Basic Knowledge of LED Grow Lighting

What is light?
Light is an electromagnetic wave. This wave contains a wavelength which will be measured in meters, nanometers to be precise. Mathematically speaking that’s 0.000000001. this can be abbreviated by exploitation nm. White light could be a mixture of all wavelengths of light. The hue or color that a light provides off is owing to the number of light from a curtain wavelength. Below 400nm is termed ultra-violet or ultraviolet illumination. on top of 700nm is infrared or IR lighting. The wavelength of every color is as follows: (note that as colours meet up with to every alternative the hues mix together)
  • UV C: 100-280nm
  • UV B: 280-315nm
  • UV A: 315-400nm
  • Violet: 380-450nm
  • Blue: 450-495nm
  • Green: 495-570nm
  • Yellow: 570-590nm
  • Orange: 590-620nm
  • Red: 620-750nm
  • IR A: 700-1400nm (near infrared)
  • IR B: 1400-3000nm (mid infrared)
  • IR C: 3000nm-1mm (far infrared)
The human eye sees light from ~400nm to ~700nm. There are an oversized variety of measurements utilized in lighting and optics. i’m progressing to cowl the common ones during this thread. If you’d prefer to see a lot of click here.


This is directly from Wikipedia, as they explain it all right.
“ The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total “amount” of visible light emitted by a supply. radiant flux differs from power (radiant flux) in this luminous flux measurements mirror the variable sensitivity of the human eye to totally different wavelengths of sunshine, whereas flux measurements indicate the whole power of all light emitted, freelance of the eye’s ability to understand it. A lux is one lumen per square meter. “
Lumens area unit skew toward what the human eye sees higher. Therefore, lights that contain a high amount of greens and yellows have the next worth given to them than those that contain less or no green and yellow. this can be an okay measure to use once comparing two bulbs/panels of the precise same lighting sort or wavelengths, however terribly poor once comparison light sources of various varieties. For example: once comparison 2 HPS bulbs (with roughly identical spectral output) the one with the upper lumens are going to be a brighter bulb. However, if you’re making an attempt to match two CFL bulbs one that’s cool white and one that’s heat white, the nice and cozy white can have roughly five a lot of lumens per watt.
Photosynthetically active radiation
Photosynthetically active radiation or PAR could be a measurement of all light between 400 and 700nm. this can be wavelengths of light that management MOST chemical process. in contrast to lumens, PAR doesn’t skew the results of the photon count toward any given color and is expressed in µmol photons/ m2/second. It merely records the amount of photons of the wavelength(s) being measured. you’ll additionally see the term PPFD or photosynthetic photon flux density expressed as W/m2. this can be the measure that’s most valuableeful|most respected|Most worthy} to us as plant growers.
Radiant Flux
“Radiant flux or radiant power is that the measure of the total power of electromagnetic radiation (including infrared, ultraviolet, and visible light). the ability could also be the whole emitted from a supply, or the whole landing on a selected surface.” Again, Wikipedia contains a nice definition. this can be largely utilized in technical publications and development, however is that the most correct measure which will tend. it might be nice to use this measure for growing but you’re unlikely to examine it on any packaging.
Chlorophyll and light absorption.
Chlorophyll is that the main a part of photosynthesis. this can be why leaves area unit green once light by white light. chlorophyll could be a inexperienced pigment that is found all told plants. However, there’s quite one sort of chlorophyll. There area unit a minimum of six well-known varieties of chlorophyll and possibly a lot of (the last chlorophyll to be discovered was in 2010). We tend to all recognize that chlorophyl is what makes plants grow and that they absorb the sun/light to create that happen. many of us aren’t awake to all of the opposite photoreceptors (light catchers) in plants. There area unit between two hundred and 300 photoreceptors in each plant. Some botanists believe that there area unit still a whole lot if not thousands to be discovered. These antenna or accent pigments play a far larger role than most of the people assume. The reactions that occur inside a plant area unit terribly complicated. light hits the leaf, excites a photoreceptor pigment that then performs a chemical reaction that’s passed on to subsequent. As PS1 loses and negatron it gains one from PS2, this can be referred to as hill reaction. This method happens in chlorophyll, move through carotenoid, zeaxanthin, carotene, lycopene, and so to chlorophyll. this can be only for the assembly of sugars that the plant uses to grow. after we quote cannabis or alternative higher plants there area unit variety of alternative reactions that occur for the building of cannabinoids and alternative compounds used inside the plant. Below area unit a number of the wavelengths for plant photoreceptors. (Note that almost all photoreceptors have multiple peak absorption points.)
  • Chlorophyll A: 430, 662
  • Chlorophyll B: 453, 642
  • Alpha Carotene: 442, 444, 478
  • Beta Carotene: 425, 480
  • Zeaxanthin: 423, 451, 483
  • Lutein: 420, 447, 477
If you compare that list with the above list of wavelengths, you may see that none of those photoreceptors are in the green or yellow region. this can be another example of however the lumen measure doesn’t equate to the expansion of plants. Or find more knowledge of Spectrum
Emerson Impact
This leads ME to the Emerson impact or Emerson enhancement effect. This has been utilized in virtually every plant photoreceptor study since he revealed his 1st paper on that in 1957. once illuminating plants with 700nm wavelength red light, he noticed  that photosynthesis was slowed greatly. identical occurred once light with 650nm red light solely. However, the mix of the 2 generated a dependent response and increased  the expansion rate to double that of the only sources combined (a fourfold over every light alone). His later work indicated that there wasn’t one however 2 photosynthesis traps. we tend to currently decision these PS1 and PS2, wherever every system transfers energy and electrons to every other increasing productivity.
comparison of action spectrum and absorption spectrum

Horticultrue Lighting Parameters

In a previous article, the role of LED illumination in green-house environments for growth of crops were mentioned. the flexibility to color mix numerous LED sources to match the photosynthetic absorption curve of various crops and conjointly alter levels for every wavelength for max productivity, are huge benefits that LED lighting will offer for horticultural lighting applications.

In this article, many vital parameters that require to be measured to encourage the expansion and productivity of crops are mentioned. Measuring these parameters and monitoring them on each day basis, is that the key to promoting extremely efficient plant growth.

Before examining totally different observation parameters for horticulture lighting, the “Action Spectrum” has to be represented. it’s vital to not confuse the spectrum with spectrum of a plant as there’s a big distinction between the 2.

Plants absorb radiation largely within the 400-700 nm visible vary and convert greenhouse gas uptake and water into element and aldohexose. the number of absorption in every wavelength depends on the cellular structure of the plant and will dissent from species to species somewhat, but it stays largely within the visible range. spectrum describes the wavelengths that are most vital to photosynthesis and drive its processes. Figure 1, shows a typical plot of absorption and action spectra and therefore the comparison between them.

comparison of action spectrum and absorption spectrum

As observed in the figure, the plants have high absorption within the red and blue wavelengths and smaller absorption in inexperienced wavelengths. This explains the inexperienced color of most plants since a high share of the inexperienced wavelegth in daylight is mirrored off the plants. there’s a similarity in form between the spectrum and therefore the spectrum. This spectrum thought was been pioneered by KJ Mcree within the 70’s who studied the spectrum or Photosynthetic Active Radiation (PAR) for a range of plants.

Another parameter of importance is that the ratio element molecules emitted by plants, P, to variety of incident Photons ia. This defines the quantum yield of photosynthesis &Phi.

In 1922, Otto Warberg and E.Negelein (Reference) examined this method and came up with the magnitude relation of four to one, implying that a minimum of four photons ar required to unleash one molecule of element. This was the accepted theory for pretty much twenty years. Later experimentation with improved and totally different techniques by Emerson and Daniels showed this magnitude relation to be 8:1. The first reason this magnitude relation differed from Warberg’s hypothesis was the wrong assumption that ΔO2=-ΔCO2 or in different words absorption of greenhouse gas is adequate to emission of element molecules. different researchers have on an individual basis measured the 2 parameters that made additional correct results. subsequent experiments specializing in radioactive co2 intake confirmed the 8:1 ratio.

photosynthetic quantum
The other vital parameters for horticulture lighting are: Spectrum, PPFD, YPFD, DLI, Intensity in lux, Red/Blue, Red/Far Red. A instrument which might quantify each of these parameters is extremely useful for horticultural lighting applications and green-house crop growers. However, one should understand the usefulness of measuring these parameters first.

Spectrum: For artificial lighting it’s vital to understand the spectrum. whereas employing a mixture of LED’s, one will select a mix of wavelengths that ar most vital to the {photosynthetic|photosynthetic |chemical method|chemical change|chemical action} process and drive it additional expeditiously. For a broad-band light like high pressure sodium (HPS), one has to recognize the number of photosynthetic Active Radiation (PAR) within the spectrum of the lamp. selecting the right wavelengths mixtures with LED’s, it’s potential to provide healthier plants with thicker leaves and exaggerated branching and flowering.

PPFD: photosynthetic gauge boson flux takes into consideration the actual fact that red light is doubly as effective as blue light per incident watt. this is often as a result of the actual fact that the amount of photons per unit of energy is proportional to wavelength. thus larger wavelengths like red, carry additional photons as compared to blue wavelengths that carry less. For this reason, in agriculture it’s common apply to use PPFD in units of mol/m2/s (1 mol=6.023×1023 photons) rather than energy units. Since the amount of gauge bosons for every wavelength is additional vital that the particular energy of the photon, PPFD could be a additional appropriate unit to live the sunshine intensity in quantum units once promoting photosynthesis. This unit conversion assumes that every gauge boson of sunshine equally contributes to the photosynthesis process and doesn’t take into consideration the quantum yield.

YPFD: A additional correct estimate of photosynthetic activity are often obtained if the quantum yield plot is taken into consideration as a coefficient issue. Not every gauge boson equally contributes to photosynthetic activity. Therefore, if the precise response of the plant is taken into account, then a additional correct estimate of the photosynthetic activity is obtained that is named Yield photosynthetic flux and is additionally measured in units of mol/m2/s. this could even be known as Weighted Spectrum.

DLI: Another vital parameter is Daily light Integral that is outlined because the total variety of photons natural event per square metre in in the future. DLI is measured in units of mol/m2/d and every plant contains a specific demand of DLI for its growth. Values travel between 6-18 mol/m2/d ar common betting on the actual plant. there’s a relationship between PPFD and DLI that is given by:

DLI=PPFD x light hours per day x (3600/1000,000).

One will see from this formula that there’s a trade-off between PPFD and variety of sunshine hours needed to attain a particular DLI price. If there’s a particular quantity of natural lighting on the market for a green-house, it’s to be deducted from the initial DLI price for correct artificial fixture calculations. Taking into consideration the DLI, PPFD and variety of sunshine hours per day, one calculate the full variety of fixtures needed in an exceedingly green-house to illuminate the crops

Light intensity in lux or Foot-candles: In low lightweight levels the method of respiration is dominant and plants consume element. the method of respiration is freelance of sunshine intensity and thence the plot of Reaction Rate of Respiration vs. intensity is flat. As intensity will increase from darkness and chemical action begins, there’s additional production of element and at a specific intensity level, the number of element consumed by respiration becomes adequate to the number of element made by photo-synthesis. this is often known as the compensation purpose and past now wherever the number of element made, exceeds the number of element consumed, the plant will raise its reserves, grow and reproduce. Not all plants have a similar compensation purpose and a few reach now at higher intensities than others. usually crop plants like soybean and corn, reach the compensation purpose at higher intensities. Figure five below shows the compensation purpose thought.

Compensation point, respiration and photosynthesis

R/FR and R/B: many studies by horticulture scientists have examined the magnitude relation of R/FR and R/B and its result on the expansion and productivity of plants. for instance studies have shown that low blue light from heat white LEDs cause exaggerated stem elongation and leaf enlargement. On the opposite hand, high blue light from cool white LEDs has resulted in additional compact plants. normally the presence of blue light has important effects on morphology of plants other than Photo-synthesis. The R/FR stimulates physiological processes like flowering, setting winter buds and vegetative growth.

Unique meter that may live several parameters: within the past Botanists and greenhouse growers had to use four totally different meters to live

  • the spectrum of sunshine shining on their crops,
  • the number of chemical process Active Spectrum
  • the intensity in lx or Foot-candles and
  • R/FR ratios.

This method has been terribly tedious and therefore the knowledge needs to be transferred on an individual basis to desktop computers to perform the analysis.