Back in our high school biology or in a first year botany class you may have done this very practical experiment with spinach leaves.
Isolation of Chlorophyll from Spinach
If you substitute the cultivar you want to know more about the amount of pigments present.
Why would I want to know what pigments are present in my favorite plants? Well the spectrums you want for LED lighting.
Light that is absorbed by the plant is totally based on pigmentation. We know the absorption of light based on the form of chlorophyll. The ratio of chlorophyll a and chlorophyll b. The absorption spectrum is different for for the two forms of chlorophyll, and well documented. This is where PAR comes from, but is only part of the story.
What is not well documented for cannabis is the absorption of your secondary pigments. But, these secondary pigments are know to be key in the production of secondary plant compounds. And why we want to grow cannabis is the secondary plant compounds, THC and CBD.
Secondary plant pigments are generally the starting point for for secondary plant compounds. You excite the pigments with light just like we excite chlorophyll, with light.
If we know the absorption spectrum of the secondary pigments we should see more secondary plant compounds. (Reference needed here, Look at Erthroxylum coca and Glycine max).
I would start by picking the cultivar you like best. Pick a really fine looking plant, you need one of your best, that is in flower. You only need the leaves.
Use the extraction method I sited above.
Additional equipment needed
A high quality Pyrex flask beaker in the 1000 milliliter size. This beaker is flat on two parallel sides. I like the purists silica glass I can find. They have an absorption spectrum of there own and is documented.
With a really fine quality light and a good spectrometer. Do the following.
See what the light spectrum is of your light.
See what the light spectrum of light is through the empty flask beaker.
See what the light spectrum of the the extraction liquid is prior to extraction.
Now fill the flask with your extraction. Take your your spectrum readings from both the light passing through and light reflecting from the front. The front measurement is harder. To help with the front collection, I use a good quality 10x broad lens to help capture the light for the spectrometer.
The light passing through shows what light is not used by the plant. Light reflecting from the front shows what is not being absorbed but reflected.
With these two pieces of information you can determine the exact spectrum your plants need for optimal growth.
It not just total PAR we care about. We want to know what the total absorption spectrum of the secondary pigments.
Now you know why I want tunable spectrums from my light source and why LED lights are my dream come true.
I have done this very experiment on a lot of floriculture crops. Most particularly in Latherus oderatera cultivars (sweet pea).