Hi, my name is Tanner main Karen. I'm an electrical engineering student here at the University of Southern Maine. I'd like to thank my instructor, Dr. Massey, for again took my project. I'd also like to thank the Undergraduate Research Opportunities Program and the main Space Grant Consortium for providing funding. My project is an LED solar simulator for use in the horticulture industry and has a tunable spectrum horticultural light, which can be made to mimic different solar conditions. A solar simulator is a device which is used to replicate the sun's intensity and spectral composition. It is important in many, including photovoltaics, horticulture, and product design, to name a few. Solar simulators are very expensive, costing thousands of dollars. I aim to design and build a solar simulator at a fraction of the cost. To design a solar simulator. This is a central to understand the qualities of the sun's radiation. The sun approximate a black body radiator at 5600 Kelvin. This can be seen on the graph on the right. The faded portion shows the unfiltered solar radiation. The unfunded portion represents what actually reaches the surface of the earth after being filtered by the atmosphere. The air mass coefficient is a scaling factor used in many industries. Compensate for the Earth's tilt in relation to the sun. Am 1.5 is the most common standard. This is due to much of North America, Europe, and Asia falling in the mid-latitudes. The AM number represents the number of atmospheres the light passes through to reach the Earth's surface. Light emitting diodes or LEDs, or electronic components which produce light. There is semiconductor device comprised of a p-n junction. The material properties of the junction will determine the wavelength of the light emitted. At the wavelength determines the color and energy of the light. The light produced from an LED is nearly monochromatic, which means that is all the same wavelength and energy. This is different than an incandescent bulb or the sun, which emits a much wider spectrum of colors and energies. As we can see in this equation. The symbol on the left, lambda is the wavelength. Since Planck's constant h and the speed of light c are constants, the band gap energy E g is the determining factor for the wavelength. The larger band gap produces a shorter wavelength with higher energy. Since LEDs are semiconductor devices, they exhibit non-linear characteristics. As we can see in this graph. As the voltage is an increase past a certain point, the current grows very quickly. This can be problematic because of the heat generated. At higher currents, higher heat will allow more current flow, in turn causing more heat. This can create a situation called thermal runaway, which will damage to LED. For this reason, it is preferable to power LEDs with constant current instead of constant voltage. So how does light measured? First, we have radiant flux, is the energy emitted per unit time. Radiant flux has the unit of watts. Photon flux is the number of photons emitted per time. Photon flux has a unit of micromoles per second. Luminous flux is the perceived brightness for human vision. Luminous flux has the units of lumens. The graph on the right shows what our vision is most sensitive in the green or yellow region and tapers off towards the blue and red. And there are some specific measurements which are useful in horticulture. Photos. In fact, photosynthetically active radiation, or par. Par can be measured two ways versus photosynthetic photon flux, or PPF. The second is yield photon flux or, or why PF. These two quantities will be discussed in the following slide. Next, we have photosynthetic photon flux density, or PPF D. This is the PPF per unit area. And finally, we have photon efficacy. This is how efficient a light source is at converting electrical energy into photons of light. All of these measurements are important to consider designing a horticulture like Let's talk about the difference between PPF and why PF lumens, as discussed in the previous slide, are poor representation for plants because lumens are a weighted quantity based on human vision. For this reason, either par or IPF are better metrics for quantifying horticulture lighting. Ppf is an unweighted value raging ranging from 400 nanometers to 700 nanometers. Why PF is a weighted quantity ranging from 300 nanometers to 800 nanometers. Ipf is weighted based on how readily plants absorb different wavelengths of light. The Emerson effect is an interesting phenomenon. When plants are exposed to both red light around 660 nanometers and far red light around 740 nanometers. The photosynthesis rate of the plants exceeds the sum of the two individual contributions. This effect can be leveraged in lighting design for more efficient photosynthesis. When we think of plant growth, we tend to think of only chlorophyll. While chlorophyll is essential for plant growth. There are many accessory photo pigment, pigments, which are photosynthetically active at varying wavelengths. Many horticulture lights tend to produce light that is catered towards chlorophyll absorption. The line heavily on red and blue light. As we see on the graph, different photopigments are active throughout the visible spectrum. Green light, which is commonly absent in many LED horticulture lights, can reach deeper into plant tissue for additional photosynthetic response. So why are LED lights becoming more common in the horticulture industry? This table shows the pros and cons and LEDs versus alternative that lighting sources, LET, LED's tend to be more efficient, produce less heat, and have a longer lifespan. These benefits come and increase initial cost. With advances in LED technology, we can expect to see the cost of LEDs decrease in the future. For my design, I chose to use for wavelengths of light. I use foil LED's of each color for a total of 16 LEDs. Leds are mounted to an aluminum heat sink using thermal adhesive to keep the LEDs at a lower temperature. They're powered with a constant current driver supplying 330 milliamps of current. I used an Arduino. And for potentiometers to control the intensity of each wavelength. I used a 15 volt power supply for both the Arduino and constant current drivers. Aircraft cable was used to suspend the light. This diagram shows how all the components are wired together. The power supply is connected to the Arduino and all for LED drivers. The LEDs are wired in series to the LED drivers. Each color has its own dedicated LED driver. The LED drivers are connected to the Arduino, to their own respective pulse width modulation pin. Pulse-width modulation is used to accomplish the dimming of the LED channels. The four potentiometer are attached to the Arduino, which control the dimming level of each LED channel independently. This setup allows for the output to be tuned to desired spectrum. These photos show various stages of the assembly process. The two photos on the right side, on the left show the LED drivers. The top picture is a single channel on one board. The bottom photo has four channels on one board. The channels are identical in function. The photo on the top middle shows the aluminum heat sink. The top right shows how each LED is attached with thermal adhesive. The bottom right photo shows all of the LEDs mounted and wires soldered. These two photos show how the cable is used to suspend the light. The photo on the left shows the LED drivers, Arduino potentiometers wired together. The photo on the right shows the housing use to hold the components and knobs for the potentiometers. This photo shows all the LEDs and operation. It is interesting to note that the far red LED looks very dim compared to the other LEDs. This is due to human vision being less sensitive to light beyond 700 nanometers. This shows the final product. To verify my design, I needed a way to test the output spectra. The spectra, this fiber-optic adapter allowed me to test the spectral composition of my light. This graph shows the results of testing each channel separately. The results show just how narrow the spectrum is for each coder. I was actually expecting there to be more overlap between the spectrums. This graph is of all the LEDs operating at full power at the same time. We can see that the blue and red spectrums are significantly more intense than the green or far red spectrums. The graph on the left is the result after the potentiometers were adjusted to match the power spectrum. On the right. You can see that the peaks of the colors represent the values on the power spectrum. Again, I was surprised how discreet these peaks are with very little overlap between colors. Ideally, there'll be better uniformity across the spectrum rather than the significant dips. The overall cost for my horticulture module came out to $265.62 sets. This does not include any of the testing equipment or tools needed to solder or assemble a module. There are many LED horticulture lights on the market that are less expensive than this, but none in this price range which allow you to tune the output spectrum of each channel independently. This research project was just a beginning step. I would like to continue the research to record additional measurements like the car uniformity and efficiency of the module. Additionally, I would like to develop lighting presets for different types of plants in different ground conditions. The graph on the bottom shows how different spectral compositions affect plant growth. The significance of my research could help create custom horticulture lights for specific plants rather than a one size fits all approach. Having fine-grain tunability of our horticulture lights, we can potentially produce higher yields, more nutritious produce, and save energy along the way. Again, I'd like to thank my instructor, Dr. Jim Massey, the Undergraduate Research Opportunities Program, and the main Space Grant Consortium. This project would not have been possible without your help. Thank you for watching my presentation. And if you'd like to ask me any questions, e-mail me at Tanner, adopt the end at main.edu.