Enough Light?

[Gthumbz89]

I recently moved and now have a southern facing window that I want to grow some cattleyas, oncidiums and phals. My light meter reads about 4,000-6,000 fc's in the morning (with a sheer curtain) from about 7-11 in the morning. After this period of time however, the light drops to 1500-50 fc's.

Is only 4 hours of peak light enough to bloom the higher light stuff like the cattleyas?

Thanks in advance.

[Ray]

First, you need to understand that catts, oncids, and phals have entirely different lighting needs. The first two can probably handle the morning light level, but I don't think I'd expose a phal to that - assuming your meter is accurate.

If you go by the old standard AOS guides, catts should see a peak of 3000-5000 fc, oncidiums 2000-6000, depending upon the type, and phals only 1000-1500fc. Peak intensity, however, is not the whole picture; you need to consider duration, as well.

If you picture the intensity as zero at dawn and dusk, and the peak at noon, the "volume" of light received can be estimated by the area of a triangle, whose "height" is the peak, and whose "base" is the hours between dawn and dusk. So if we assume a 12-hour day, the catts should get about 1/2 x 12 x 4000 = 24000 fc-hrs, while the phals only need about 25% of that.

That means that your 4 hours of high light (20000 fc-hrs or so) might be fine for the catts and maybe pushing it a bit for the oncids. As that's way too much light for the phals, just move them back from the window a bit.

[Gthumbz89]

Thanks Ray! So technically I should be getting 4 hours of nearly direct light so the triangle thing doesn't really apply. I get no light except for 50 fc's after solar noon (12:30pm.). Before then from a bit after dawn (6:30 am ish) I get 6000fc so really the formula should be this: 6000 fc x 5 hours = 30,000 fc hours. I fudged this a bit to not account for the brief 15 minutes or so of 1000 fc light before solar noon.

BTW the phals, paphs and miltoniopsis are very far from the window.

I hope this works because the photo-period is really short...perhaps too short for buds.

[Paphluvr]

What do you consider "very far"? Just remember the the amount of light the plants receive is the inverse square of the distance so the light falls off drastically as you get further away from the window.

[Gthumbz89]

Far enough that they only get a peak light exposure of 1500 footcandles. I used my cheap light meter to determine this. My miltoniopsis still looked a little burned, but it always looks kind of bad to me.

[katrina]

Are you sure it's a south facing window? My east facing widows get direct sun coming in before noon but my south facing windows do not get direct sun coming in until afternoon.

Also...as the sun gets lower in the sky as the fall approaches, the direct sun will become stronger for a time. At least until it becomes very weak. The same thing happens in the spring as the sun is getting higher in the sky.

One more thing to consider...depending on where you live...the daylight hours and light can become very low in the winter. I grow catts in a south window during the cold months but they would not bloom w/out supplemental light in the winter.

Just throwing that out there.