This is only my 2nd full year growing them but in my opinion Lucifer is more robust in appearance. The leaves are 1.5-2 times as wide, it's supposed to get taller (to 4' vs. 3' for Emberglow) and the flowers are a bit larger. They're also a darker red with the Emberglow being more vermillion. Here's a close up of a Lucifer bloom.
