Depends on where you are. Latitude and what the air is like where you live. Desert type air or warm humid air? Here at latitude 33 something south i have my Cattleyas in direct sun filtered by two layers of 50% shadecloth in summer.
One layer of 50% shadecloth in "winter".

At this latitude with sometimes desert air some shading is necessary for all except the very tough.

Here at the 39th parallel, my C. mossiae gets FULL sun except for right now--it has a big, plump bud hangin' and it's about to open up! :-)

I'm with you on the gradual acclimation of the plant to full sunlight. It's the only way to fly!

That slight reddening? I think that it's merely an indicator that the plant is getting an amount of light adequate to produce visible pigment. How you choose to interpret that is up to you!

arthur, Thanks for noting your latitude! IMHO, that info is far more useful than agricultural hardiness zones!

--Stitz--

The slight reddening is a normal response to increased light. Generally regarded as a good sign, but I wouldn't increase the duration of sunlight further at this point. The reddening usually occurs when light is at the optimum level. The plant might like more light later on as it becomes more acclimated.

A color change that most clearly indicates too much light for an acclimated plant is a yellowing of the leaves. That happens when the production of chlorophyll can't keep up with the demands imposed by the light.

well, i'm just north of the 39th parellel in baltimore

do you keep it in full sun all summer?????

I think people under estimate how much sunlight big catts can handle. I have some in my screened in patio in baskets, and I know the screening material only shades about 30 percent. That means 70 percent of direct sun in South Florida. That is pretty bright and actually brighter than my vanda shadehouse which had 50 pct shade cloth.
I would suggest that you let the plant tell you when it is receiving maximum sunlight that it can process without stress. Look for a light to medium green color on your NEW growth. If you get yellow growths, than it's too bright and need to shade some more. Remember that the more light a plant receives, the stronger it will bloom. Think of the sun as a battery charger. If you increment gradually, you should be able to eventually figure out how much it can take. If you get some red pigmentation, use epsom salts at 1 TBSP per gallon and it will green up quickly from that point on. I try to use it every couple of months.

Cattleyas as whole can take a good amount of light. Red pigmentation is fine, like our reaction when we get a tan. However, if the leaves become yellow, or bleached out, then there is too much light. Very bright light will somewhat shorten the length of leaves and pseudobulb but bright light will help better blooming. The problem with bright light is really the build up of heat. Heat causes burning. If there is proper air movement, then the plant can tolerate more light. A swamp cooler helps keep down the heat. At least a good fan and added humidity. In the wild, these plants may grow in both filtered or unfiltered light, but at all times, there is a nice cooling breeze at the tops of the trees, and an afternoon shower to keep down the heat and increase humidity. Plus, there is a significant drop in temperature at night for the plant to rest. Cattleyas are intermediate temperature growers.

beaniebeagle,

I'm about 40 miles from you in Mungumry County. The simplest solution for me to determine the light tolerance of ANY plant is to gradually introduce it to full sun as you have written. If excessive yellowing or a burn mark occurs, it's time to back it off the light.

Even then, it's sometimes difficult to judge plants. Last year, I did exactly what we're describing--gradual acclimation to the sun with a bromeliad. The plant handled it well all the way to the summer solstice. The day after the solstice, the plant had a considerable burn!

The bottom line is that we need to be ever vigilant. When I grow outdoors, I know that I won't win a CCE award. My goal is to maximize the flowering from the plants.

--Stitz--