I’m looking to buy or build a PAR (Photosynthetically active radiation) sensor, but my googling and other searching has come short.
This is basically a light spectrum analyser in the 400-700 nm range, measuring the amount of energy the incoming light has that is useful for photosynthesis if plants. Plants use the light on both ends of the spectrum, but not the middle half.
Sunlight is of course full spectrum and a simple lux meter does the job well there, but LED lights (especially dedicated growing lights) are not, and that’s where the PAR comes in play. The PAR of such lights can easily be 2-3 times that of sunlight with the same brightness when measured with a regular lux meter.
There exist commercial sensors, but those are mighty expensive.
I was thinking maybe a CCD array (as found in cameras - after all they are sensitive to colours) with some software smarts could do the job, but no references to this.
Any ideas on what kind of sensor could do this? What measurement principles can be used? How is it done in commercially available sensors?