COB LED hybrid DIY build.

Blue (430~485nm): Blue LEDs are really efficient at producing photons. In fact virtually all "white" LEDs are simply a blue LED with a phosphor coating. However just like with UV photons, plants have to down-convert blue photons to a lower (red) energy level to use them in photosynthesis - wasted heat energy. Blue photons do have one very important feature though, and that is they inhibit auxin synthesis. Auxin is a plant hormone that causes elongation, so if you don't want stretchy plants, some blue wavelength light is a must. An important caveat is that auxin and its blue-wavelength-reactive buddies are important for flowering, which is why it makes sense for people switch to a "warmer" color spectrum during flower. The increase in auxin and the decrease in light from switching to 12/12 both explain why a plant grows 2X to 3X in height during the first few weeks of flower.

Green (500~565nm): There's this HUGE misconception, based on chlorophyll absorption charts, that somehow plants only need red and blue photons to grow. There are two problems with this. The first problem is that it assumes the only light-dependent activity in a plant is photosynthesis, which is flat out false. The second problem is that those charts of chlorophyll absorption assume you've isolated a choloroplast out of a leaf, or even isolated cholorophyll molecules in solution. What happens in a leaf - a complex, three dimensional structure - is much more interesting. Here's a fantastic article that explains that green photons are actually MORE efficient than red at driving photosynthesis. It's well worth the read. The problem with green LEDs is they are very inefficient at producing photons. A typical well-designed green LED will produce 50 lumens/watt, while a red from the same manufacturer with similar specs will produce the same lumens for 75% the power. In fact, some white LEDs produce more green photons per watt than green LEDs. Go figure.

Red (620-660nm): It's your main photosynthesis driver, duh. PSI and PSII photosynthesis pathways require two photons, one 680nm and one 700nm. Red LEDs typically come in a nanometer peak around 620-630, which means you don't have to waste much photon energy as heat in order to get usable photosynthesis energy. The only downside of red LEDs is they cost more (than whites) if you are building a DIY setup. Red LEDs are pretty rad because they run at a much lower voltage than white/blue/green/odd color, so for ~12V and 1 amp, you can often run 5 red 3W LEDs in series where you'd only be able to wire 3 white 3W LEDs in series. You can grow monster plants with setups that utilize only red LEDs with a little white thrown in to cover the rest of the spectrum.

White (100% PAR): I'm not going to bore you with explaining the in's and out's of color temperature or that cool white = veg, warm white = flower. You can read all about that in a million posts in this sub. A white LED is just a blue chip with a phosphor coating. The coating converts blues into a chemically-controlled spectrum of photons across the entire visible spectrum. "Warm white" LEDs have a short 460 blue peak and a broad slope from green to red. "Cool white" LEDs have a tall 460nm blue peak and a very similar slope from green to red.

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