First time setup-problem w/ leaves yellowing
 

Hey board!

Here is my new setup that I got for Christmas. It's 20x20x30 with a bank of 4 ho t5 lights. There is one fan in the corner and the front has sliding doors. The temp is about 75 all day with the lights on for 12hrs. I think the lowest it's gotten is 60 at night. I have just been putting water in the bottom to keep up humidity and spraying them in the morning. Humidity runs btw 25% up to 75%

Right now, i just have two orchids you see in there. The main one has been sprouting new roots before i put it in the box. i had previously repotted when I first brought it home and all the roots had died so i was excited to see this new growth. So that being said the leaves were just in ok condition. Recently, I have lost 2 bottom leaves due to them yellowing and dropping off. I know this is sometimes normal but I see another leaf starting to turn so I'm worried. I turned my light so that only two bulbs are on and moved the pots all the way down in the space thinking the change of no light to the grow box was a bit too much.

Do you have any advice on what to change?

As long it is only the lower leaf that is affected I would not worry. It is normal for some Phalaenpsis to lose the lower leaves as it grow new ones.

This will be the 3rd leaf to drop off in a matter of 2 weeks. Is that not cause for concern or should I take it as adapting to the new environment? I knew it was normal to drop old leaves as new ones develop but i'm worried I will lose the majority of them.

I would say that there's something about the new setup that it doesn't like. Probably too much light, too suddenly. Any time you move the plants into a new setup, you should adjust gradually. For now, I would remove 2 of the light tubes and slow down the fan a bit - it's probably drying out the plants too quickly.

So the plant basically doesn't have any roots and there is one new root starting? If that is the case, I wouldn't use strong light. Active photosynthesis causes production of O2, and stomata needs to open to get rid of O2. Then it will lose lots of water. If roots aren't in a good condition, the plants can't supply enough water. As the response, it is probably dropping the leaves (to reduce the photosynthesis and supply the nutrient/moisture to younger tissues). Well, Phals are something called CAM plants, so this issue should not be as pronounced as in other plants. But it is probably nicer not to give it the full blast of light. Probably 1-2 bulbs are enough for now, and you can gradually increase the number of bulbs as the roots become better. Also it would be helpful to keep the night-time air humidity high (to minimize the water evapolation via stomata). If you can put a couple tupperwares/containers filled with water in the case, you should be able to keep the humidity above 60-70% passively in a closed enclosure.

Naoki above made a god analysis of the situation!

Thank you for such a detailed response!! Yes, the old roots are dead and I have somewhere around 13 new roots growing just under the surface with the majority of them at the top of the plant. The are anywhere btw nubbins and around 3in. I only have 2 bulbs turned on and I filled the bottom of the case with a couple inches of water. I've been misting in the morning and at night after the lights go off. Trying to get the undersides of the leaves. Hopefully, this will get the plant through the transition period. I'm just so happy to actually see growth for the first time even though I'll prob loose the majority of the leaves.

It's crazy to think I have tropical plants growing inside while there's 2ft of snow on the ground now! :waving

Thanks again!