Since my last posting, I have been extensively reading on this forum and would greatly appreciate a knowledgeable critique of the design I have decided to move forward with. Again the purpose of this enclosed cabinet will be to house mature tropical plants to allow continued flowering through the long MA winter months.

Setup: 3' x 4' x 5' cabin made from plywood and totally enclosed on all sides. The front panel will be hinged so that it can be opened and closed like a door.
Inside walls and ceiling will be lined with Reflectix which is reflective insulation sold at Home Depot. I think this will help retain heat inside the cabinet since it will be placed in an unfinished basement space and could also serve to reflect the light around the space. This product is also not supposed to be affected by heat and humidity.
I was thinking of using a bathroom fan/heater combo to heat the space since the temps should stay at around 80F. This would be mounted near the bottom of the cabinet. I'm thinking heaters made to function in bathrooms should be able to handle humid environments safely?
I'm still confused about lighting! If I understand correctly from the information posted by various people here, I need a HPS light for flowering plants as opposed to metal halide? Is this correct? Will a 400W HPS light be sufficient for this cabinet? Do these lights generate a lot of heat? Since the walls & ceiling will have reflective material, would I still need a reflector hood?
For humidity, I was planning on setting up a water tray on the floor and since the structure is enclosed and heated, I figured it could do a decent job of keeping high enough humidity. Finally I was going to add a little exhaust fan near the top, back of the cabin to draw air out of the structure and keep circulation going.

So that is my plan - most nervous about the lighting aspect but really really hope to be able to figure it out and get it going. Please let me know what you think and I would be especially grateful to hear from anyone who has set up and operated such a basement structure - success AND almost-success stories would be great.

Thanks a lot

Is your purpose just to keep them growing, or do you plan to enjoy looking at them too? HPS light will work perfectly fine to keep them growing and flowering (lots of flowers), but you can't enjoy your flowers while this thing's running. The other thing that I've noticed about growing under HPS is that the leaves seem to turn a bit yellowish, even when I'm looking at it with my regular light on.

Also, since this is going to be your only source of light, you might want to spend a couple of extra bucks for a bulb with extra blue added to prevent laggyness and add extra vigor. The Eye Hortilux or Son Agro bulbs are 2 examples of that.

I grow orchids in my basement, under HPS, but I set the timer to turn the light off during the evening, when I get home from work. I then look at my plants under regular lights, or bring them upstairs for display.

Another option, if you want enjoy looking at them while the grow light's on, is the Ceramic Metal Halide light. This is because, it's got good intensity (for growing) as well as a very decent CRI (color rendering index).

Hope this helps.

As it turns out, I ended up buying a hydrohut type enclosure (4'x4'x6.5'), a 400W Hortilux super HPS bulb (has more blue added to the spectrum than the regular orange HPS), a timer for the light, an oil-filled heater, a temp/hygrometer and set the whole thing up in the basement. The plants went in a couple of days ago. Temps are fluctuating between 80F and 60F, humidity around 60% (bowl of water with cheesecloth to wick moisture down and a fan blowing behind it). Not sure if the temp fluctuation is too much and if humidity is high enough but I guess the plants will eventually let me know. Have some buds developing now and I think there is definitely some fresh green growth. I don't have the courage to try orchids yet but who knows, maybe one day.

Thank you for your input.
Amna

Lack of blue will tend to cause excessive stem elongation (particularly when temperatures go above 76F). Blue also helps in rooting and production of growth hormones.