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Revision as of 23:34, 17 October 2018
Alternative Roots
Hardware Results
RESULTS
Introduction
Having assembled our hydroponics system, it needed to be tested to quantify performance. This involved measuring the light intensity that the LEDs output to determine the lux ranges possible. We also investigated whether it was possible to germinate seeds and to grow seedlings in our system.
Lux Levels
The first task was to measure the light intensity generated by the LEDs. This would inform us if the possible range was suitable for seed germination and plant growth. For example, on an overcast day lux produced is between 1,000 - 30,000 [1]. We used a lux sensor to initially determine which settings gave specific light intensities. From this, we were able to experiment with different colours of light. Through research carried out as part of our Human Practices, we expected that purple light would give us the greatest lux since this is the most commonly used in the contained plant growth industry.
Our initial tests were to run the pre-programmed colours i.e. blue, green, purple, red, White and a rainbow function which cycles through the spectrum. Firstly, we decided to measure the 'rainbow' function. We applied this test so that we could determine a range which may give us the highest lux. We established that purple/blue is the 'optimal' colour to use peaking at 1100 lux, confirming what our Human Practices has revealed when visiting various hydroponic facilities.
Next, we loaded the Arduino with a programmed in 'purple' colour. This measurement stabilised at roughly 1000 lux. Leading us to believe we could tweak this light level. Therefore we tried different pre-set colours; blue, green, red, white, giving roughly; 1375, 300, 525, 1360 lux respectively. Realising that the LEDs manage colours by producing different quantities of blue, green and red light, we figured we may be able to create an optimum between these colours hopefully improving on the pre-set Blue. This means we could not use a pre-set library and would have to define the light levels of the primary colours manually.
Before starting, we defined the brightness of each colour as an 8 bit integer (265 light levels). The most obvious place to start was to turn all the primary colours up to 265. Producing altered white light which performed worse than the pre-set blue and white at roughly 1300 lux. Therefore we created purple via blue and red at 265 (altered purple). This also proved to be less than the pre-set blue but slightly higher that ‘altered white’.
Therefore, thinking that the pre-set blue was actually our maximum, we attempted one further test. This held blue at a constant 265 but varied red from 0-265. On plotting the results, we discovered that there is a lux peak when the red is at a light level of 129. Next we tried blue:265, red:129 with a varied green from 0-265. This appeared to have a detrimental effect on the light intensity. Figure 2 shows the relationship between these colours.
Conclusion
From these measurements we can determine that the lux level should be adequate to germinate Arabidopsis thaliana, rocket and various other plants. Heating control does not need to be built in as this system will be held inside a room with a constant temperature. Also, water and air flow are not a pressing issue since the water needs to be changed once a week. We therefore felt that we had gained sufficient understanding of our how our hardware operates to proceed with growth experiments.
Growth Experiments
Introduction
In order to understand the performance of the NH-1, two experiments were conducted. The first experiment was conducted to determine the range of conditions that the system can generate. This was a proof of principle experiment, which is meant to outline that different conditions can generate different phenotypic responses in the plants. The second experiment measured the percentage germination from the optimal purple light conditions of the NH-1 against natural light conditions.
Method
For the first experiment we had to make a simple barrier to place inside the NH-1 in order to block light effectively. We did this by taking off-cuts of plywood and wrapping them in tinfoil to create a reflective surface, sourced from the architecture workshop. Figure 3 shows the dividers used. This allowed us to expose different areas of the hydroponics to varying wavelengths of light by addressing individual LEDs.
Utilising the Arduino's easy-to-adapt design we can manipulate this device to display the desired wavelengths at each individual LED. The first four LEDs emitted green light and the remainder emitted purple (separated by a divider), the intensities were measured to be 200, 1700 lux respectively (code can be found
here). Eruca sativa Seeds were then planted in two pipette-tip racks (96 in each), one green (A), one purple (B). They were then left to germinate for a week.
Results
After 1 week the seedlings were checked for germination (Figure 4) and had their height measured (Figure 5). The results show that a greater percentage germination was obtained from purple light (22/96) than green light (4/96). Out of the 4 seedlings that germinated in green light, the seedlings were much taller than those in the purple light, though those grown in purple light were more uniform in their growth, showing the ability of the NH-1 to elicit a range of phenotypic responses and thus fulfilling its design purpose.
Figure 4. The percentage germination of Eruca sativa seedlings after 1 week in green or purple light.
Figure 5. The mean height of Eruca sativa seedlings after 1 week in either green or purple light. Error bars show the standard error of the mean.
Figure 6. The percentage germination of Arabidopsis thaliana seedlings after 1 week in the NH-1 or on the laboratory windowsill.
The second experiment concerned comparing the NH-1 to laboratory conditions. The results show the percentage germination in NH-1 after conditions after 4 days was over 50 % compared to approximately 25 % in laboratory conditions. After 8 days over 90% of the seedlings had germinated in the NH-1 compared to approximately 60 % in laboratory conditions (Figure 6).
Conclusions
Both of the experiments provided data that suggests our system is effective at creating a high throughput growth and germination environment for plant research, not only did Arabidopsis thaliana seeds germinate in the NH-1, but the rate of germination is greater than that of laboratory conditions with the added advantages of being programmable and a controlled environment allowing greater standardisation. Within the system we were able to create a range of growing environments that elicited different phenotypic responses in Eruca sativa seedlings showing the range of possibilities the NH-1 provides for researchers interested in high-throughput plant research.
.References & Attributions
Attributions: Luke Waller, Umar Farooq and Lewis Tomlinson
1. Pattern Guide; 17 Apr 2011, https://patternguide.advancedbuildings.net/using-this-guide/analysis-methods/lux-overcast-sky