A Single-Watt Hydroponic Lighting System

Hydroponic systems are an increasingly popular way to grow plants indoors using a minimum of resources. Even some commercial farming operations are coming online using hydroponic growing techniques, as these methods consume much less water, land area, and other resources than traditional agricultural methods. The downside is that the required lighting systems often take an incredible amount of energy. That’s why [ColdDayApril] set up a challenge to grow a plant hydroponically using no more than a single watt.

The system is set up to grow a single pepper plant in what is known as a deep-water culture, where the plant is suspended in a nutrient solution which has everything it needs to grow. The lightning system is based around the Samsung LM301B which comes close to the physical limits for converting electricity into white light and can manage around 220 lumens. A special power supply is needed for these low-power diodes, and the light is efficiently directed towards the plant using a purpose-built reflective housing. By placing this assembly very close to the plant and adjusting it as it grows, [ColdDayApril] was able to take the pepper plant from seed to flowering in 92 days.

It’s worth noting that the rest of the system uses a little bit of energy too. A two watt fan helps circulate some air in the hydroponic enclosure, and deep-water systems usually require an air pump to oxygenate the water which uses another two watts. This is still an impressive accomplishment as most hobbyist builds use lighting systems rated in the hundreds of watts and use orders of magnitude more energy. But, if you’re willing to add some fish into the system you can mitigate some of the energy requirements needed for managing the water system even further.

24 thoughts on “A Single-Watt Hydroponic Lighting System

  1. Very neat, now just need the light to get further away from plant automatically based on the plants weight perhaps (so it can be a simple mechanical linkage) just to make it really easy.

    A slightly wider setup would also make big overall system gains as the fan and pump power probably wouldn’t need any increase to handle some more plants, I’m far from an expert but I’d think that same setup could easily scale up just adding more bulbs for each plant.

    1. A “float” switch with a net paddle over the plant to turn a motor on and off. Once the plant touches the net and lifts it up slightly, the motor gets turned on for a few seconds.

    1. Went to the link and was very surprised to see ” Red/Blue LEDs would be even more efficient in theory, as the chlorophyll has two absorption peaks near 460nm and 660nm. But I have seen mixed results online. In most experiments I’ve seen, the white lights outperformed the red/blue ones using comparable amounts of energy.”

      1. Plants are almost never energy limited – growth is limited by CO2/water uptake. So the key to get the best growth is to trigger the right signals to encourage growth, not to provide them buckets of energy. And plants use the other wavelengths of light basically as “sense” to direct growth.

    2. From a quick (and amateur) look at the datasheet for the leds chosen I would think that the peak output appears to be at 450nm and at 600nm, and thus I suspect covers both red and blue light requirements.

    3. There´s more than chlorophyll when it comes to photo-absorbing pigments that play a role in plants grow.
      Never wondered why autumn leaves display such yellow, red or even violet colors ?
      Short answer is: when the leaves die, chlorophyll is the first pigment to degrade. Their resulting color is the mix of the other pigments: carotenoids, anthocyanins, flavonoids, betalains.

      1. Bingo! You have various other reactions going on which use other wavelengths. The whole red/blue thing is massively misinterpreted but when used correctly used you can use it to steer a plant into certain growth patterns or force them to flower on demand

      2. Personal experience growing super hot chilis with hydro buckets on my balcony. Flowering is not at all same as fruit. You need bees or other pollinators unless maybe you paintbrush the pollen around. They also survive multiple years if you bring them in and prune them into dormancy. One winter I figured I’d keep them growing under an LED lamp and with all the reflected light, the stalks and stems all grew leaves too. It was weird. I also got some fruit purely under the lamp but had to shake the plants to get the pollen to distribute. Was nowhere near the ridiculous bumper crop that happened outdoors when the bees were at it. I got like 1-2 gallon bags of dried ghost peppers per plant the last year before I had to move and threw them away. It was like losing a pet.

    4. Look up migro on YT. He goes into depth on lighting colors and what they do for a plant. Green light surprising is used by the plants and is good at penetrating the top canopy to get to leaves lower down on the plant.

  2. With a white led, plenty of energy gets wasted in the spectrum where photosynthesis does not occur (e.g. green). A combination of blue and red diodes targeted at the center of the photosynthetically active wavelengths would greatly improve the efficiency.

    1. Theoretically yes, but there’s interesting studies which show that plants often grow better under white light than under red-blue lamps. It seems that the remaining parts of the spectrum are still important, despite not being absorbed as well.

      I hypothesise that the most efficient lamp is probably some combination of the two techniques, with red and blue providing the majority of the illumination and a smaller white component to fill out the spectrum.

  3. To all comments about red-blue light: you’re wrong and have been scientifically proven wrong. Plants want WHITE light, not blue-red. It’s not all about absorption spectra for chlorophyll. A little dip in green can be tolerated, but blue-red only is no good, see below about greenhouse and sun. But “special grow lights” sells so that’s why grow light vendors love it.

    Red lights are beneficial due to power efficiency (about 10%, not much for the home grower, but much in a large greenhouse). BUT, they need to be used together with sunlight as a supplement. Only red light is no good. In theory blue can be more efficient, but in practice red is used because it is cheaper to manufacture in bulk to the same standard. As manufacturing becomes better and electricity prices go up we might see a shift to blue.

    I’m no expert but I believe cannabis likes far-red (close to IR) lights for flowering, that’s why there is a lot of interest in those. A lot of money in that business so that’s why plant light manufacturers focus on marketing that.

    1. It’s just triggering the right biology. There are specific horticultural LEDs that exist to directly trigger the right responses, but even then, if you’re trying to get the best growth, you’ve got to know the right ratios and timing for it.

      The far-red stuff is true for lots of flowering plants, it’s how they detect the length of day: there’s a phytochrome which essentially acts like an RC, “charging” during the day (Pr->Pfr) and “discharging” at night (Pfr->Pr).

  4. Based on the best known efficacy of ‘White’ LEDS, the highest photon flux on 1 W input is around 3 umol/s. If all of the light produced was emitted over a 10×10 cm square, the PPFD would be 300 umol per meter squared per second, which is about what you’d need to keep a pepper leaf decently photosynthetically ‘happy’. But one W of electricity providing sufficient lighting for an entire plant…. no freaking way!

  5. A single watt and close to the plant . We use a 35 wat led and grow 70 plants under this LED . yes we grow Peppers and Strawberry plants. The secret is the way we use the led it actually replicates the sun 100%

  6. Some design constraints have been inherited from the fusion reactor millions of kilometres away.
    Why only light from the top? What happens when Leds are interspersed like Xmas tree lights throughout the installation? Optimal leaf performance without one shading another?

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