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Do Plants Absorb or Reflect Green Light

Tuesday, 1 November 2016  | 

Ok so there’s a lot of talk online about plants and green light absorption or reflection.

You will see a lot of views on this primarily from white light manufacturers who insist that green is the best light for your plants and will try to mislead you.

So, we have the following statements which re-surface online commonly:

 
Plants can use green light when it if from a high powered white light source!!

Well this is true but it is also very misleading, for example this is a statement often bandied around by white light companies and in no way means that green light is better for your plants. 

So firstly lets define what a white light is right? A white light is just a mixture of all colours in varying amounts until it appears white (cool white, warm white) in some manner to us humans.

It goes without saying that green will also be used when mixed with other mono led colours as this is what white light is made up from.

For example most HPS spectra is primarily green through to orange with little or no blue and very little red 660nm.

If you look at the chart below you will see one of the market leading HPS brands spectral output and it does leave you wondering how the plants grow at all with so little blue?? Well this is because green light helps drive photosynthesis harder so even though a spectrum can have very low amounts of blue and red the photosynthesis is driven harder by the presence of green light.

We include varying amounts of green - orange in most of our lamps as we found in our own testing that final bloom stages without any green and amber resulted in lower quality end yields.

HPS Spectrum
We liken LED grown plants to athletes in training eating an extremely healthy and well balanced diet which results in a healthy and vital individual.  For plants this means higher quality end products and greater oil content. Here we liken it to a person eating junk food for their three meals a day, the person will still be active and mobile and gain a large amount of weight by eating this diet but in no way will the person be healthy or vital and will be deficient in many areas of their health.  For plants this means medium quality end products with a lower oil and vitamin content versus led grown plants grown with a mixture of HPS and LED.
 
Green is best for your plants as the sunlight is primarily green!!

This is also a very misleading statement as if you study plant photobiology you will be well aware that reds and blues are the main driving force in plants energy production and green provides photosynthesis via the carotenoids and stimulates many other plant functions.

Of course plants can be grown under almost any light and the growth profile, yield and quality will reflect the light sources efficacy.

Also if you look at the sun's general spectral output and compare against the McCree absorption curve you will see that much of that green is never used and how much of the remaining green is used will depend on the plant species and growth stage.

 
Plants reflect green light as their leaves are green!!

Well its simple really, plants do both reflect and absorb green light!!

So basically plants use all the colours in the spectrum in different amounts in different ratios depending on the plants current requirements.

To say that plants reflect green is both true and un-true and to pin it down to any one colour is non-sensical as your plants leaves are constantly changing to different shades of green so therefore the green they reflect will be different at different times of the plants life or health states.