Under lights. That's very intersting. I have a theory about artifical lighting vs. natural lighting and the bloom count of slipper orchids. I've seen it twice and now your delenatii might be a third plant. The theory goes like this, artifical lighting can extraordinary increase the number of blooms a slipper will produce vs. natural (sun) lighting. Now, the reason I say this, is because I have two plants one is a Phrag the other is a primary Paph hybrid and both came from previous owners that grew underlights (fluorscent). The Phrag pearcei (richteri) underlights would put up a three foot spike with ten (+/_) flowers, one at a time on it. In the greenhouse I get no more then four, maybe five per spike. The same thing with the Paph Herbert Barnhart (sp?), leimenaum X praestans, underlights it would bloom with nine or so and hold at least four open once it got going. Now in the GH I get four total before it goes out of bloom. I say lighting but it could be influenced by temperature or a combination. Of course my experimental numbers are low, two plants but it would be interesting to play a round with it moreI'm sure!
Yes, I'm growing under lights (MH 400 W)