Cheap PAR meter hack - Use a Lux meter to measure PAR accurately

I test four cheap Lux meters from Amazon to see if they can be used to measure PAR (Photosynthetically Active Radiation) so you can use them to optimise your grow light setup. The measurements are compared to the benchmark quantum sensor for measuring PAR from Apogee which costs about $500. The results are surprisingly accurate.

The Lux meters were tested with the two most common spectrum in LED grow lights sold in the last few years, a 3500K or neutral white LED and a White LED with added red LEDs. Other grow light spectrum were not tested and thus hack will not work for HID or 'Blurple' led grow lights (with blue and red diodes only).

Each Lux meter reading was graphed against the benchmark quantum sensor readings. On the top of each chart is the factor to apply for each Lux meter to convert the lux readout to PAR in µmols/m²/sec.

For example if you are using the UNI-T lux meter and you have a white and red LED grow light you multiply the LUX readout by 0.017 for the PAR equivalent.