In article , Ray
wrote:

Xi,

I cannot answer either question, but I suspect it lies somewhere in
the fact that there are multiple processes going on in a plant:
photosynthesis (requiring light, obviously) which converts absorbed
water and carbon dioxide into sugars, a respiration process that
converts those sugars into ATP, the true "fuel" by which the plant
lives and grows, and then whatever processes go on to create more
cells to physically grow.

It wouldn't surprise me if there was some sort of "competition for
resources" going on that favors one process over another in different
lighting conditions, or maybe it's a heat dissipation thing...

I don't know the exact answer either, but the AOS book "Growing Orchids
Under Lights" by Charles Marden Fitch advises:
"Set an authomatic time to give 14 to 16 hours of light per 24 hours,
reduced to 12 hours for eight weeks in early winter." (page 8)
"Most species are day-neutral and bloom well with 13 to 14 light-hours
per period. A few must have precise combinations of light or
temperature changes to bloom freely." (page 40)
So, sounds as if have lights on 24/7, you might be discouraging blooms
and are probably wasting money.

You might want to buy or check out from your orchid society's library
the book "Growing Orchids Under Lights" by Charles Marden Fitch. It's a
small and easily read book, and it does have good advice.