When the Use Sensors checkbox is ticked for the first time, sensors are created:
Click OK, and the sensor placement dialogue box will open to allow the creation, editing or deletion of sensors:
Once sensors have been enabled, they can be placed, added and removed by using the icons in the RadianceIES toolbar.
Sensors can also be added and removed using the + and - buttons in the Sensor Settings Tab. The co-ordinates in the table can be adjusted to change the sensors positions and which direction they face.