How to calculate or measure the plane of angel for the light provided to a microalgae culture in photobioreactor?
In an experiment for the cultivation of microalgae a photobioreactor was designed with LED lights for the provision of light energy. The specifications of LED Lights are given as; wattage of 8 W, Beam angle 140◦, 560 lumen (Lm), power of current 69± 5 mA, color of light 6500K, frequency 50Hz.
Now the questions are;
1) How 140 deg is numerically equivalent to 40 deg?
2) What is meant by “planes” the angle is measured? And how it could be given least value?
I guess that the 140 deg is meant to be the specification of each LED. When you have a LED panel comprised of several LEDs this value does not have much meaning, as the lights of the individual LEDS overlap and sum up. You need to have the light intensity (in lumen or lux, preferentially to be converted to micromol/m2/s) of the whole panel from the relevant distance of the vessel from the panel. In principle if you have an infinitely large panel, you can calculate this value using the 140 degree solid-angle, though. But it is easier to measure. :)
Where do you get the "40 deg" from? it is not in the specification.
Another problem is that it is difficult to convert the light intensity given in lux with color temperature to photosynthetically active photon number per area. It makes hard to compare results of different photoreactors, although the results in one type can be perfectly consistent.
Thanks a lot for your informative suggestions. it is really helpful for me. w.r.t 40 deg, I have submitted an article in a journal for publication. In its review from the reviewer got this sentence as comment "140 deg is numerically equivalent to 40 deg. It should be mentioned between what planes the angle is measured or the smaller angle is to be given in the manuscript". Therefore I was uncertain to understand the asked question.
I can not imagine any contexts or cases when 140 degree would be equivalent to 40 degree. I do not have an idea what the referee meant to say with that.
Another thing is that if I were you ( I would perhaps leave the specification of the individual LEDs in the manuscript or remove them, but ) definitely I would specify the final light source as one whole unit. I still guess that you created a light panel for the photobioreactor by combining several LEDs in a certain geometry. The main important things are the light intensity (eventually this is the number of photons) at the surface of the vessel and the wavelength distribution of those photons (using either spectral graph or colour temperature in your case). And of course the width or depth of the vessel or culture layer, which also has fundamental impact on the availability of photosynthetically active radiation that each cell can encounter in average.
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