Think PPF, not PAR

Specs of the DIY LED light pictured above:
1. PPF measured at the top rim (5 inches below the light):    460 
2. PPF measured on the bottom (17 inches below the light): 290
4. PPF measured in 1 inch from side glass:
    400@the rim; 220@the bottom (very even light spread)
5. Dimmable: to PPF 45@the bottom

Take the moment to clarify a popular planted tank blunder – PAR.

We all have some idea about how much PAR is needed for a low, medium, or high light planted tank. Over the last 10 years or so we have agreed that:

1. Low light is 25-40 PAR
2. Medium light is 40-80 PAR
3. High light is 80-120 PAR

There are 4 important points about the above list. Try to learn them here and now because you won’t find this info anywhere else. Despite that it is super basic. That’s how we are in all aspect of our live – we like things simple so we can go on with our lives. So here it is:

1. PAR is not what makes the plants grow.
PAR are the wavelengths used most by the plants. Meaning – what parts of the light plants like most.

Note: It has been proven that the “peaks”, that plants like are not the only thing they actually need. Plants also need “supporting” wavelengths that do not register as PAR. Hence the use of exotic LEDs that emit UV or far red light. Think of that kind of as you eating pure protein, carbs, fats.  Or eating them with all the condiments, spices, special preparation.  Big difference.

Back to PAR; I can say “I like chocolate, watermelon, and gritz.”. That means just that – a statement what I like. I can not eat my words and get energy. Same with PAR. Plants like certain PAR but can not eat it. You need to provide what they like (the PAR) in certain good amount.

So how much is that “good amount”? Think of me liking what I said I like. Imagine serving me 10 oz of chocolate, 2 lbs of watermelon, and 10 oz of gritz.. NOW I can actually eat!

The same logic applies to plants. Light fixture A emits 10 units of PAR and light fixture B emits 500 units of PAR. Both provide the PAR plants like. But which one will feed your plants better? Clearly the one that emits more of the PAR plants like.

The units that measure how much PAR a light produces are called “PPF” (Photosynthetic Photon Flux). THAT is the measure we need to use when we discuss planted tank lights.

PPF – remember that.

2. The PAR “values” accepted by the planted tank community and listed above are actually super ultra puny

…if you compare them to the marine tanks, growing marijuana, or of course the open sun.

In reality high PPF – 500-1000 – is extremely beneficial for the plants. If your planted tank is hit by the open sun for 30 min a day you will notice a considerable improvement in the plants health and vigor. Of course – that means that the sun light should not be filtered through glass that is colored etc. So the PAR that plants like is what the sun has to give.

3. Even spread
That factor can not be stressed more. You can easily make an LED fixture that is super powerful (ultra high PPF at the correct PAR) but if the light that comes out of it is too directional (using special lenses in front of the LED) what will happen is that you will measure very nice strong PPF when the tank is empty. But as soon as plants start to grow they will shade themselves and other plants. Only the plants that have managed to stay exposed to the too-directional light will survive.

That is why there is no way to get around “light spill” in a planted tank. You WANT the light to bounce inside the glass box. You want it to hit the plants from all directions. You want the light to have both the PAR plants like, the PPF they need to actually eat well, and it all needs to come from all directions. The downside is an area outside – around – the tank that is brightly lit. Without it the tank looks super cool glowing by itself in the dark room, but plants do not grow well in it.

4. None of the above is written in stone.
Depending on what you like, can afford, size of tank, plant species, or want to achieve you can literally use any light you want. People have grown beautiful plants using the old style incadescent bulbs mounted inside shiny tin bread pans, cheapest Chinese strip LED, every kind of fluorescent bulb available, etc. The bottom line is – any light works if it it can emit strong enough light (has enough “umpf”, PPF).

Best link to get more details: