Pulsed LED multi-wavelength illumination

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    Mark Ciotola

    Plants need several different wavelengths in which to thrive. Red light simulates the Sun (which is actually predominant in the redder and IR wavelengths) and drives photosynthesis. Blue light simulated the background sky and signals to plants which way is up, for purposes of root and stem growth. One way to solve this is to include light emitting diodes (LEDs) of different wavelengths, which is an approach seen in many plant chambers (red and blue LED’s for a combined purplish sort of light). Unfortunately, different types of LEDs have different current-voltage (IV) characteristics making them inefficient to combine.

    There is a rumour out of University of Florida that pulsed LED light is as good as steady LED light, but at a significant energy savings. This also solves the problem of different IV characteristics for that different LEDs. So I am alternately pulsing red versus blue LEDs in a 1U plant growth experiment cube. See linked video (warning: flashing lights): https://www.spacegrowers.org/cube_red_blue_pulse_002_r/

    I am using an Arduino for convenience, but other controllers could be used, perhaps even a 555 timer chip. (By the way, this set-up is just to illuminate the top 1/3 of a petri dish growth chamber.) As you can tell, the light is rather harsh on human eyes. I will run a few experiments to see if the Florida folks are correct about the plants not minding.

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