Need a Comparison
 

I'm lucky to have purchased a used Orchidarium on eBay. But - I'm having some trouble growing my Catts. The unit has 6, 55w biaxial CFL's and can put out a lot of light. My question/concern is this: It says on the web in a couple places that Catts need something like 4000 ft/candles. If I use my light meter to put them at exactly a position that achieves that much light they lose their green color quickly and become washed out. So is that too much light? Or - is that kind of light so much that the Catts need more water/fertz? I"m not sure. Anyone else use a light meter and sure they have about 3 or 4k ft/candles and you're growing great?

Do you mean that your cattleyas become light green? That would mean they are getting enough light. Yellow, brown/black, or white would mean they are getting too much. There are some good pictures out there on the web that compare the leaves of cattleyas getting enough and too little light. Hope that helps!

Yes - I have some yellowing and some black spotting. Searching the web like you recommended makes it look like I'm definitely getting too much light. But I thought a light meter made things an exact science. Guess that's not true. Now I have to decide to lower the plants or reduce the amount of time they are exposed. Always another question. And - do plants that receive more light require more nutrients and water? I suppose so but how much?

Why not just turn off/remove a bulb or two?

When it comes to light, maybe catts can handle 4000 fc, but remember that that is the peak during a normal day in which the plants get zero right at dawn, gradually increasing to the peak, then decreasing again. The "area under the curve" is the amount of light they have received. In your case under lights, "dawn" til "dusk" is 100% - way too much light.

Your question about "how much" extra food and water do high-light plants need is very difficult to answer, as there are lots of factors that go into the consumption. I think the best thing to do is observe and experiment, keeping in mind that orchids don't need a great deal of food in the first place, and they store a lot of minerals, so even if you cut way back, it'll be months or even years until you see a deficiency (depending upon what is deficient).

Also, recognize that "more" food can be a factor of fertilizer concentration or frequency of application. Stronger solutions can be damaging, so I feed at about 50 ppm every time I water, and all of my plants seem to be happy, from low-light phals to high-light vandas.