Use the picture below to determine which Apogee sensor your PAR Sensor (PAR-BTA) has.

Starting in May 2023, all Vernier PAR sensors, including Go Direct^® PAR (Photosynthetically Active Radiation) (GDX-PAR), use the Apogee SQ-100x sensor head that is attached to the main cable using a P68-rated stainless-steel marine grade (M8) connector (see red arrow in picture below). This connector is located 25 cm from the sensor head.

If your PAR-BTA sensor does not have a metal (M8) connector then it is the older PAR Sensor that has an apogee SQ-110 sensor head calibrated for use in sunlight. The older sensor heads have different spectral response profiles than the new sensor heads (see graph below).

The graph shows the spectral response profile of the older Apogee SQ-110 sensor head (gray line) compared to the new SQ-100X sensor head (green line). An idealized PPFD response (dotted black line) is presented for comparison.

Note: The newer PAR sensors use different correction factors when measuring PPFD under water, under certain artificial lights, and in certain field conditions. For more information, see Can I use Vernier PAR sensors with electric lights? When do I need to use a Correction Factor?.

If you need the user manual for the older PAR sensor, click here.