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LED Growlights : The Mars BioPod v1

Overview

As part of the Mars BioPod v1 construction, we going to use LED strip lights to provide round the year growing and as consistent as we can growing environment. If we were on Mars, we might not want to use sunlight directly because we don’t want the harmful radiation that is present because of the lack of an atmosphere.

Because we have water nearby, we’re going to use components that are all IP67 or greater. The IP code is the International Protection Rating that is defined by the International standard IEC 60529 (see https://en.wikipedia.org/wiki/IP_Code) that classifies the degrees of protection from dust and water and alike.

The first digit indicates the level of protection against solid foreign objects, where 6 provides the top level of protection against dust. The second digit is the protection the equipment offers against harmful ingress of water. The top levels of the second digit are defined as:

IP NumberFirst Digit - SolidsSecond Digit - Liquids

IP66

Protected from total dust ingress.

Protected from high pressure water jets from any direction.

IP67

Protected from total dust ingress.

Protected from immersion between 15 centimeters and 1 meter in depth.

IP68

Protected from total dust ingress.

Protected from long term immersion up to a specified pressure.

Seeing as we potentially have hoses and alike around, I’m going to be going for a setup that offers IP66 and above protection. For our LED strips, the construction options (in terms or IP24, IP65, IP67 or IP68) were as follows:

Diagram showing IP64, IP65, IP66, IP67 and IP68

We’re going to use Robotechy 12V DC rigid strips lights, so that if in the future we want to run this off a 12V battery (such as in a solar powered setup) then we could do this. This is something I would like to look at in the future.

LED Specifications

In our setup we're using rigid LED strips of various colours so that we can mix and match as we see fit, rather than a particular setup that we are fixed with. The rigid strips provide a convenient way to waterproof and mount our LEDs.

In our setup, we are going for 8 rigid LED strips, with ratios of Far-Red (1) : Red (4) : Green (1) : Blue (2). The exact ratios come from research (see links at the bottom of this page from NASA research with Veggie on the MIR Space Station) to promote maximum green growth. It should be noted that a lot of this has actually also been pioneered from indoor marijuana growth from what you find on the internet.

Steve Wanson on the MIR space Station with Veggie

Veggie weighs 7.2 kg and requires 115 Watts of power. While stowed Veggie requires 0.02 m3 and deployed it requires 0.11 m3 of space. Veggie has a growing area of 0.16 m2 with a maximum growth height of 45 cm. The hardware is cooled with cabin or avionics air. The Veggie light sources are red (640 nm) 300 micromole/m2/s, green (540 nm) 30 micromole/m2/s and blue (440 nm) 50 micromole/m2/s. From http://www.nasa.gov/mission_pages/station/research/experiments/Veggie.html

From the diagram below you can see that plants need particular requirements for photosynthesis.

Absorption rates of light wavelengths for vegetative and flowering plant growth

If you were going for more flowering growth than vegetative growth, then you would probably want more red light.

The use of roughly 10% green light has been shown to improve growth, as well as allow for better inspection of the plants (as plants generally look green because they reflect green light, if there is no green light they look rather black!).

Rigid LED Strip NamePowerColourWavelengthsVoltageLED Chip Name

Robotechy BioLED-18-440-460

18 x 1W Blue 440nm - 460nm 12VDC San-an LED Chips

Robotechy BioLED-18-540-560

18 x 1W Green 540nm - 560nm 12VDC San-an LED Chips

Robotechy BioLED-18-640-660

18 x 1W Red 640nm - 660nm 12VDC San-an LED Chips

Robotechy BioLED-18-710-720

18 x 1W Far-Red 710nm - 720nm 12VDC San-an LED Chips

The wavelength characteristics of the LEDs above are as follows:

LED Grow-Light Circuitry

I am not an electrician, please consult a qualified electrician when dealing with high voltages and currents.

I did consider using a 24VDC power supply with a 2 by 4 series-parallel setup, but if one of the circuits burnt out or otherwise, I would blow the other too as that side would get all the 24VDC, hence best to stick with 12VDC. As you can see below, we are going for the 8 strips to run in parallel (each grey rectangle defines an LED strip, which inside includes a resistor and 18 LEDs). The voltage across each strip is therefore 12V DC, so we are getting the maximum brightness out of each strip.

Mars BioPod v1 LED Circuit Schema

We’re going to use the SANPU LED 12V 16.6A 200W constant voltage power supply. This unit is IP67 rated so offers good level of protection against water as operates from -20 to 60 degrees so should be fine outdoors. The efficiency is apparently 85% which means it should be good to power up to 200 x 0.85 = 170W. As each LED strip consists of 18 x 1W = 18W, we can see that it should be possible to run up to 170W / 18W = 9 strips, so using 8 gives us a bit more of a buffer if the power or efficiency should not be quite as labelled.

I am happy to confirm that the draw of current is very close to the 18W x 8 = 144W. Some on the market I have seen reviews of although they say each LED is a certain wattage, they do not draw that power, and thus, not deliver the energy to the plants intended with reduced growth. In addition, LEDs are often labelled with the wattage of a comparable bulb rather than what they draw themselves to confuse matters.

Don't overload your circuit. If you plan on connecting multiple Mars BioPods onto a ring circuit, check what is already loaded onto the circuit and that your ampage drawn does not exceed the rating of the circuit. Consult an electrician (I am not one).

Components

Below are the list of components that we will be using in the build of this solution.

Build Steps

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Here is step 1

Here is step 2

Related Research

If you want to read up more on what NASA are doing and/or the thinking behind the LEDs used in our setup, then see some of the links below:

With the advent of long-duration space laboratories such as Mir and the International Space Station (ISS) it has become clear that more emphasis needs to be placed on improving the human habitability of these environments. The Vegetable Production System (Veggie) provides a means to supply crews with a continuous source of fresh food and a tool for relaxation and recreation. Veggie will study crop productivity, air and water revitalisation with reduced logistical and operational resources compared to other plant growth systems.

Veggie weighs 7.2 kg and requires 115 Watts of power. While stowed Veggie requires 0.02 m3 and deployed it requires 0.11 m3 of space. Veggie has a growing area of 0.16 m2 with a maximum growth height of 45 cm. The hardware is cooled with cabin or avionics air. The Veggie light sources are red (640 nm) 300 micromole/m2/s, green (540 nm) 30 micromole/m2/s and blue (440 nm) 50 micromole/m2/s.

To find out more, see: http://www.nasa.gov/mission_pages/station/research/experiments/Veggie.html

Veg-03 is a direct follow-on to the Veg-01 hardware validation test. The primary goal of the Veg-01 hardware validation test was to demonstrate plant growth in the Veggie facility. ‘Outredgeous’ red romaine lettuce plants were grown in two different sizes of arcillite, a calcined clay media. The completion of the first run of Veg-01 helped investigators compare root zones of two media sizes to determine water and root distribution within the different sized-particles to provide recommendations for future Veg series investigations. Shoot tissue samples provided information on the microbial load of the plants. Photographs taken during the first run helped in the assessment of plant growth rates, as well as plant health. Two data loggers recorded the temperature and relative humidity within the Veggie facility. Crew questionnaires provided insight into the appropriateness and thoroughness of the crew procedures for the Veggie facility and plant growth operations. Although plant pillows performed well, modifications are necessary for future watering procedures. Veg-03 tests the performance of the water delivery system with modified procedures, and a different crop with different water requirements than that of the ‘Outredgeous’ red romaine lettuce.
 
Plant pillows are single use items, thus reducing the chances of microbial contamination of the Veggie facility and produce. A major aspect of the Veg-01 hardware validation test was to collect baseline microbial data from plants and plant pillows grown in the Veggie facility on ISS. Ground testing has demonstrated very low microbial levels on lettuce plants grown in the ground Veggie facility. Preliminary flight tests conducted on the Veg-01 returned samples indicated fairly low microbial levels without specific pathogens. Discussions with space microbiologists, flight surgeons, and space food technologists indicated that the crew should be able to consume the fresh produce with precautionary sanitising using on-orbit Prosan wipes since microbial levels in the returned samples were sufficiently low. Preparation is underway to formally document that concurrence. The baseline data collected from both the Veg-01 and Veg-03 flight experiments are a resource for future Veg series investigations. This information provides data on necessary procedural changes, hardware upgrades, or horticultural options, as Veggie becomes an integral part of ISS expeditions in the future.
The overall goal of Veg-01 is to demonstrate proof-of concept for the Veggie plant growth chamber and the planting pillows. This research builds upon hardware development via an SBIR grant to ORBITEC for the initial prototype Veggie units with subsequent hardware development for next-generation units. Both ORBITEC and KSC have been involved in plant growth optimization of the Veggie hardware and testing and collaboration have resulted in the development of the pillow planting concept to interface with the Veggie hardware. Through numerous tests the VEG-01 science team has refined the pillow concept and selected growth media and fertilisers, plant species, materials, and protocols for using the pillow concept in Veggie to grow healthy plants that can provide crew with food and recreation. The pillow concept is designed to be low mass, modular, require no additional energy and be very low maintenance. Pillows of different sizes have been designed to accommodate a wide variety of plant types and different types of growing media.
 
The primary goal of the Veg-01 testing will be to demonstrate plant growth in the Veggie hardware using lettuce as a test species. One set of Zinnia seeds will also be flown to test a long duration growth of a flowering plant in the VEGGIE facility. Plants will be grown in two different sizes of arcillite, a calcined clay media. This test will help us compare root zones of the two media sizes to determine water and root distribution in the different sized-particles to provide recommendations for future Veggie investigations. Shoot samples will also provide information on any growth anomalies when compared with ground controls and will provide information on microbial growth and food safety. Photographs will be used to assess plant growth rates and plant health. A data logger will record the environment within the Veggie hardware. Crew questionnaires will provide insight into the appropriateness and thoroughness of the crew procedures for Veggie hardware and plant growth operations.
 
Pillows are single use and thus reduce the chances of microbial contamination of the Veggie hardware and produce. A major aspect of the proof of concept flight, Veg-01, is to collect baseline microbial data from plants and pillows grown on the International Space Station (ISS). Ground testing has demonstrated very low microbial levels on lettuce plants grown in Veggie-relevant conditions. Discussions with space microbiologists, flight surgeons, and space food technologists at JSC indicate that if microbial levels are sufficiently low the crew could consume the fresh produce without sanitizing. For crops that naturally have higher levels of microorganisms (e.g. radishes, which grow in contact with water and nutrients) a space-rated produce sanitation method must be developed and tested.
 
The baseline data collected from the Veg-01 flight will be a resource for future Veggie investigations. This information will provide data on necessary procedural changes, hardware upgrades or horticultural options as Veggie becomes an integral part of ISS expeditions in the future.
With the long-duration missions aboard the International Space Station (ISS), it has become clear that more emphasis needs to be placed on improving human habitability. The Vegetable Production System (VEGGIE) provides a means to supply crews with a continuous source of fresh food and a tool for relaxation and recreation.
 
VEGGIE can support a variety of experiments used to determine how plants sense and respond to gravity. The plants will be harvested for further investigation and consumed by the crew members.
 
VEGGIE's growth volume will be the largest volume available for plant growth on ISS. This will enable growth of larger plants that were previously not grown on ISS due to size restrictions. Additionally, the large, adjustable LED light bank makes VEGGIE an ideal facility for other experiments requiring a temporary light source.
 
As with all basic research, an improved understanding of plant growth and development has important implications for improving plant production on Earth.

If you plant it, will it grow—in microgravity on the International Space Station? Expedition 39 crew members soon will find out using a plant growth system called “Veggie” that was developed by Orbital Technologies Corp. (ORBITEC) in Madison, Wisconsin, and tested at NASA's Kennedy Space Center in Florida.

For more information, see: https://www.nasa.gov/content/veggie-plant-growth-system-activated-on-international-space-station

Find out more about the benefits of far-red lighting in particular when growing leafy greens. NB In our simple set-up we are not able to vary the far-red to give more far-red at the end of the day for example to simulate sunset.

For more information, see: http://leds.hrt.msu.edu/assets/Uploads/Univ.-of-Arizona-Greensys-FR-EOD-presentation-2011.pdf

Summary

So there we have it, this is how we're providing the required lights for photosynthesis.

What variations would you make to this setup? Any different LED wavelength choices?

About the author

I am a nerd by trade, and run my own company (Webtechy Ltd) specializing in Microsoft technologies such as Azure, SharePoint and Office 365 as well as other content management systems. I also enjoy graphic design in PhotoShop and tinkering around with Arduino's and Raspberry Pi's. In my spare time I like to go to the gym, running (well, I say "enjoy"), and martial arts.

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