Depends I guess but they would likely be the ones that work with LEDs and they will be waterproof too. (at least the probe part). Maybe google PAR meter rental? an example http://growgreenmi.com/rent-a-sun-system-par-meter-w-remote-sensor-weekly-rental-rate Rent a Sun System PAR Meter w/ Remote Sensor - Weekly Rental Rate growgreenmi.com/rent-a-sun-system-par-meter-w-remote-sensor-weekly-rental-rate Rent a Sun System PAR Meter w/ Remote Sensor for only $70/week or $200/month PLUS a $250 deposit. Sun System PAR Meter comes with an integrated sensor to measure photosynthetic active radiation (PAR). Use inside with Sun System grow ligh.