How to do the shadow test (and how to 'read' it)
 

Hello all! I understand that it is possible to estimate how much light is in a given area for plants by creating a shadow halfway between the light source and where you want the plant to go. The questions I have are...is that the correct method? And how much light is represented by each shadow intensity? I keep hearing very conflicting reports on this. Thankx in advance!

Try this link.... I'd guess that a Google search could bring others, but this one looks quite simple.

Thank you! By the way...are any orchids in the 'medium light' category, or are they all considered 'high light' plants? (I understand there is no such thing as a truly 'low light' orchid)

Short answer is yes, most of the commonly available tropical orchids can be grown and flowered successfully in medium light conditions.

There are some orchids that are considered low light. But in my experience, this tends to translate to "They'll grow, albeit slowly, in low light conditions, as long as other conditions are close to ideal, but they may not thrive or flower." This mostly includes Phalaenopsis hybrids, some of the thin, mottled leafed Paphiopedilums, and perhaps certain Jewel orchids such as Ludisia. Those same orchids can do quite well in low-medium light, provided you make sure that all other aspects of their care are as close to perfect as possible -- meaning raised humidity, warm temps (for phals), good quality water, good air movement, and so on.

The modern orchid hobby is geared heavily towards tropical orchids that can be grown indoors (outside of a greenhouse). In the average home, truly high light conditions are minimal, so orchids that need high light aren't all that common. Most things fall into medium light ranges -- of course low, medium, high are all subjective. So with a bright east or west window, you can find Paphiopedilums, Phalaenopsis, Oncidiums, Dendrobiums, Cattleyas, and plants from almost any other genera that will do just fine. That doesn't mean every Vanda or every Cattleya will tolerate it, just that you should be able to find a Vanda or a Cattleya that will.

OK! Thank you. Another question...my room has a daylight bulb that is sufficient (judging from the shadow test) to drive light levels into the medium range while it's on. This is intended to improve plant growth, but I realized a couple days ago that this could wreck havoc on getting blooms out of plants that require seasonal changes in photoperiod. Any suggestions for orchids that don't rely on photoperiod changes to bloom?

I use timers on the lights and seasonally adjust the length of time. It does matter, though the temperature changes are far more important to setting blooms.

If the bulb is in the ceiling or more than a few feet from the plant (depending on the type of bulb, wattage,spectrum, PAR, and other factors) then for all practical purposes it will have no effect on your plant(s), regardless of the "shadow test" results. This includes most common LED and fluorescent bulbs.

That being said, most of the commonly grown orchids aren't affected much by photoperiod. Phals, Paphs, Phrags, Dends, Oncids, and most others will be fine even if you're running the lights for long periods during the day. Pick something you like, and chances are good, someone here can help you figure out if it's a good fit for your growing conditions.

This is the way a lot of orchid growers start out, and in my opinion it can lead to disappointment. You're much better off getting a good idea of your growing conditions and then picking plants that you already know are a good fit. I see, and like, a LOT of cool-growing orchids but I simply can't adjust the conditions in my home to satisfy them. However, if it'll grow happily with a Phal then it'll grow in my home.

Low light plants: Some Lepanthes and Bulbos prefer low light (not all). These ones also seem to prefer a terrarium.

Obviously one can't make relations such as North window=Low light or South window= High light, etc.

I grow many orchids that require medium to high light in a north faced window because there's some white/yellow buildings in front that reflect sunlight. So, it's not a true north window light (if we can call it). But I can also put the pots near the floor the avoid that reflected light.

Also, in many south windows there are building or trees right in front.
You need to adapt and constantly monitor your plants to see if light conditions are really what the shadow test tells you.