Spiritual energy is something that cannot be seen with eyes and if it represents very high evolution very unlikely to be detected by physical instruments.
But one should remember that spiritual energy of a fully evolved person spans all of reality. You can imagine it as the size of spiritual energy if you want to have a simplistic understanding.
There is a lot more to it than tbe size. Incredible powers. But because people don't see it they so grossly underestimate the powers of a person who possesses such spirituality.
The size and power of a nation, a solar system, a galaxy or even the universe would pale into insignificance compared to that spiritual energy
Remember the kamadhenu episode between vasishta and kausika the latter after realization of the above truth went on to be called as Viswamitra.