DIY Grow LED Light | Designing a Better Sun

Are you frustrated with the prices for high quality grow light systems?

To be fair, most of the commercial LED lights on Ebay & Amazon are totally sh*t that perform like Christmas lights rather than high quality good spectrum photon delivery systems.

In this tutorial, I try to show the steps in designing a custom LED grow light, and briefly prove the results of my indoor hydroponic setup irradiated entirely by the DIY lights.

Advantages:

• Open source
• Easy to replicate
• Basic available components
• Easily customized for different plants & environments
• CHEAP (~40$)
• IT DOES WORK!

Tools & Materials

Cree LED chips

• 3W Royal Blue (450nm)
• 3W Deep Red (660nm)
• 3W Far Red (720nm)
• 3W UV (365nm)
• 3W Green (520nm)
• Aluminum Heatsink
• MOSFET (IRL2203N)
• Adjustable DC-DC voltage regulator
• RTC module (DS3231)
• Arduino (any version)
• Fan (optional)
• 12V DC Power Supply (min. 5A)
• Thermal Adhesive

MOTIVATION & Good Mood :)

Introduction

After my first tutorial about Grow It Yourself (GIY), where I share my experience in building an integrated smart growing system, I decided to dive deeper into plant science, and try to use my tech skills to come up with a solution on a more fundamental level

GIY system, as beautiful as it looks, had a few drawbacks that was limiting its feasibility on the real market. One important issue was the light

Light is one of the most important factors for plant growth and development, regulating plants’ photosynthesis, metabolism, morphogenesis, gene expression, and other physiological responses. Modifying the light wavelength, photon flux (quantity of light), and photoperiod lets one to adjust biomass accumulation, flowering time, stem elongation, and nutritional quality

Light is the primary factor that determines the outcome of the crop, aka its value! There are many organizations that focus on horticulture lighting, leaders on the grow light market such as Philips, Illumitex, Valoya, SananBio, Osram, Samsugn etc. but the main issue remains the high price!

So, that's exactly what we try to tackle here))

The indoor farming, urban agriculture, vertical farms - are still a new and emerging trends with a huge potential of being one of the many solutions to solve food scarcity and feed the future population. However, the next Agricultural Revolution has to be based on collaborative effort, and I strongly believe that open-source & maker community is the right place to start!!!

Background

*This will be a long but informative chapter describing the WHY behind this tutorial. I will explain relevant terms and concepts necessary to have a broader understanding, as well as reveal the common myths and misconceptions about Grow LED Lighting

Skip directly to the DIY instructions if irrelevant

So, to be honest, this is a quite broad and complex topic that requires thousands of pages to have a good understanding. However, I will try to keep short and share some basics into this mysterious world))

Light characteristics that influence pant growth and development are commonly attributed to intensity, quality, uniformity, direction, polarization, coherence, and pattern of illumination. Light serves as energy source for plant growth and development through photosynthesis, but through photoreceptors, light regulates some morphogenetic processes such as flowering, stomatal opening, leaf expansion, plant elongation and circadian clock.

Chlorophylls, along with carotenoids, are the most abundant photosynthetic pigments that drive photosynthesis in higher plants. Chlorophyll exists in two forms— chlorophyll a and chlorophyll b. Chlorophylls absorb light between λ400 and 700 nm, known as photosynthetically active radiation (PAR) or photosynthetic photon flux density (PPFD), with the main peaks of absorbance in the red (λ600–700 nm) and blue (λ400–500 nm) regions of the spectrum. Nevertheless, plants can use most of the light within PAR region for photosynthesis due to the other pigments (e.g., carotenoids), which can efficiently capture the light that is poorly absorbed by chlorophyll.

MYTH #1 - from the information above, we can derive the origin of the common misconception that only RED & BLUE light is necessary for photosynthesis because of the chlorophyll a and b. However, as mentioned above, chlorophyll is not the only pigment that reads information from the light source!

The conclusion is: If you use Red/Blue LEDs to irradiate a greenhouse that is mainly irradiated by sun, you will boost the overall performance due to the peak wavelengths of red (λ600–700 nm) and blue (λ400–500 nm). If you use Red/Blue LEDs as the main & only lighting source for your indoor farm (no access to other lighting sources), then you limit a lot the overall performance of the plants

Color rendering index (CRI) is a quantitative measure of the ability of a light source to reveal the colors of objects in comparison to natural light. Using CRI you can estimate how comfortable the light is to human eyes.

Colour temperature (CCT) value is used to describe the color of a spectrum. Generally the value is only used to describe different color schemes of white light.

• CCT > 5000 K are called cool colors (“bluish white”)
• CCT < 3000 K are called warm colors (“yellowish white through reddish white”)

MYTH #2 - CCT and CRI are introduced from the lighting industry to describe light sources based on human vision (peak at 555 nm). Hence, CRI and CCT are not useful measures for light sources used in combination with plants. One cannot derive growth performance, phenotype or morphological changes.

The light intensity in agriculture is a measure of the PPFD and quantified as μmol photons m-2 s-1, that is also simplified to μmol m-2 s-1 in the range of PAR, which designates the radiation spectrum between 400 and 700nm that higher plants are able to use in the process of photosynthesis. Daily light integral (DLI), the product of PPFD and photoperiod, represents the total photosynthetic photon flux (PPF) emitted by a light source in 24h, and commonly has a linear relationship with plant biomass and accumulation of nutrients

DLI = PPFD × photoperiod

Light quality refers to the composition of the light spectrum that will induce different responses and play a decisive role in plant growth and development. Additionally, the light quality impacts the primary and secondary metabolism, affecting the carbohydrate and nitrogen metabolism, the production of color, flavor, volatile and aromatic compounds, nutritional quality, as well as plant defense mechanisms

UV (200nm - 400nm) - PROTECTIVE MEASURES to high light conditions and stimulation of insect repelling chemicals. Enhances pigment accumulation in leaves, affects leaf and plant morphology.

Blue (400nm – 500nm) - Signal for lack of neighbors, no need to compete for light. Stimulates stomatal opening, stem elongation inhibition, thicker leaves, orientation to light and photoperiodic flowering.

Green (500nm – 600nm) - Signal of neighbors, competition for light. Responses opposite to blue light; stomatal closure, some shade avoidance symptoms, enhanced photosynthesis in deeper cell layers

Red (600nm – 700nm) - Lack of neighbors signal. Main component needed for photosynthesis, stem elongation inhibition, signal light

Far-red (700nm – 800nm)- Signal light; Signal of neighbors, competition for light. elongation, flowering

*By changing the R:FR and B:G ratios in a spectrum we can manipulate plant growth

MYTH #3 - Don't forget about the Green light! Even though green light has rarely been considered as a biomass-promoting waveband and is frequently disregarded as useful for photosynthesis because of the minimal absorption by chlorophyll pigments, recent reports suggest that it can have positive direct and indirect impact on plant development and photosynthesis.

Accordingly, it was found that red and blue light drive CO2 fixation mainly in the upper palisade mesophyll of the chloroplast, while green light drives CO2 fixation in the lower palisade. Similarly, was proved that with increased PPF, green light can improve photosynthesis by penetrating deeper into the leaf and driving CO2 fixation of inner chloroplasts once the upper chloroplasts of individual leaves are saturated by the white light. Green light considerably contributes to photosynthetic carbon assimilation and is essential in stimulating biomass accumulation in deeper sections of the leaf and lower canopy, where red and blue light are almost depleted.

Green light also sends a strong signal to the leaf, enabling tighter control of adaptation to a shaded or changing light environment, and potentially increasing water-use efficiency within canopies

While developing LED lighting systems for space missions, scientists at NASA found that the combination of red and blue wavelengths produced a harsh purple light that caused plants to look grey/black, making difficult for workers to assess the health status of the plants. However, according to the author, the plants appeared green and visualization of any pests, disease, or nutrient deficiency was much easier after adding some green proportions to the light recipe. It was also found that the addition of green light positively influenced the plant yield

I think we can stop here, before it got even more confusing :D Now let's talk about things we need to know before building the actual LED system!)

Driving LEDs

Because LEDs are low-voltage DC sources, they need a special set of electronics to convert the AC that flows through power lines into a usable and regulated DC form

Switching regulators, also known as “DC-DC”, “buck”, or “boost” converters, are a good way to drive LEDs. Switching regulators can either step-up (boost) or step-down (buck) the power supply input voltage to match the voltage needed to power the LED. It continually controls the current and adapts to keep it constant with 80-95% power efficiency

Many AC-DC drivers have been brought to the market to simplify the process of powering LEDs. There are two main types of LED drivers, the ones that use high voltage AC input power (typically 90V – 277V), also called Off-Line drivers or AC LED drivers, and those that use low voltage DC input power (typically 5V – 36V). In most cases, low voltage DC drivers are recommended due to extreme efficiency and reliability

Thermal Management

Even though LEDs are cool when touched, they generate plenty of heat due to inefficiency of the semiconductors that produce light. The total radiant efficiency (optical output power in form of light divided by total electrical input power) is usually between 5% and 40%, which means that 60% - 95% of the input power is lost as heat. As the internal temperature of the LED increases, the forward voltage and light output decreases, causing the LED to draw more current. This affects not only the brightness and efficiency of the LED but also the overall lifetime. Eventually, the LED will continue drawing more current and getting hotter until it burns itself out, the phenomenon known as Thermal Runaway

In order to keep the LED temperature low, there are two thermal management solutions available: passive and active cooling techniques

Passive cooling, commonly used in LED fixtures, achieves a high degree of natural convection and heat dissipation using a heat sink. Heat sinks play an important role in LED lighting because provide the path for heat to easier dissipate from the LED source to the environment. The efficiency of heat dissipation is directly affected by the thermal conductivity of the heat sink material, the best being copper, but due to its price point, aluminum is widely used for the majority of heat sinks

On the other hand, active cooling relies on external device to increase the heat transfer through a higher rate of fluid flow, which dramatically increases the rate of heat dissipation. Solutions for active cooling include forced air using afan or blower, forced liquid, and thermoelectric coolers, which are used when natural convection is not sufficient to keep the temperature low. The big disadvantage of active cooling is the need for electricity, which results in higher costs as compared to passive cooling solution

Dimming Techniques

The total light output of an LED is determined by the amount of current flowing through it, and by controlling that current, the level of the LED brightness can be easily adjusted

Low voltage DC drivers can be controlled using several different ways. The simplest solution to dim LEDs is using a potentiometer, which is basically a resistor with a rotating contact that forms an adjustable voltage divider that gives a full range of 0% – 100% dimming

Another optimal solution is pulse-width modulation (PWM), which switches the current sent through an LED on and off at a high frequency (several thousand times per second), and the time-averaged value when the LED is on and off will determine the brightness of the LED. The LEDs can also be dimmed through constant current reduction (CCR), also called analog dimming, which is an efficient and simple method of LED brightness control

Both PWM and CCR dimming methods have their advantages and downsides. The commonly used PWM technique has a broad dimming range and can control the light output with a high precision. On the other hand, it requires complex and expensive electronic equipment to produce current at a high enough frequency to prevent flicker. CRR dimming is a very efficient method that does not require expensive electronics and allows drivers to be located remotely from the LED light. However, CRR is not suitable for high precision dimming where light levels below 10% are required

Assembling the LED Panel

To start with, I prepared all the necessary LED chips that were ordered in advance, which are Royal Blue (FV: 3.2 – 3.6V; FC: 350 – 1000mA), Deep Red (FV: 2.2 – 2.4V; FC: 350 – 1000mA), Green (FV: 3.2 – 3.4V; FC: 350 – 700mA), and Far Red (FV: 1.8 – 2.2V; FC: 350 – 700mA)

The beautiful part about that is easy customization. I decided not to use the UV light in my assembly, but to add any other spectrum to the LED panel is quite easy, a matter of adding a new set of LEDs such as UV, warm/cold white, or any other color. Hopefully you got the logic here))

Each LED was connected in series with a MOSFET (IRL2203N, TO-220) and controlled by pulse width modulation (PWM) signal coming from Arduino MKR1000, which resulted in full control over each separate LED array in the LED panel

All the LEDs were attached to a 15x15cm aluminum heat sink using the thermal tape to ensure an even heat distribution and avoid overheating, and driven by a DC 12V 20A power supply, connected to an adjustable voltage regulator (DC-DC step-down, LM2596) attached to each LED to ensure the right voltage supply. The LEDs were evenly distributed on the surface of the heat sink to ensure a proper lighting quality treatment above the canopy

The main wiring technique remains the same regardless of the number of LEDs. If you decide to add more LEDs to increase the power output (total PPFD) or add another array of LEDs (a new spectrum/color), use similar wiring technique - just adjust the DC regulator to the proper voltage

*If you connected the LEDs in series, add the sum of voltages together, and set it to the DC regulator accordingly (max. 12V for this particular DC-DC converter)

Light Controller | Arduino Code

If the purpose of your setup is to switch the LEDs On / OFF, then you don't actually need an arduino & the MOSFET. By plugging the power supply into the wall, you control the entire LED panel

If you want to have full control over each LED array, precisely dim separate channels, switch it ON / OFF remotely, or according to a defined timer, simulate the sunrise / sunset, etc. then follow the next instructions!

In my setup, the LED panels together with other sensors and actuators for the whole hydroponic system, were controlled using Arduino MKR1000. The software was based on the open source “LightController” library, which is a 24 hour light scheduler designed to provide easy support for moonlight, sunrise/sunset, siesta etc., and modified to suit the purpose of my experiments.

The software allows to define the number of channels associated with the number of LEDs (one channel per LED or LED array), schedule the time, select the fading mode, and set the analog value (from 0 to 255) to linearly or exponentially increase or decrease the intensity of the LED during a defined interval of time.

The software is constantly checking the actual time from the real time clock module (RTC DS3231, AT24C32) connected to Arduino, and if the real time matches with the scheduled time defined in the code, it triggers the PWM pin and starts increasing or decreasing the analog value, to which the LED responds in change of intensity.

Hydroponic Setup | Seed Starting

The seeds of leafy lettuce (Lactuca sativa L. ‘Pflück Lettuce’, DE) were sown in paper towels and placed inside a germination tray (13cm x 18cm x 6cm). The tray was hydrated with tap water until saturated. The seedlings were grown at 23°C (± 0.7°C) and the relative humidity of 90% (± 3%) measured every 15min by a digital Humidity and Temperature Sensor (AM2301, DHT21 sensor, DE)

After 10 days, when the lettuce plants developed a small first true leaf, the seedlings were transplanted into growth chambers set up within a deep flow technique (DFT) hydroponics culture system. A nutrient solution consisting of 5N–3P–8K fertilizer (IKEA VÄXER Fertiliser, DE) was held in a 10L reservoir

The solution was aerated constantly with a 5cm-diameter air stone ball attached to a 240L/h air pump. Plants were placed in 2.5 cm diameter holes cut into the top of the DFT troughs, making sure that 1.5 – 2cm of the bottom of the growing medium is submerged.

After one week, the lettuce was transplanted in a bigger system with similar parameters

Nothing new here, classic garage hydroponics!))

Results

Awesomee aaa? four weeks progress!

When you've spent so much time on growing your own lettuce, it just cannot compete with the one from the supermarket. Eating fresh lettuce leaf on a morning sandwich - F*uckin' delicious!

Yes, I know that this LED panel looks frankenstein'ish! But think of it as a very raw functional prototype

Overall, I was really satisfied with the performance of the LED panel. However, in my next assembly I would add some white LEDs to be the main lighting source, and additionally the rest of colors to complete the spectrum.

Some additional improvements would be to solder everything directly on a PCB, and basically package it a bit nicer to give a final product look. Task for the future, keep updated ;)

The ideal 'light recipe' is still a complex topic, but doing research, customizing and trying different combinations at home, gives a pleasant feeling of being a part of something really big!

Final Note

Where did your #food come from? How good is it for you?

These questions require so much information, all because we've designed the system maybe not for the best goal: More Cheap Food, but not the goal of nutrition, or environmental stewardship

When you take a certain set of genetics and put it inside of a certain phenome, or "climate", it will express something. That's called the phenotype. We want to understand under what conditions do those genetics express flavor, nutrition, size, color.. so we design environmental factors like CO2, temperature, humidity, light spectrum, light intensity, and minerality of the water to increase yields, reduce production time, and influence the taste, appearance, and nutritional content of plants

The goal is to build a base of knowledge for #MachineLearning & #AI, and generate a shared language of "digital climate recipes" for indoor farming, that can be shared across all the continents using open-source technologies. I believe that the next revolution in agriculture has to be based on open science

What's really cool is we're learning about genetic difference between human to human, and that's providing so much insight into what you should eat, versus what I should eat, or what someone else should eat.

Imagine growing something very specific to you?!

CONGRATULATIONS - YOU'VE MADE IT

If you reached so far, you must be really stubborn my friend :D

Hope that you enjoyed going through this tutorial, learned something new, and had fun reading this :)

I encourage you to challenge & doubt everything I wrote here, think of new innovative ways to approach the same problem, and TAKE ACTION!

Who, If not us?

Best,

Dmitrii ALBOT

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