From what it looks like the plants maybe getting to much light. Try moving them a little further away from where they are now. The yellowing is probably from too much light and is bleaching the leaves. They should return to their normal color in a short period of time.

The damage on the leaf could be heat related from the lights being too close. Or it could be you accidentally brushed the leaf against something without realizing it.

I do not believe the orchid is the culprit here. I believe it is too much light.

Dave

But they've been in this same setup for months. Would that change your diagnosis?

Wait, I lied, sorry! I DID actually lower the lights about an inch or two when I put the orchid in there. Do you think one inch will do that?

Light intensity increases and decreases with the square of the distance. This is more than most people expect.

Here is a link that might be useful: Inverse square law for light intensity

larius, while I appreciate the scientific answer... this graphic may have been more suited for me to get the idea ;-)

{{gwi:382157}}

BWAHAHAHAhahahahahahahahahahahaaaaaaaa

Here here!!!

I.

Diagnosis seems to be confirmed. Try moving the light back to the original position.

What type of orchid are you growing? If it is a Phalaenopsis they grow in the same amount of light as an African Violet. Too close will result in yellowing leaves or burning of the orchid as well. Orchids will take a little lower light if the humidity is sufficient. With the violets sharing the same area, there is no need to increase the humidity.

Dave

without the plastic, humidity was too low -- 35-40% I'd say. With the plastic, it's typically no lower than 50, so it helps a little.