Dear Lorenza,

Are your 900 µmol in the PAR ?

The 900 µmol is the average solar radiation in my city, after conversion from W/m2. And my photobioreactor is equipped with cool white LEDs.

Dear Lorenza,

I checked with personnal data, your value is not too high, in July in France I found 722 µmol, in the littérature you can find maximum values about 2000 µmol; Your question is very interesting by the confrontation  for an environmental parameter between in situ and in vitro conditions, with agitated culture you can decrease the average light irradiance received by your algae by increasing your initial cell density and/ or by increasing the size of your photobioreactor however, your cells even a very short time, will be submitted to 200-300 µmol, so I think that the agitation regime slow/ fast could be an important parameter concerning photo-inhibition.

A priori,  non agitated batch culture will support the lowest light irradiance.

I am waiting answers by photobioreactor designer.

Bien cordialement

Claude

I am using this photobioreactor, in which the led lights are sitting just behind the tubes, so the light source is very close to the cultures:

http://www.psi.cz/products/photobioreactors/multi-cultivator-mc-1000

That's why I think I cannot supply 900 uE for 18 hours. They will be photodamaged in a while, I guess. So, I am still wondering how to plan a good simulation in the lab.

L.

Well, I would say it also depends very much on the species you are about to grow. We routinely use 500 uE (or even higher) for algae in light/dark cycles or in continuous light. In fact what you see is not photoinhibition but a major growth improvement. We are using the same bioreactor like you. 

Dear Lorenza, I had the same question for some of our tests. I have read that below 400 mE you don t have sufficient light to start the photosynthetic process, and that above 2000 mE there is photoinihibition and cell death. If your source is planar, like say sun over ocean, then agitation can reduce direct exposure time and share the 2000 mE amongst a number of cells, but then you must calculate the hydrodynamic stress and rates for the shuffling as excessive shear-stress in some strains might cause cell death. Hope it helps still, if you have results of your quest that you can share, then I am interested.

PS: this raises another question: what do you think of the theory of alternance between periods of illumination and period of darkness on the growth of algae? since you are in an environment where light is present 18 hours a day that theory could have an influence on your results, or your results might bring some additional light (pun intended of course) to that theory.