vital to the plant. They are available in electron transport chains in various processes important for homeostasis in plant growth. Carotenoids make plants stronger against pests. E.g.: carotenoids, phytochromes, xenophylls

en.wikipedia.org/wiki/Plant_secondary_metabolism

• Chlorophylls are color pigments that give plants their green color which, after receiving electromagnetic radiation of a particular wavelength, can to a certain probability produce energy for plant growth. Chlorophylls are the most important source of energy for plants and vital for plants.
• There are several different chlorophylls and bacteriophyllophylls, which are slightly different. Chlorophyll a and b are particularly relevant for plant growth.
• The absorption spectra of Cholophyll a and b are shown here:

Spectrum: upload.wikimedia.org/wikipedia/commons/b/bb/Chlorophyll_spectrum.png

en.wikipedia.org/wiki/Chlorophyll

Cryptochromes are heavy flavoproteins that can absorb blue light. Flavoproteins are fundamental to all processes of cellular respiration, as they are involved in the corresponding electron transport chains.

Xanthophylls occur in the plasticides of all photosynthetic active cells of plants. As pigments in the cell membrane they protect against photo-oxidation of cell components.

Flavonoids are a group of phytochemicals, which include a large part of the floral colorants. They fulfill a multitude of important functions in plant growth.

en.wikipedia.org/wiki/Flavonoid

Carotenoids have a different action spectrum compared to chlorophylls. The metabolic process can contribute energy to photosynthesis, but also to changes in the plant that are very important for pest resistance.

en.wikipedia.org/wiki/Carotenoid

Keto carotenoids are a group of carotenoids that has important functions in plant growth and possesses a different absorption spectrum than the other carotenoids.[Spectrum]

• 1 µmol of radiation means about 60,220,000,000,000,000 individual photons with wavelengths of the light spectrum of a lamp. A single sol lamp emits about 150 ,mol per second. 12 hours are 43,200 seconds - it's easy to imagine how complex plant growth is.
• Every single photon can be absorbed with certain probability in one of the myriad molecules of the plant, it should hit the plant and trigger a certain metabolic process
• The countless number of metabolic processes results statistically in an energetic homeostasis, which determines the quality of plant growth.

The R: FR ratio refers to the red ("red") to the deep red ("far red") ratio of a light spectrum. It has a big impact on the photomorphogenesis [LINK] of a plant. According to Smith et al. it was defined in 1982 on the wavelength ratio (650-670nm) to (720-740nm).

• Radiation outside of the PAR, here over 700nm contributes to the metabolic processes in the plant. The phytochrome system is important for detecting the daylength of plants. By controlling the ratio between 660nm and 730nm, the growth of a plant can be influenced.
• If too little 730nm radiation is present, the metabolic processes of the plants can come in an "energetic congestion", which limits the plant growth per watt (energy).
• The phytochrome system consists of two molecules, which under irradiation with 680nm (P) in the form Pr passes. If the form Pr is irradiated with 730 nm radiation, the reversible process is reversed.
• The plant "senses" the R: FR ratio and thus the time of day by the phytochrome ratio Pr: Pfr.
• The R: FR ratio changes during the day: At early dawn and in the sunset, the ratio R: FR is less than 1, while it is significantly less than 1 during the day.
• With the help of the phytochrome system, the growth of plants can be influenced morphologically and qualitatively with spectral impulses.

[Spectra Pr and Pfr]

• The light saturation point describes the light intensity at which the oxygen production of a plant and thus the rate of photosynthesis flatten. 
• Even more light has no effect on the rate of photosynthesis unless you artificially add CO2 that the plant can work with.

• Watt is the basic physical energy unit. The energy of a photon can be calculated by the wavelength of the photon, the speed of light at which the photon travels, and a constant value (Planck's constant).
• The energy of a photon decreases in proportion to the wavelength. A red photon with 660nm has 50% less energy than a blue photon with 440nm.
• µmol is an indication of the number of photons of a lamp. 1 µmol is about 60,220,000,000,000,000 single photons, but that does not say anything about how much energy each photon has.

Energy conservation applies: A photon is either absorbed, reflected or transmitted on a medium (molecule). Each of these three events happens with a certain probability between 0-100%, in the sum total of 100%.

A+R +T = 100%

• The color temperature is white light color, which most closely corresponds to the spectral ratio of the radiation of a blackbody. It is measured in Kelvin [K], the temperature of the correlating blackbody.
• The sun has a temperature of about 5700K
• The light spectrum of the sun fluctuates during the day on Earth between 2500-12000K, depending on the time of day or sun position.

• PAR (photosynthetically active radiation) is by definition electromagnetic radiation with wavelength between 400-700nm.
• The PAR value has only limited validity: Green radiation around 550nm is not as efficiently absorbed by a plant as red or blue radiation.
• The PAR value contains neither UV radiation nor deep red radiation with 730nm, which are important for plant growth.
• The PPFD is the photon flux density in these areas and is measured in µmol / m²s, ie in photons per square meter per second.
• The PBAR is the "photobiologically active radiation" and extends the PAR of 280-800nm wavelength. It takes into account important UV, FR and IR radiation.

The Yield Photon Flux (YPF) is a bit more advanced than the PAR value because it is multiplied by the action spectrum of plants and is not simply weighted in the range 400-700nm. However, this value is not universally meaningful.

• The "light spectrum" refers to the energy spectrum in intensity per wavelength.
• Caution: Intensity can mean either the energy per wavelength or the number of photons per wavelength.
• There is a reflection, absorption, transmission, and emission spectrum

• Lumens & Lux are used to quantify the brightness to the human eye
• Incidentally, the lux and lumen units are sometimes used to describe a plant growth light
• Lux and lumens are energetic light units, which are calculated with the absorption spectrum of the human eye, which has nothing to do with plants

• The Color Rendering Index, or CRI, is a value for the color rendering of a light source in relation to the light spectrum of an ideal blackbody to which we humans have become accustomed because it is similar to that of the solar spectrum.

• For plants the CRI has no meaning.

• What efficiency means must first be defined. Ultimately, there are several factors that contribute to the overall quality of a product.

• Electro-Optical Efficiency: The conversion of electrical energy to electromagnetic radiation has an efficiency between 0-100%. Typically, one NDL has 25%, one LED about 40% (strongly manufacturing temperature and material dependent)
• Sustainable efficiency: The radiation decreases with lifetime. At lower temperatures, LEDs age more slowly than at high temperatures.
• PAR / W or µmol / J is the number of photons (400-700nm) emitted per electrical energy. This value decreases with aging of the lamp and says little about the quality of a luminaire.

The light bulb still knows everyone today. Fluorescent tubes, sodium vapor lamps and energy-saving lamps have dominated the market in the lighting industry in recent decades. LED technology has completely changed and modernized the lighting market, enabling efficient light with any color of light.

• Current flow in doped semiconductors excites electrons to a higher but unstable energy level. When the electrons fall back down to the initial level, the energy is emitted in the form of light.
• The light color of the LEDs is determined by the doping and the material of the semiconductor. The width (half width) of the spectrum of an LED normally varies by about 30nm.
• White LEDs are usually realized with blue LEDs that shine through a phosphor and partially excite it. Then broadband (about 200nm bandwidth) radiation of low energy is emitted. The blue radiation of the LEDs and the green-red radiation of the phosphor add up to a white light. In the meantime, there are also red phosphors in the plant lighting segment that do not emit green radiation.

• By applying a voltage, particles are excited in a gas mixture, which emit light. The efficiency of high-pressure gas discharge lamps is max. approx. 25% (Cf. LED approx. 40-45%)
• The light spectrum is determined by the gas mixture and can not be determined as easily as with LEDs.
• As a result, the efficiency of the gas discharge lamps (yield per watt) is significantly lower than with LEDs.