Local news insists this is not for identification; they showed a view of what the sensor sees, and it looked like thermal imaging. Possibly intended to find people who are 'sick'?

ARLINGTON, VA: "Smart technology streetlight sensors have been installed in the Clarendon neighborhood of Arlington, as part of a pilot program to improve public safety in the area. The sensors can’t identify personal information about someone. Instead, optical, audio and environmental sensors collect information about the radius of location between pedestrians. The sensors were installed in June, with the purpose of seeing how sensor technology can impact public safety response.

“We have taken a location in Arlington County, in Clarendon, it’s a one block area, there are 10 sensors light fixtures that have been installed…The hope is to gather data and gather information that is helpful for us and our public safety team at understanding how they can respond differently,” said Holly Hartell, Assistant CIO, Strategic Initiatives for the county."

https://www.localdvm.com/news/virginia/streetlight-sensors-to-monitor-pedestrian-safety-arrive-in-arlington/