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 red 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 quantum sensor that measures photosynthetically active radiation (PAR) and is calibrated for use with electric lights. The sensor housing design features a fully potted, domed-shaped head making the sensor fully weatherproof and self-cleaning. Photosynthetically active radiation (PAR), or photosynthetic photon flux (PPF), is the wavelength range from 400 to 700 nanometers and is strongly correlated with plant growth. Gardeners, greenhouse managers, growth chamber users and salt-water aquarists measure PAR to insure optimal specimen health.