Clearance needed under lights?

[AKNicolle]

I've got a bunch of fluorescent lights above trays in a room in the basement, currently providing lighting for my tropical bonsai, cacti, and soon some veggie seeds. There are five sets all told, each containing three T-5 full-spectrum tubes. From what I gather, they should be suitable for orchids.

My question is about clearance. The photo attached shows the clearance I have for three of the five trays. It's about 1ft or so between the tray and lights. The other two have closer to 2 or 3 ft clearance.

How much space would a typical orchid need? The lower lights would probably be fine for miniature varieties, but I'm new to this whole thing and have no idea how tall the flower spikes on orchids can get.

Does the spike have to be under lights also, or only the leaves? Would certain varieties consider this to be too much light, or is it impossible to provide too much light under indoor lights?

Thanks!
Andrew