As with all of the gold rare dragons, Lumen is purely there as a filler. You may not even need him for breeding purposes right now, as you can get all of the dragons in the gold legendary range without using Lumen.
Breeding Lumen (link to Amoeba website)
If you wait until you have Whalegnawer, Lumen can be bred for just over 2,000 tokens with Ith.
Maximum Attack: 48,100
Maximum Health: 451,363