Light analysis

Hi everyone! I measured the photosynthesis performance of one of my Paph plants (philippinense x praestans) under different light tubes. The experiment setup:



A sealed glass box contains the plant and a CO2 meter. The collected data are sent to a data collector program on the computer. The CO2 is measured and one data set is saved per minute.
The idea is easy: The plant uses the light emitted from the light tubes to convert the light energy into usable chemical energy (produce sugar). The plant needs CO2 to do so and lets 02 go, so the air inside the box will contain fewer and fewer CO2 while the amount of 02 rises. The faster this happens the more efficient the photosynthesis is under those light conditions.



The curve above showing the result of a five hour experiment with standard daylight tubes. The plant reacts after 15 minutes after turning the lights on and starts doing photosynthesis. The CO2 concentration decreases very fast at the beginning, but it gets more and more hard for the plant to get the CO2 when the concentration gets very low, so the curve begins to flatten at the end.

I tried different light tubes, to find out which ones will be the best. I tried normal daylight, blue light (normally used in reef aquariums) and the well known purple plant light. Take a look at the curves:



The purple plant light was the most efficient of these three. The light spectrum of these light tubes is perfect for the plants, because they emit red and blue light at the absorption maximum of chlorophyll.
Many people doubt the efficiency of the Fluora tubes from Osram, but for my Paph plant is was clearly the best tube, followed by the blue light tube emitting a maximum at 440nm.
I repeated the experiment with T5 tubes (2 x 80W) and the blue light was better than the daylight tube again. I do not have purple tubes at the moment, but I will try those in the future (Fuji Purple T5). I guess they will be the most efficient again (check the emission curve).



I changed my lighting system some months ago and I noticed a much imporved growth on all my plants. At the moment I use T5 80W tubes 50% of the blue type and 50% of the daylight type. I will buy the Fuji Purple T5's and use them for 50%, blue 25% and daylight 25%. The problem is that those T5 purple light tubes are pretty expensive here in Switzerland

Sounds quite interesting!

This is a very cool experiment Polyantha!

Can you account for (standardize) for total intensity or lumen output for the different bulbs?


And temperature/humidity was the same on all runs? With 5 hour runs I would suspect that the individual runs were done on different days, and other conditions effecting metabolic rates could change.

But those slope/rates on the different bulb runs are definitely significant.

The intensity of the light bulb was not an important criterion for me, since I wanted to find out which one is the most efficient (18W per bulb). So I don't have to take the Intensity into account. (Hope this is what you meant Rick)

The runs were made on different days, same time every run. The temperature, humidity and CO2 were the same every run (plusminus 1°C, plusminus 3%). The humidity in the box changed significantly during the test, at the end it was over 95% every time. But this will not change the result, because every run the humidity increased the same way and with the same speed.

polyantha said:

The intensity of the light bulb was not an important criterion for me, since I wanted to find out which one is the most efficient (18W per bulb). So I don't have to take the Intensity into account. (Hope this is what you meant Rick)

But this will not change the result, because every run the humidity increased the same way and with the same speed.

Click to expand...

Very good standardization of input data. This is very cool Polyantha!!

In the second experiment I do not see much difference between the blue and daylight. Both plots look to have the same slope, if you shift the blue line to the right by about 15 minutes it should very closely superimpose on the white line.

I like this experiment!

But under these light levels does it really matter?

You will build up a proton gradient over the thylakoid membrane very fast, and that will stop photosynthesis.

At that point it will be the light independent ATP synthase that is the limited factor (leveling out the proton gradient), though ATP synthase is much slower under this condition. Looking at your graphs you hit this limit within about 10 minutes with all light sources, the steady state constant level of CO2. This proton gradient is not dependent on the CO2 level at high light fluxes and adding more CO2 will not solve this problem.

My interpretation is that your light levels are way to high to make the ATP synthase keep up with Photosynthesis and you are wasting a lot of energy in excess light (and heat production).

Magnus, it sounds like that you are describing the photo-saturation. But how can you tell it without photosynthesis-irradiance (PI) curve? I know a bit about open-system IRGA, but I'm not familiar with the closed system like Polyantha's.

Polyantha, what kind of CO2 sensor did you use?

DavidCampen said:

In the second experiment I do not see much difference between the blue and daylight. Both plots look to have the same slope, if you shift the blue line to the right by about 15 minutes it should very closely superimpose on the white line.

Click to expand...

Yes David I think you are right with that. Only a small difference, since the slope of the curve shows how much CO2 was used per time.

Magnus A said:

My interpretation is that your light levels are way to high to make the ATP synthase keep up with Photosynthesis and you are wasting a lot of energy in excess light (and heat production).

Click to expand...

How can you make an interpretation about light levels without knowing the distance between the light tubes and the plant?

naoki said:

Polyantha, what kind of CO2 sensor did you use?

Click to expand...

I used the ZyAura Datalogger for CO2, rel. humidity and temperature:

https://www.distrelec.ch/datenlogger-co-2-luftfeuchtigkeit-temperatur/zyaura/zg1683ru/910054

One of the cheapest on the market. I checked the data with a 4000 Dollar CO2 meter in the lab of my school and I can tell you that its working fine. A true bargain for only 160 Dollars.

This is great Polyantha. While I agree that your testing was sufficient for finding out simply "which is better for you", expanding on some earlier posts, it would be nice to know both the spectra and light intensities involved - they are commingled in this testing.

Did someone test the new generation of LED which are used to replace normla halogen lamps.

A friend who works in the Aquatic industrie told me after I asked for the best light to replace my HQI once, that I should try this once. The where very cheap.
No idea about the spectrum, but my plants reacted with stronger growth. and both new once only need 7 times lower energy, I will try it for my orchids too in future. Would be interesting to test this one on this system too.
If you want you can have one for free from me if you share the results with us

Ray said:

This is great Polyantha. While I agree that your testing was sufficient for finding out simply "which is better for you", expanding on some earlier posts, it would be nice to know both the spectra and light intensities involved - they are commingled in this testing.

Click to expand...

spectrum of Osram 865 T8:



spectrum of ATI Blue Plus T5:



spectrum of Osram T8 colour 67:



spectrum of Osram Fluora:



I could make another testing with the light intensities all the same (changing the distance to the plant to get a constant intensity, right? Is that what you meant Ray?)

Dido said:

Did someone test the new generation of LED which are used to replace normla halogen lamps.

A friend who works in the Aquatic industrie told me after I asked for the best light to replace my HQI once, that I should try this once. The where very cheap.
No idea about the spectrum, but my plants reacted with stronger growth. and both new once only need 7 times lower energy, I will try it for my orchids too in future. Would be interesting to test this one on this system too.
If you want you can have one for free from me if you share the results with us

Click to expand...

If I do not know the exact spectrum of the lamp it would not be worth trying I think. If you know the model number we could find it out tough. Is it white colour or this purple grow LED colour?

Yesterday I ordered 4 T5 80W tubes:



Should work very well with my plants, there is a peak at 440nm (blue) and one between 650-660 (red).
Will try the testing with one of those plants:

P. philippinense
P. roth
P. praestans
P. gigantifolium (probably too big for my box )
P. stonei
P. roth x gig (probably too big)
p. randsii

What should I try? What is interesting for you? Opinions?

The test will be done with daylight, blue and the plant light again. And I like Ray´s idea with a constant light intensity. So there will be two tests coming...

Polyantha

Can you do some more runs using one type of bulb, but changing the distance between the plant and the bulb. (Looking at intensity differences rather than optimized spectral quality).

If one is interested in how plants react to different spectra, most people would control for the PPF (micro moles/m^2/s). Here is an example. But controlling for the lux (or fc) is probably more practical for us.

It would be interesting to look at the low light paphs. Ray mentioned that the spectra is probably quite different under the canopy. So those plants may have adapted for different spectra. But I guess most of your plants are relatively high-light Paphs.

One comment about purely blue light (you may already know this). In many plants, the strong blue light reduces the leaf expansion, and makes a compact plants. You can see the effects in the poster linked above (I haven't seen an experiments with orchids, though). So the blue tubes may give ok photosynthetic measure, but it may or may not give desirable results.

Also, if you are measuring again, it would be good to control the hydration level (e.g. measure 1 day after watering etc) for 2 reasons. First, it influences the stomata opening (and gas exchange rate). Second, since the measurement is at the whole plant level (not for each leaf), the respiration of microbes in the pots affect the measurement. The hydration level will influence the microbe activity. I don't know how strong this effect is for coarse media like bark, though.

Thanks for the info about the cheap CO2 sensor!

Hehe....everybody jokes on me when I take a pic with purple background, and I always tell that it is because my lightening Osram Fluora tubes!!!!!

Rick said:

Polyantha

Can you do some more runs using one type of bulb, but changing the distance between the plant and the bulb. (Looking at intensity differences rather than optimized spectral quality).

Click to expand...

Oh yes this will be a great test!

this is fascinating - even though I dont understand much of it.
it might very very useful for optimising lighting conditions for you paphs do you dont waste energy.

Thank-you for this.

Ozpaph said:

this is fascinating - even though I dont understand much of it.

Click to expand...

I try to explain what data I am collecting: In the picture above you can see the reaction called photosynthesis. The plant produces sugar (glucose) from co2 and water. The more sugar the plant produces, the better growth and vitality will be. So if the plant produces more sugar, it will also need more co2. This means that the co2 concentration in the box goes down and the o2 concentration rises. The faster the concentration of co2 goes down, the more sugar is produced per time.
Thats what the curves show at page one: if they are steep, the lamps are efficient.

Thank-you very much for the explanation of photosynthesis - I understand that.
I dont understand the ATP/rate limitation comments.
I assume there must be some rate limiting steps or all plants would grow fast if enough light, water and CO2 was supplied.

Ozpaph said:

Thank-you very much for the explanation of photosynthesis - I understand that.
I dont understand the ATP/rate limitation comments.
I assume there must be some rate limiting steps or all plants would grow fast if enough light, water and CO2 was supplied.

Click to expand...

Yes that arrow that connects from left side of the equation to right side is were all the craziness occurs.

So expanding that simple arrow is not so simple. Especially if you consider that plants produce a lot of other organic chemicals than carbohydrates, which also depend on that tiny fraction of NPKCaMg........

But from a big black box approach there's a a lot to be said for the procedure that Polyantha is running.