Lighting question

Dendrobiums need lots of light but not direct sunlight. A slightly shaded south window would be best so i think it'd be fine. I am not sure about the rest but i know once you start seeing yellow folliage on an orchid, means you are exposing it to too much light.

 

That fixture will put out a LOT of light! You will be able to grow and bloom anything under it, even as a sole light source.

I think your biggest concern will be not burning them!

 

Keep in mind that artificial light output is constant. Natural lighting is not - it varies by time of day and by cloud cover. In general, somewhat less intensity in artificial light is more effective than natural. At peak natural intensity, the plants may be getting more than they can use, while at the evening and morning hours, less. With artificial, it's the same amount all the time. Consider it "integrated light intensity" - every hour, measure intensity, and add it all up, see which has the higher value...

 

This light intensity is inversely proportional to distance, and squared - half the distance = four times the intensity.

Yes, vandas can be grown under that fixture. I must ask about your "calculation..."

Carl is correct about the "integration" concept. If you take a recommendation for a plant's light level - let's use 2500 fc as an example - it is the most it should get at noon on a clear, summer day. If you look at zero intensity at dawn, the peak at noon, and zero at dusk, the path resembles a triangle (green line below), and the area under it is Carl's integration. That area is one-half the base times height, so when using artificial light for the same duration, the intensity should be 1/2 times the peak (the blue line), or in this example, 1250 fc.

 

Keep in mind that the inverse square law applies to point sources. A fluorescent lamp is not a point source, but closer to linear. So, for a linear source, the relationship would be closer to the integral of 1/distance^2, or just the reciprocal of distance. For a finite length illumination source, it's somewhere in between (you can get a reasonable approximation using a definite integral, I think). For six lamps, you'd have to solve that 6 times, using different distances. But definitely, inverse square doesn't apply to fluorescent lamps.

Your supposition about choice of genus/species is pretty much on target. Some large, leafy orchids will make nice shade for the plants that need lesser amounts of light.

 

Well, hopefully I didn't bring back bad memories. Once you mentioned engineer, I figured you'd have no objections to the math-y stuff.

So, your lights are bright enough, use big leafy plants to shade small low-light plants. Just like the outside

 

As you are using artificial lights and are concerned with what is the right amount of light for your collection, you might also want to consider controlling the humidity as well, especially if you are not growing orchids in a green house.
I grow some rain forest orchids under light in my home, such as smaller masdavallias, bulbophylums and draculas. I have a few very small cool mist humidifiers (my 5' X3' growing area does not call for a more expensive investment) and a very small fan (for air movement) that keep the humidity, at least near the humidifiers, at or over 70%. I even have a timer that turns the humidifiers on and off every half hour to try to imitate passing clouds. Many orchids that sat there doing nothing but look back at me month after month have responded to the higher humidity by growing faster and throwing out flowers. Even non-rain forest orchids have responded to the higher humidity. Of course, if you are lucky enough to have a greenhouse the need for a higher humidity will take care of itself as you water the orchids.
Have fun with this most intellectual hobby. It is very rewarding to bring an unusual orchid to flower.

 

Not to hijack his post, I was always wondering about suggested photoperiods for artificially lit plants. Suggestions?

 

Many folks go with about 12 hours in winter, 14 in summer.

Personally, I have gone with 15 year-round, which is convenient with my schedule. I do, however, increase the plant-light distance a bit to decrease the intensity of the light a bit to compensate.

 

Great thread, I have learned a lot. I had to google "Lorentz tensor transformations". It gave me a headache so I stopped.