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Spectrum visualization tool

A project log for Planty Happy Grow Light

75 Watt LED grow light

t.oster92t.oster92 10/25/2020 at 10:480 Comments

I wrote this python script while designing the lamp. It will calculate the output spectrum and efficiacy of the lamp, and some other things, depending on LED currents. For me, it was most important to get an idea of how well my plants will be able to utilize the light, so i chose to take the 'Yield Photon Flux' (YPF) as a primary measure of how efficient my lamp will be. For most other lamps, in contrast, only the 'Photosynthetic Photon Flux' (PPF) is given, but this won't take into account that a plant will use green light less efficiently than red and blue. 
For the calculation of YPF i used the well-known McCree curve. McCree averaged the response of single leaves of different species, so this curve most likely doesn't tell the whole picture, but it is a good starting point. 

I tried to make my lamp model as accurate as possible, so LED temperatures, forward voltages and current dependant droop are taken into account. 


The tool

You need to have Python 3 installed, and several other common libraries like matplotlib etc., and download light_spectrum.zip in my file section. After unpacking and starting light_spectrum.py, the blue sliders can be shifted with the mouse to change the LED string currents. The spectrum will change accordingly, and efficiacy, power and YPF are calculated from the currents. 


I created models for Lumileds SunPlus20 series, but other LED models could be imported as well. For this, you need to change the csv files in the "CurrentVVoltage", "FluxVCurrent", "FluxVTemp" and "Spectra" folders to match your LED behaviour. You will also need to change the x0r,x0b,x0w factors in the "leds.py" script. They can be calculated with the 3 scripts lumen2powah, powah2lumen and PPF2powah.

This way, you can compare how well different LEDs would do in this application. It won't matter if PPF or lumens are given - these tools will make all LEDs comparable. I used the tool for this purpose.

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