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During normal operation it would be nice for the average individual to be able to measure the efficiency of the process and "tweak things" so to speak. In this light a simple approach might be appropriate. The LED's puts out light. When algae grows it absorbs the light and gets bigger or more of it, blocking out the transmitted light. So why not put a photo cell (light to electricity conversion) on the other side of the tank. Measure current output as an indication of the amount of light getting through the algae. By plotting or measuring rate of light attenuation this should be related inversely to biomass growth rate. The amount of change over time (decrease in light) would indicate the relative efficiency of the growth, and tweaking can be done to maximize growth.

Now thinking later on - perhaps this idea could be used to automatically monitor and control some portion of the process say control amount of nutrients, when to harvest the crop etc.


The only problem with that approach is that the rate of light absorption doesn't really have a linear relationship to the rate of photosynthesis. You can, for instance, simply increase the light intensity and more light would be absorbed right? What you could end up with is shutting down photosynthesis altogether, because the cells chemical process will shift from photosynthesis to a mode of protecting the cell from damage. The same goes for nutrient concentration, too mutch CO2 or the pH way off and you get the same result. If there is a limiting nutrient also, it will not matter how much light is being absorbed, the rate of photosythesis will not follow. The most direct way of measuring the rate of photosynthesis is to measure O2 production.