No religion here, a lot of observation and some science. First, there's light and then there's light. There's intensity (which can burn plants very easily, watch carefully because it can happen fast) and duration - how many hours a day the plant receives light. And spectrum. An outdoor-grown plant will get the natural spectrum of light, reproducing it indoors can be a challenge. And the whole thing is made more complicated for those growing indoors in higher latitudes, since sun shifts seasonally, at lower angles the higher wavelengths of the spectrum are filtered out by the atmosphere. I can say that with Phals, when I was growing them in the house, I went from essentially no reblooming to about 80% reblooming by adding supplemental light 12 hours a day. (took about a year to see the effect.. other factors such as temperature range stayed the same) Your experience may be different. Experience is the biggie here... observe, tweak conditions a little, observe some more.

Temperature differential is another factor - house temperatures tend to be very even. In nature, even in the tropics, there is significant day-night variation. Seasonal variation depends hugely on location - elevation as well as latitude.

As far as rest... that's another "it depends". I have learned (by killing several plants) that "dry" doesn't mean "bone dry" in most cases (Catasetinae somewhat and some of the summer-dormant Mediterranean-climate terrestrials are exceptions). In monsoonal areas where summers are wet and winters have little rain, there's still dew and humidity. There is a huge orchid-species nursery near me (like about 7000 species, somewhere in the neighborhood of 3/4 million plants) that I visit often (usually leaving significant amounts of cash behind :biggrin:), and have noted that the deciduous Dens, etc. are in the same area as everything else with the same temperature requirements. Everybody gets watered all year. The secret? Nearly everything is mounted, and so they all dry out quickly. Those Dens don't particularly get "rested" but they bloom anyway. (I think the owner, Andy Phillips, knows a thing or two about growing orchids, so I don't judge based on stuff I have read, I observe what works - even if it breaks the "rules" - and try to understand why so I can apply the observations to my own plants. I do know that Andy's plants don't have internet access, and besides they can't read. But Andy has not only years of experience but also the intellectual curiosity, and multiple plants of the same type with multiple microclimates, to experiment. And I get the benefit of all that by observation.)

So in short - it's all about learning the needs of each plant type, then experimenting - even those who live in areas that are natural for some types of orchids are likely to be growing plants that are native to someplace else. So everything we do is a compromise... the challenge is to find that sweet spot where what we can provide is a set of conditions that our orchids can adapt to.

In the reef aquaria hobby, when LEDs first came out people were melting their corals left and right, because they gauged how high to adjust the intensity of the new fixture by how bright it appeared to their eyes vs their old fluorescent or HID fixtures.

It can be beneficial to gather information (if available) or start with just a few plants to begin with ----- and start from some safe (or safer) distance. Start small, and learn/gather information/test ..... before going big.

If some kind of diffuser can be used, then that could help as well.

If you have various light sensing devices (lux meter, UV meter etc), then they could come in handy for assessing light intensity in various spots.

I grow my Cattleya in VERY bright and VERY hot conditions here in Texas. If I moved to RI, I'd grow all of my Cattleyas (mostly species) in full sun. The sun up there is very weak, even during the peak of summer and temperatures are very cool, compared to Texas, Arizona, or Hawaii, all places I've grown orchids. Its all about acclimation, as said many times in this thread.

However, your original post is asking about why your plants dropped leaves in summer. Can you post pics? There are a ton of reasons why this may have occurred, and none of those plants should have dropped more than a few old leaves.

I'm also wondering about the leaf drop. Sunburn usually appears as a white mark on a leaf that may gradually turn brown and die. I have however had plenty of sunburn on my plants without any of them losing all of their leaves. RI is much, much cooler than Philadelphia even in the summer so it's definitely not that it's too hot there. When I first read the title of this post I thought it would be about pests. Was it possible that you encountered some bad bugs that killed off all of your leaves? Mites tend to be the bane of my existence in the summer, especially on high light plants that grow quickly.

mites may have been an issue
i don't have pics of the dropped leaves, and most of the plants have regenerated. are there any threads on this board about acclimating stuff to outdoors for the summer? it seems best to keep things outside during summer
oddly enough, my cymbs and dends don't have any issue going outside in blaring sun without acclimation