There are a number of smartphone apps which claim to allow you measure PAR (Photosynthetically Active Radiation, the wavelengths of light that grow plants). An accurate quantum sensor for measuring PAR cost over $500, way out of reach of most home growers. I was interested to see if an app can work accurately and enable you to measure the PAR intensity in your grow room and optimise your setup.

I have tested the available Apps from Android and IOS on a Samsung S20 and iPhone 12 to see if they can provide accurate PAR readings. I used the two most common grow light spectrum on the market today – a mid temperature white light at 3500K CT and a light with both mid temperature white LEDs (3500K CT) and added red diodes. I did not test with HPS or Blurple LEDs, they are likely to be inaccurate with those light sources as the spectrums are more complex for the app to interpret.

I measured with the smartphones and compared to the readings from an Apogee SQ500 quantum sensor at PAR intensity levels of 150, 300, 450, 600, 750, 900 and 1,050 µmols/m²/sec.

The first test was with a white LED grow light, 3500K CT

PAR app meter graph white LED

PAR app meter graph white LED

The three Android Apps were inaccurate but the Photone App on IOS was very close right through the range of PAR intensity. As per the instructions the Photone App was used with a piece of 80gms paper over the front camera as a diffuser and the light source selection was set to ‘LED full spectrum’.

The next test was at the same PAR intensity intervals but with a grow light with both mid temperature white LEDs (3500K CT) and added red diodes

PAR app meter graph white +RED

PAR app meter graph white +RED

Again the Android Apps were not reliable but the Photone App on IOS was consistent. The result was lower than the Quantum sensor reading by 10% so you can use this factor to adjust your readings with the app for this grow light spectrum. Again, as per the instructions, the Photone App was used with a piece of 80gms paper over the front camera as a diffuser and the light source selection was set to ‘LED full spectrum’.

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