Your growing area is very impressive. Inspirational, even.
Download a lux meter onto your phone (I assume you have smart phone, otherwise grab a teenager) and measure the lux. You can estimate about 20 PPFD per 1000 lux. I think Ray or Naoki was suggesting 100 PPFD is fine for our Paphs. The spectrum might be the issue rather than light volume. Too much far-red relative to red and blue light can cause stem elongation. Your shading devices might be filtering out the blue and red and letting too much far red pass?
True enough. If you use a growth stimulant that contains predominately cytokinins (kelp extracts made from Ascophyllum nodosum fall into this category), they will stimulate plant growth first, which in turn stimulates root growth. If the conditions are a bit awry, that plant growth can end up being leggy.Also, I'm assuming you haven't been applying any pesticides/chemicals? Some contain growth hormones that might cause similar symptoms.
True enough. If you use a growth stimulant that contains predominately cytokinins (kelp extracts made from Ascophyllum nodosum fall into this category), they will stimulate plant growth first, which in turn stimulates root growth. If the conditions are a bit awry, that plant growth can end up being leggy.
I doubt the spectrum is the issue. Yes, the plant needs light in the PAR (400-700 nm) range of the spectrum, but unless the light is really skewed to either end of that range, it's probably OK. White light is actually reasonably good about that.
Biologically, plants must have a certain "volume" of light, the intensity x time, both of which can be adjusted - within reason - to compensate for a change in the other. Each plant has its own range of volume needed to grow and bloom well. Too little of too much can be a negative.
I agree with what you say about light volume.
However I have reasons to suspect the spectrum could be a factor. In onions (bulb=modified stem, also a monocots), we seen bulb shape greatly affected by light intensity. If you plant an onion by itself and it receives high light intensity of full spectrum wavelengths it will have the tendency to flatten out, whereas in high density plantings under low light intensity with a modified spectrum of light the shape is elongated. Plants "perceive" crowding through the leaf canopy light reflection, ie the light being reflected off another leaf which is a specific ratio of more wavelengths of one over the other.
Of course, this is onion, not orchids, but there may be some relationship.
This the 2700k or the 6400k model?I do grow under lights. They are SunBlaster T5 - 54 watt high output bulbs with reflectors.
You changed three things: planting density, light level, and spectrum. How can you possibly know that it was the spectrum that affected the bulb shape?
Passing through a forest canopy, light intensity is diminished and the spectrum changes to having more green in it, due to leaf absorption and reflection properties. In Phred's case, the shading is white, so should have very little influence on the spectrum.
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