As a longstanding wizard force within the Ulnas Circle, the Pure Light Court is generally not associated with the Metal Ancestor Dragon.
In addition, the Pure Light Court is very dominant, and failing to detect something conclusive from a Light Wizard could likely provoke retaliation from the Court.
For these two reasons, to date, the glass ball that detects the presence of the Metal Ancestor Dragon has never been used on a Light Wizard.
Selena was probably the first in the Ulnas Circle to use the glass ball to detect a Light Wizard, and she targeted an eighth Circle wizard right off the bat, which was incredibly bold.
The results not only gave Lonco a big scare, but Jay Spade himself entered a state of complete petrification, never anticipating that he would be ensnared by a detection device.
How dare Selena detect him!
Wasn't she afraid of overplaying her hand and implicating herself?