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Lighting

 

~A Cultural Healing and Life Compilation and Writing.

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Emoticons are safe bonus links, most youtube, click them.

  1. Advanced Section I - Understanding light, photosynthesis and how to select grow lighting
  2. Advanced Section II - Lighting & Reflector Section
  3. Advanced Section III - Plant Growth and Light
  4. Advanced Section IIII - Understanding Light Measurements
  5. Advanced Section IV - Advanced Lighting Information and formulas.
  6. Indoor Garden Environment

 

Section IV

Advanced Lighting Information and formulas.

 

:office-chair-smiley-emoticon:

 

When a more accurate estimate of the photosynthetic activity is needed, the exact response curve of the plant may be considered, leading to the yield photon flux density (YPFD). In the following examples, only PPFD will be used, although YPFD may be used instead in exactly the same way if necessary.

  • Also, the term PAR (or Photosynthetically Active Radiation) is used instead of PPFD by some practitioners; however, PPFD is the term recommended by the CIE (The International Commission on Illumination). In some research papers, the acronym PPF (Photosynthetic Photon Flux) is used interchangeably with PPFD.
  • Strictly speaking, it implies an integrated value of the PPFD over a given area.
    • If that area is completely surrounding the light source, PPF is analogous to the luminous flux used in general lighting, whereas PPFD is analogous to the luminous flux density or Illuminance used there.

It is very important not to use general lighting units such as lumens, lux and foot candles in horticultural lighting directly since they are all tied to human vision instead of photosynthetic action.

  • However, it is possible to calculate the coefficients for converting these units into PPFD values, if the corresponding spectra are known. Those have to be used sometimes in the absence of quantum meter data but are spectrum-dependent, so they are generally not transferable between different spectra.
    • For example, the conversion coefficient between the lux values (such as obtained with a photographer’s light meter) and PPFD (in mmol/m2s) is 0.018 for sunlight, 0.012 for high-pressure sodium light, 0.014 for metal halide light, etc.
      • It should be noted that the analogous conversion coefficients for LED light sources may reach and exceed 0.100, especially if the latter have little or no emission around 555 nm – due to the sensitivity maximum of the human eye being at that particular wavelength.
      • All of this underscores how unsuitable general lighting metrics are for horticulture applications.

 

Daily Light Integral (DLI), horticulture lighting

This is the total number of photons falling per square meter of area in a day, expressed in moles. Each plant has a certain DLI requirement in order to develop, and these values are known for a range of plants.

This is another manifestation of the fact that photosynthetic action is proportional to the total number of photons absorbed by the plant.

  • DLI values of 10-12 mol/m2.d have been found to be sufficient for most shade-intolerant plants.
  • Plants requiring full sun may need higher DLI values (18 mol/m2.d or even more), and those requiring full shade – lower ones (6 mol/m2.d or even less).
    • Assuming a constant PPFD level (common in artificial lighting), it is related to DLI as follows:
      • DLI = PPFD x number of hours of light on per day x 0.0036,
        • where the unit conversion factor of 0.0036 is the number of seconds in an hour divided by a million. The number of hours must be converted to decimal format to be used in this formula (for example, 11 h 6 min 40 s becomes 11.1111 h).

By rearranging the last formula, one can calculate either the necessary PPFD value to reach a given DLI target over a given number of hours, or the necessary number of hours that lighting with a given PPFD value needs to be on per day, in order to achieve a certain DLI target.

  • For example, a DLI of 12 mol/m2d may be achieved by using 200 µmol/m2s of light over 16 h and 40 min, 250 µmol/m2s of light over 13 h and 20 min, 300 µmol/m2s of light over 11 h, 6 min and 40 s, etc.
    • If any part of the DLI is provided by natural light, it must be subtracted from the original target DLI value for proper artificial lighting calculations.
    • Outdoor DLI levels vary with season and latitude, and average monthly values by region are available for the contiguous US.
      • It must also be kept in mind that about half of the outdoor daylight is typically lost by the time it enters a greenhouse, due to absorption by its structure.

From the above calculations, it is obvious that there is a trade off relationship between the PPFD value and the number of light hours required to reach a given DLI target. Since the cost of horticulture lighting is directly proportional to PPFD, a good strategy is to use its lowest value at the corresponding longest light hours the plants can tolerate.

(Many plants require a daily period of darkness, which will be discussed separately.) A calculation of the required number of horticulture fixtures can be done from the average PPFD value needed as follows:

Number of Fixtures = (PPFD Target x Total Plant Canopy Area)/(PPF per Fixture x CU)

  • In this formula, PPFD must be in µmol/m2s,
  • the plant canopy area must be in m2,
  • the PPF per fixture – in µmol/s and CU is the coefficient of utilization,
    • which is a dimensionless fraction. PPF per fixture is the horticulture analog of the fixture lumens in general lighting, and can be calculated from the former using the same coefficients as for the calculation of PPFD from lx values mentioned earlier.
    • For other spectra (such as LED fixtures), the PPF value may be obtained from the manufacturer.
    • CU represents the fraction of the light generated by the fixtures that is falling on the task surface.
      • For example, if 75% of that light is reaching the task surface and the other 25% isn’t, CU=0.75.
        • CU depends on the geometry of both the light source and the entire setup,
          • can be calculated accurately, for instance by using freely available software such as Dialux.
          • It can be as low as 0.50 or as high as 0.90, and will generally increase with the area, all other factors being the same.
          • If CU is unknown, the value of 0.70 can be used as a starting estimate.

For example, the total number of fixtures, each emitting 50 mmol/s, needed to provide an area of 20 m2 with 200 mmol/m2s at a CU of 0.77 will be (200 x 20)/(50 x 0.75) = 107 (any fractional answers have to be rounded up in order to reach the PPFD target).

  • Another consideration is the uniformity of the light produced by the fixtures. It should be maximized by spreading the fixtures out as evenly as possible over the task area, taking into account the light distribution pattern of each fixture.
  • This can be done at the lighting design stage,
    • Also verified at the implementation stage, e.g. with a hand-held PPFD meter.

In summary, the total number of horticulture light fixtures needed for a given project can be calculated from the average PPFD target, which in turn can be calculated from the DLI target for the plants at any fixed light hours value. There are some important additional considerations regarding the latter value, as well as the proper spectral composition of the light.

 

Purdue University DLI Information - https://www.extension.purdue.edu/extmedia/ho/ho-238-w.pdf

 

Growing Calculators

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Click to visit Calculate at Maximum Grow Gardening Site.

What's in The Calculator

  • Wattage Calculator: Use this to determine the light wattage you will need for your size grow room.  
  • Parts Per Million Calculator: Use this calculator to determine accurate solution mixes.  
  • Carbon Dioxide(CO2) Calculator: Calculate how much CO2 will be needed to fill a grow room to the optimum level. 
  • Temperature Converter: Use this to easily convert between degrees Celsius and Fahrenheit.  
  • Air Exchange Calculator: Enter your grow room dimensions, and this will tell you how powerful of a fan you will need for optimum air flow.  
  • Estimated Cost Calculator: Predicts how much the cost for electricity will be monthly.

 

What's that light cost you?

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Click to visit the calculator located at Dark Sky Society

You can calculate results for up to four types of lights.

  • http://www.darkskysociety.org/lightcost/index.php
  • Select the type of lamp (i.e. Incandescent, Fluorescent, etc.)
  • Select the lamp wattage (lamp lumens)
  • Enter the number of lights in use
  • Select how long the lamps are in use (or click to enter your own; enter hours on per year).

Finally, click submit on the calculator at the site and find your answer.

 

Advanced Light Summary

The above information is compiled and commented on by me throughout this document is intended to assist you in gaining a further understanding and insight that can assist in your knowledge and help you create realistic lighting environments based on your needs and those of the plants and not necessarily the financial needs of a grow shop.  

The information is expected to assist those who are truly serious about plant lighting knowledge and using "best practice" within their growing environments for lighting.  Typically not your average grower and budget is typically not an issue for this level of hobbyist or the crop is of sufficient value to justify the expense. 

For most, I hope we played a role instilling a greater understanding of lighting and how the plants uses light throughout its development.  When "best practice" lighting is used within a "best practice" grow environment and tapered with "best practice" nutrition you can truly find the maximum range of what your genetics will create.  Achieving this is often seen as not possible for most but by understanding the "knowledge above" it will help make the complex simple.

  • As discussed lighting is as simple or as complex as you want it to be. 
    • I have seen grows as cheap as possible but competent grower and they perform better than grows I have seen of those who invested much money into the latest equipment but they did not understand how to use correctly.
      • It is a matter of knowledge and how to apply it than it is a matter of investment.
  • I thank you for your time and if this helped you, it is not me to thank as this is a combination of many who helped educate me in this art.  Puff puff and give that knowledge as you pass to others is all we ask and that is the pat on the back we gladly accept and take. 

:awesome-smiley-emoticon:

Specially for you!

 

Further advanced reading.

 

 

Next Section is Indoor Environment

http://culturalhealingandlife.com.www413.your-server.de/index.php?/topic/4-the-indoor-garden-environment/

 

 

Credits and special appreciations and respect to:

We appreciate in knowing if this helped but I like it more when their sites are visited.  We are not affiliated.

 

 

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~Hempyfan, a proud HD writing.

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