Winter blues (coping with cold & dry conditions)

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I have grown cactus indoors under T8 fluorescent lights in a cold-winter climate, but not orchids.

You haven't mentioned temperatures. Also, if I read you right, your plants are getting almost 24 hours of light? You have the lights on at night and the plants are near a window? Most of our orchids are tropical, and they aren't adapted to very long days.

Your humidity 30%-60% is adequate and will not cause severe problems. But cold and dark will.

I might recommend turning the lights on before dawn, and off after dark, so the plants get around 10 hours of light. Turning them on during the day lets them supplement the natural light, so the peak light intensity will be greater than it is now.

What is your temperature range? This is very important for wintering orchids.