Can I use a Vernier Light Sensor to measure PAR?

The Vernier Light Sensor can not be used to measure PAR, photosynthetically active radiation. It does not have the right spectral response nor is it calibrated correctly. If you just want to measure PAR without logging data, Apogee Instruments, http://www.apogee-inst.com/quantummeter_options.htm has a good option. The QMSW-SS, which is a dual-calibration unit with a separate sensor, can be used to instantaneously measure PAR.
If you want to log data, it is possible that the Light Sensor offered by Qubit Systems, http://www.qubitsystems.com can be used. It works with LabPro and Logger Pro with a special calibration. It may work with LabQuest, although this has not been verified.