What Triggers Flowering in Hoyas?

Every time I think I know the answer, I realize how foolish I am.  I have two different patella plants growing in two different tents with no access to natural light.  Day length is 14 hours and never varies.  Both patellas have budded up and are flowering right now.

Patella Bud - November 2013

Patella Bud – November 2013