Deneb is a bright star that forms the tail in the constellation of Cygnus .........?

Deneb is a bright star that forms the tail in the constellation of Cygnus “The Swan”. It shines at an apparent magnitude of “first magnitude” in our night time sky. Sirius, the brightest star in Canis Major “The Big Dog” is an A cl star like Deneb, but is the brightest star in our night time sky shining at a brightness of more than ten times brighter than Deneb. If they are both of the same spectral cl, what would make Sirius appear so much brighter and why?