Having trouble blooming cattleyas and brasavolas

[Grim Tuesday]

I have several cattleya hybrids, laelias, and brasavolas that are large enough to be blooming size, I grow under quite high light conditions, and have now have failed to bloom for me for at least two years. The orchids live in my bathroom on top of the medicine cabinet; I have my lights mounted on the ceiling approximately 18 inches above the plants and are timed to a constantly changing sunrise/sunset schedule. The plants are in mostly medium size orchiata bark, I water weekly with a drench in the shower, fertilize with slow release pellets and they consistently grow a nice new growth for me every year, but have skipped flowering several times. I've gotten good blooms out of vandas and catasetum in these same conditions. What am I doing wrong for the cattleyas?