naoki
Well-Known Member
Ray & Tyrone, yes, although PPFD of PAR is closer to what plants want than lux/footcandle, and we use PPFD in publication of horticultural (and plant) science, it is not perfect as you mentioned. If the emission spectra are known, Yield Photon Flux (YPF) can be calculated, and it incorporates the action spectrum of plants (i.e. red light is more useful for photosynthesis than blue). Even with YPF, it is not a complete predictor of plant growth (Fig. 8a of the poster below).
This poster is an easy demonstration, and there are lots of things we can learn from it:
http://cpl.usu.edu/files/publications/poster/pub__2576523.pdf
There are several reasons. Action spectrum of plant photosynthesis is calculated under monochromatic light (measure PS rate with a light with narrow range of wave length). So it doesn't quite match with photosynthetic rates when light with several different wave lengths coexists (e.g. white LEDs). One example is the usefulness of green light depends on the intensity of light (when there are lots of red and blue light, the usefulness of green light increases, Fig. 8b). Also different spectra influence the photomorphogenesis (e.g. blue light makes more compact leaves, reduces stem elongation etc, top fig. of Fig. 7 and Fig 8), which is not reflected by PPF or YPF.
Although PPF is not a perfect measure, but it is pretty decent estimate of "usefulness" of light. Take a look at the bottom fig of Fig. 7. 4 blue diamonds (500 micromol/m^2/s) have higher dry biomass than 4 red squares (200 micromol/m^2/s) regardless of proportion of blue light. More PPF gave more growth in this case (obviously the relationship between PPF and growth isn't linear). The proportion of blue light changes almost no blue to mostly blue, and yes, red light (less blue) gives more overall growth, but the effect is not as dramatic as what you expect in terms of total dry mass. So from my measurement, since 3000K and 5000K COB LED showed similar PAR, I guess that neutral to warmer LED would be the sweet spot. But the shape of plants could be somewhat different.
Ideally, it would be nice to do the experiment similar to the lettuce with several species of orchids, but it would take much longer than with lettuce!
Alla, XHP isn't available yet.
Tyrone, yes, I didn't know about the Apogee issue until DavidCampen pointed it out. Percival Growth Chamber comes with a Apogee sensor, but they may have been calibrated for florescent light which is used in the chamber. There are several sensors with nice spectral response other than Li-Cor (which is commonly used among scientists).
http://www.apogeeinstruments.com/content/Quantum Sensors-LEDs.pdf
But all (except Apogee) is expensive. Mine is an old Li-Cor. Even Li-Cor has the problem with sensor shift (blue response become weaker).
http://cpl.usu.edu/files/publications/factsheet/pub__6622553.pdf
So they need to be calibrated periodically (and you have to specifically mention blue shift calibration). Calibration costs almost $200, so I haven't calibrated mine yet.
For those, who are interested in this kind of topic, I put bunch of related link to this thread, which I should update at some point.
Similarly, there is a HUGE variation in the spectral sensitivity of consumer level lux/footcandle light meter. So values from one meter may not be comparable values from another meter. But they are still useful to give some rough idea.
This poster is an easy demonstration, and there are lots of things we can learn from it:
http://cpl.usu.edu/files/publications/poster/pub__2576523.pdf
There are several reasons. Action spectrum of plant photosynthesis is calculated under monochromatic light (measure PS rate with a light with narrow range of wave length). So it doesn't quite match with photosynthetic rates when light with several different wave lengths coexists (e.g. white LEDs). One example is the usefulness of green light depends on the intensity of light (when there are lots of red and blue light, the usefulness of green light increases, Fig. 8b). Also different spectra influence the photomorphogenesis (e.g. blue light makes more compact leaves, reduces stem elongation etc, top fig. of Fig. 7 and Fig 8), which is not reflected by PPF or YPF.
Although PPF is not a perfect measure, but it is pretty decent estimate of "usefulness" of light. Take a look at the bottom fig of Fig. 7. 4 blue diamonds (500 micromol/m^2/s) have higher dry biomass than 4 red squares (200 micromol/m^2/s) regardless of proportion of blue light. More PPF gave more growth in this case (obviously the relationship between PPF and growth isn't linear). The proportion of blue light changes almost no blue to mostly blue, and yes, red light (less blue) gives more overall growth, but the effect is not as dramatic as what you expect in terms of total dry mass. So from my measurement, since 3000K and 5000K COB LED showed similar PAR, I guess that neutral to warmer LED would be the sweet spot. But the shape of plants could be somewhat different.
Ideally, it would be nice to do the experiment similar to the lettuce with several species of orchids, but it would take much longer than with lettuce!
Alla, XHP isn't available yet.
Tyrone, yes, I didn't know about the Apogee issue until DavidCampen pointed it out. Percival Growth Chamber comes with a Apogee sensor, but they may have been calibrated for florescent light which is used in the chamber. There are several sensors with nice spectral response other than Li-Cor (which is commonly used among scientists).
http://www.apogeeinstruments.com/content/Quantum Sensors-LEDs.pdf
But all (except Apogee) is expensive. Mine is an old Li-Cor. Even Li-Cor has the problem with sensor shift (blue response become weaker).
http://cpl.usu.edu/files/publications/factsheet/pub__6622553.pdf
So they need to be calibrated periodically (and you have to specifically mention blue shift calibration). Calibration costs almost $200, so I haven't calibrated mine yet.
For those, who are interested in this kind of topic, I put bunch of related link to this thread, which I should update at some point.
Similarly, there is a HUGE variation in the spectral sensitivity of consumer level lux/footcandle light meter. So values from one meter may not be comparable values from another meter. But they are still useful to give some rough idea.
oke:
