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Stacked Container Hydroponics for Vertical Farming : Blog 5 - Lighting

RWReynolds

In this blog post, I will cover my lighting system design and implementation.

 

Available Lighting choices:

Through my research, I have determined that there are four basic types of artificial lighting used for indoor plant cultivation. These are

  1. Fluorescent - Most commonly used for used for propagation, vegetative growth, and over-wintering.
  2. High-Intensity Discharge (HID) - Most commonly used for general purpose indoor cultivation.
  3. Plasma - Most commonly used for general purpose indoor cultivation.
  4. Light Emitting Diode (LED) - Most recently developed grow light technology. Commonly used as supplemental lighting along with natural and other artificial grow lighting. Also used alone for general purpose indoor cultivation and bloom promotion.

Chosen lighting:In my system, I have chosen to supplement natural sunlight with LED lighting for these reasons.

  1. Cost. Natural lighting is free and can be used effectively if plants can be arranged near windows, skylights or in greenhouses. Both the cost to purchase and operate LED lighting is much lower than for any of the other types of artificial lighting. LED grow lights have been in development and testing, and used in production environments, for many years now and have proven to be very successful under the right conditions. A large part of my decision to use LED lighting, and the specific product I chose, is simply due to the initial purchase price. As I am working within a relatively tight budget for this project, the initial cost had to be the main deciding factor.
  2. Space requirements. Natural sunlight requires no additional space. LED grow lights can be installed in a very small footprint. The lights I have chosen provide a total lighting surface area of approximately 650 square centimeters. The system is arranged vertically and the actual dimensions are approx. 1m tall by 6.5cm wide. This will provide supplemental lighting for 6 to 7 vertically stacked planting areas, sections within a single planting container, at any given time. This equates to 6 or 7 to 12 or 14 actual plants. The footprint of the system is approx. 460 square centimeters. As one of the main criteria of the challenge is vertically oriented cultivation, which equates to reduced footprint, I think my system meets that criteria quite well.

 

Overview of my lighting system:

I will be using natural sunlight supplemented with LED grow lighting. The cultivation unit will be placed in front of a window that will receive relatively direct sunlight during most of the daylight hours. The vertically oriented LED lighting will be placed on the opposite side of the cultivation unit from the window. As the cultivation unit is rotated continuously throughout the day plants will receive both direct natural sunlight and artificial lighting. Meaning all plants will receive either sunlight or artificial light during the entire daylight hours period. During dark hours, the cultivation unit will be rotated periodically to provide pre-determined periods of artificial lighting. Over an approx. 12 hour period of dark each stack of planting areas should receive an additional two hours of artificial lighting as well as some additional time where they receive defuse artificial lighting. I think I could increase the dark hours light received by introducing reflective materials placed opposite the artificial lighting. However, this would have to be manually removed and put in place in the morning and evening. As I am trying to keep the system as automated as possible, I will not do this unless deemed absolutely necessary. Also, if I can work out how to read ambient light from the sensor-puck via an RPi then I can base the lighting schedule on the change in morning and evening ambient light.

 

LED lighting system details:

As my LED lighting is only being used to supplement natural sunlight, the quality, power nd spectral output, of the LED light may not be as critical as when using artificial lighting exclusively. It is difficult to know the exact output power and spectral output of an artificial lighting system if it is not, truthfully, provided by the manufacturer. To do this requires some relatively specialized and expensive equipment that I do not have access to. So below is my best estimate using the information provided by the manufacturer and data I have gathered in testing.

 

Configuration: The physical configuration of the LED arrays I'm using is strips of 36 total (27 Red and 9 Blue) LEDs. Each strip is 0.5m in length and approx. 1.3cm in width. They are sold in kits of 5 strips for $35 per kit. I am using two kits. See the picture below.

image

I have mounted the strips on a  9.5mm x 6.5cm x 1m plywood backing strip. Each kit is mounted five across. Then I've attached the plywood backing pieces to PVC pipe with the two kits being mounted one above the other using a PVC coupler. See the picture below. I am using an old modified guitar stand to support the entire structure. It turned out to be quite stable and adjustable. See pictures below.

imageimageimage

 

 

Power output: Using a simple multimeter I have determined that my LED light array draws a total of approx. 5A @ 12VDC. So the input power is 60W. The manufacturer claims a power factor of 97%. Since the concept of power factor doesn't apply to DC circuits, as the have no reactance, then the term power factor doesn't really apply. So I'm assuming they are referring to power efficiency, or that input power which is actually seen in the output of the circuit. I don't know this for sure. So I believe the total output power of the array should be approx. 58W.

 

Currently, the light strips are connected such that each corresponding top and bottom strip is in series while the five sets of two are in parallel. I could probably get a little more power out by connecting all strips in parallel. But the series/parallel combination turned out to be very convenient and I believe I have enough power output for the application.

 

Spectral output: The lights I have chosen do not produce the absolute optimal spectral content. They are made up of only two colors (wavelengths). These being Red @ 660nm and Blue @ 445nm. Red light promotes photosynthesis, which are beneficial while plants are growing and flowering. While blue light promotes the synthesis of Chlorophyll and Carotenoid, which are benneficial for promoting the leaf growth.

 

In a subsequent blog I intend to go into more detail concerning the cultivation requirements including lighting and nutrient requirements. In this blog I simply wanted to present the design and implementation details for my chosen lighting system.

 

As always, happy vertical farming and good luck to all the challengers.

 

 

Cheers,

Rick

  • Nice update and a good start with the LED lighting.

     

    I also liked your discussion about the spectral content verses light intensity.

     

    DAB

  • in reply to RWReynolds

    Hi Rick

     

    I have a couple of considerations image, as usual. I am far away to be an expert or also have a minimal knowledge on this world of the vertical farming, as you know, so I mix logic, some intuition and my historical experience in normal terrain cultivation, a world I was used for my first 20 years of my life.

     

    The first though is about the LED lighting usage. If I was doing something like your illumination system (that sounds nice AFAIK), I will place a diffusor to make less direct rays of the light (a plastic opaline white transparent surface or similar).

     

    Then about the measurement. To reach a reasonable quality in light measurement without investing too much, I think that if you orient your search in the environment of the monitor calibration systems, based on the LED pixels and lighting you have two advantage: the first is that there are almost precise tools at a very reasonable price and the second is that you can create a digital correspondence of the exact colour with the proper combination of RGB on the screen (e.g. a monochromatic wide square) and compare the light intensity with the reference that is always a good weighting system.

    Last thing is a persona approach: I trust always no more than 80%-90% on the theory formalisations. Taking in account the right average distance (i.e. 24"), the average colour (or light frequency) and the expected intensity, you know that remain a lot of subjective parameters strictly influenced by how your specific structure you are using. So for example a light strip (like I saw on the photos) maybe great to make a first "lab" growing experiments simply placing it with a slant so the lower plants are the nearest and the upper plants are at the max distance. Then in just a week you immediately see what is the more responsive distance and intensity in your specific case, with exactly that lettuce type etc.

     

    I hope I was sufficiently clear explaining these concepts due my wrong English.

     

    Enrico

  • in reply to amgalbu

    In my research, I did find numerous websites suggesting exactly how much, and what type of, light is optimal for the cultivation of various types of plants. It seems that raw output wattage is not the greatest deciding factor in what's optimal. It has more to do with the correct amount of light within very specific bandwidths.This is how I determined that the use of red and blue LEDs was the correct choice.

     

    This is not an area in which I was particularly eknowledgeabl before the challenge. This is what the I discovered:

     

    In plant cultivation using LED lighting the PAR (Photosynthetically active radiation) value of light is much more important than the measure of pure output wattage. I borrowed the following from a Wiki on grow lights.

    "PAR is the actual light energy that is of value to the plant to promote growth. Typically, the PAR value of a light is measured using a precision           PAR meter (Light Quantum Meter) at 24" below the light surface, approximately the optimum distance between the light and the growing tip of the     plant. Measurements are in μmoles/m2/sec. Light intensity is also important, a comparison of the lumens produced by a light is indicative of the         energy available for the plant, so comparing light sources with PAR and/or lumen output may be a more correct comparison between terrestrial         grow lights."


    Unfortunately I have to rely on the manufacturer's and seller's stated specifications for the lighting I choose to purchase. I certainly don't have access to the equipment required in order to test the lighting myself. And in this day of The Internet I also relied heavily on the customer reviews of the porduct.. Assuming at least someone out there knew more about the details than I. image


    I have one more blog post planned that will cover the SCADA (supervisory control and data acquisition) system for my design. After that we sould be into the actual germination/growing cycle. During that period I plan to create several blogs concerning the detail of the challenge cultivation requirements, how I've tried to meet them, where I think I may have fallen short and what I might do to correct it during the growing period.


    Cheers,

    Rick

  • Hi Rick

    Nice update!

    I have one curiosity: is there a way to estimate the optimal amount of light required by a plant? I mean, you could put LEDs that drain 3000W to make plant grows at the fastest possible rate, but that is probably going to be a waste of energy because most of the light will not be absorbed by leaves...