Plants absorption of light and the link to CO2 concentrations

It is well known that CO2 levels can be varied well above ambient levels with increases in plant growth. Contrary to popular thought, university studies have documented benefits in CO2 enrichment above 20,000ppm. Yes that’s twenty-thousand PPM. (Warning! Co2 concentrations above 3000 for extended periods can cause headaches in humans and above 5000 can be lethal. So keep it under 3000 at all times.)

But it is commonly thought that lighting levels have a fixed limit, roughly that of high noon sunlight or 10,000 lumens or around 2000 µmol / m2 / s.

But the following graph found on Plants in Action, a web site produced by an Australian university suggests something very different.

To simplify, the far right of the Photon Irradiance scale or 2000 µmol / m2 / s is roughly high noon sunlight.

The three lines are at roughly 150ppm, 350 and 1000 CO2 levels respectively.

The vertical scale is actual absorption of CO2 by the plant, which is directly proportional to actual plant growth.

The interesting thing to note is that at 1000 ppm CO2, the line is still rising up and has not flattened off like it did on the lower 2 lines. That means that plant growth is still increasing at light levels ABOVE that of noon sun, when CO2 enrichment is above 1000ppm.

It’s too bad the graphs don’t continue on for higher CO2 and light levels, but it can be inferred from this graph that at much higher levels, say 2000ppm CO2, one might be able to using lighting levels as high as 3000 µmol / m2 / s .

But this is very important information, because while electricity tends to be the most expensive aspect of an indoor grow, the next most costly is the real estate itself, and more yield per sq foot of floor space can be a big bonus for certain space challenged grows. Especially with LED’s where extremely high light levels can be achieved without the issues of excessive Heat / InfraRed.

I will be performing some tests of this in the future and I welcome anyone who has experience with running light levels significantly above that of the sun.

To those who grow we salute you!


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