Yes, you are describing the etiolation response mediated by phytochromes. However, the person who mentioned this may have some misunderstanding. Do you really think that etiolated plants perform better (higher fitness) than normal plants? They have to spend extra energy for stems instead of leaves, which is counterproductive.
Also the etiolation process is somewhat species dependent. In the grassland, etiolation may be beneficial because they could outcompete the grass. However, under the forest canopy, there is no hope that herbaceous plants can outcompete trees! So they shouldn't waste their energy for long stems. Most orchids are shade plants, so I would say that FR:R mediated etiolation is unlikely to happen (I know my Phalaenopsis pulcherrima etiolates when I put it in lower light level, though).
I'm NOT saying that FR is not required for orchids. Phytochromes mediates many responses, so FR "could" be used in a useful way to manipulate orchids, but I haven't seen a promising/convincing evidence (same for UV).
I'm looking forward to hearing how your project will go. With DIY route, did you consider chip-on-board (COB) emitters? It might be more cost effective for white based grow light. Here is some info which I saw recently:
https://www.circuitsathome.com/diy-2...ht-a-build-log
Cree CXA is better, but I'm thinking of playing with cheap COB from ebay (around $10-15 for 30W emitter + driver), and attaching them to CPU heatsinks from old computers.