Darkness is maybe a challenge, depending on the speed, size and characteristics of the object. The sensors on board the different aircraft may have an ability to actually characterize, but that ability is dependent on a number of factors, including infrared signatures and electro-optical characteristics as well.
In this case, in order to have a better characterization of the object and its potential package, we scrambled fighters. That scramble led to an intercept just before sunrise. About five minutes after sunrise, that object crossed into Canadian airspace. That's why F-22s were on board and following and tracking the object.