A cheaper way to measure PAR than a regular PAR meter, you can use the SQ-120 with a multi/volt-meter and with an easy conversion translate that figure to PAR. To use the SQ-120 you will need a voltmeter that can read mV (milli-volts). Connect the positive lead of the voltmeter to the white wire of the SQ-120 and the negative lead of the voltmeter to the black wire of the SQ-120. Once you are reading the mV output from the sensor, simply multiply that reading by 5.0 to get your PAR reading.
From the manufacturer:
The SQ-120 is a self-powered, analog original quantum sensor with a 0 to 800 mV output that has been calibrated for use with electric lights. The sensor features a rugged, self-cleaning sensor housing design. Typical applications include PPFD (Photosynthetic Photon Flux Density) measurement over plant canopies in outdoor environments, greenhouses, and growth chambers, and reflected or under-canopy (transmitted) PPFD measurements in the same environments. Quantum sensors are also used to measure PAR (Photosynthetically Active Radiation)/PPFD in aquatic environments, including salt water aquariums where corals are grown. Sensor includes IP68 marine-grade stainless-steel cable connector 30 cm from head to simplify sensor removal and replacement for maintenance and recalibration.