SightSensor HD and TC are presented to the network (and any VMS) as a dual stream ONVIF device. The streams are hard coded as Stream 1 and Stream 2. Any preferences for which stream to view is determined by the VMS you are using.
Unlike SightSensor NS cameras, the thermal stream in the SightSensor HD was designed for detection, and the HD stream for viewing. For this reason, it's expected that customers typically configure their VMS or monitoring center to view the HD stream during the day and if needed supplement that with the thermal stream at night.
In practice, we've seen situations where the HD stream, even in night mode with IR Illumination, may not be as clear as the thermal stream due to available lighting or other circumstances at the site. For that reason, some customers have chosen to view both streams in the VMS. Some VMS systems offer a dropdown where a user can select either stream based on preference. Again, this is a VMS-specific operation.
Refer to Viewing Thermal and Visible SightSensor Video Streams for more information.