Surprising discovery about my lighting

[Zabeta]

Hi everyone,

I just thought I'd share something I learned, for the benefit of others growing orchids at home or in windowsills (without grow lights).

I recently bought a light meter and was surprised to learn that my light levels (even in places I find bright) are very, very low - I mean in some places almost zero foot-candles. Even in a south facing room with large windows, being as much as five feet away from the windows (where it still seems bright to me) can bring the light measurement down drastically (to maybe 100 or 200 foot candles or even less than that). Even a foot or two away from the window can drop the levels precipitously.

And places where I had placed "low light" orchids receive light levels way too low for even those orchids.

I changed my setup so that the vast majority of my plants are now grouped on large tables and shelves in front of the windows (lower light in the back). Even this may not be enough light, although summer has yet to hit in full force (I suspect my sheer curtains will be necessary then).

This might explain why some of my orchids are subsisting rather than thriving.

When I was searching for information, I came across this very helpful article: Comprehensive Culture Guide—Light levels for growing orchids

Anyway, hopefully this will be useful to some of you! I was shocked to learn how "dark" my lighting seemed to my orchids.

[bil]

Originally Posted by Zabeta

Hi everyone,

I was shocked to learn how "dark" my lighting seemed to my orchids.

Yeah, I did the same. I was planning to put some phals on the front terrace, but was stunned at how low the light levels were.

[Zabeta]

Since I posted this, I have seen CambriaWhat's thread on the same topic (I got a light meter, and am surprised at the readings).

Doh! Should have checked the threads before posting a new one. But I do think it's interesting how apparently widespread the light problem is.

[WhiteRabbit]

A south facing window in the northern hemisphere doesn't get much, if any, direct sun this time of year through autumn (it's pretty much very bright shade). After that, it will start getting more and more, and in December, January, February is a good spot for sun lovers.

You bring up a good point about the distance from the window making more difference than one might think. I have narrow windowsills, so all my orchids are at most an inch or two from the glass.

And in regards to the sun moving to the south in fall, then back to directly over head during spring, it may be a good idea for some orchids to be moved seasonally to meet their light requirements.

[lotis146]

Man I think this explains more than I even know, including how much I should probably get a light meter.

I've got one of those 4 tier grow shelves from Big Lots in an east window which means some plants are nearly right up on the window while others are almost two feet away. Now I'm thinking as well that my south-facing window must not be nearly as bright as I think.

Perfect timing to find this thread given I just put most of my plants outside on a north-facing deck; I've been wondering if those nearest the back (Paphs) are even getting enough light. I'll share my results when I get a meter. Thanks for sharing.

[katrina]

Yep...it's why I've been saying for years that my light meter was an invaluable investment. Most people would be shocked at how little light their plants are actually getting. I know I was when I first got my meter.

[Ray]

That's a real testament to the human eye, too. It adjusts SO well, that we cannot detect what are actually large differences in light levels.

Another concept folks don't seem to grasp is that the glazing the light passes through (window or greenhouse cover) is perceived by the plant as being the source of the light. For example, in my greenhouse, high-light vandaceous plants do very well hung up high, about two feet from the covering, while phalaenopsis get their required lower light levels six feet farther away. Four times the distance would be 1/16 the intensity level if it was a point source, whereas, if the sun itself was the perceived source, the difference between "93-million miles" and "93-million miles plus 6 feet" is insignificant.

[Zabeta]

Thanks everyone!

Lotis and Katrina, yes, I totally agree that it's a worthwhile investment (mine was $20 from Amazon). I actually thought mine was broken at first because the readings were so low. :-/

This also explains a lot about my plants, some of which I've had for almost a year, and they are not really looking re-bloom-ish. My fingers are crossed that the increased light will make them want to flower!

[lotis146]

It really makes me wonder as I've rebloomed plants but honestly don't have really floriferous spikes. And some of my Paphs have been rather slow growing especially since I moved them to a lower shelf that I thought would still provide enough light... I can't get a light meter fast enough now! Thought about getting one a while back but then thought naaaa it's not that important...I guess we'll see about that.

[mtorchid]

Originally Posted by Ray

Another concept folks don't seem to grasp is that the glazing the light passes through (window or greenhouse cover) is perceived by the plant as being the source of the light.

Good point! And, even though we could agree the window is the source of light re the plant's POV, there is also diffuse light bouncing off floors and walls too. So, it's a little misleading to use a light meter pointed only in one direction when the plant is experiencing light from multiple directions simultaneously.

Plants with the same metered exposure in a room with white walls, light flooring will be receiving more light than in the same room that is later wood paneled and carpeted with a darker fabric.

Also, just as the angle that you're holding the meter will make a difference in the reading, the angle of the leaves to the window will also make a difference as to how much radiation is being received. A light meter will give you an idea of the light strength but there are many other variables.

I imagine that if an orchid was reading this, its response might be- "just look at the color of my leaves and that's all you really need to know" ;-)