Light requirements - peak or average footcandles?
 

One question I've never seen answered definitively: when we see a particular requirement in footcandles specified for an orchid, does this refer peak mid-day levels of natural light or levels averaged through the day? For instance for a phal needing 1000 fc, would 12-14 hours at a constant 500 fc of artificial lighting (say at 5500K) be sufficient?

I wouldn't personally think so. I think that generally ranges are better indicators. Phals need between 1000-1500fc's and can in some instances (depending upon if it's morning sun, afternoon sun or evening) can take more. Under grow lights, I would personally aim for the higher end of the spectrum.

Hopefully Ray can answer this as he specializes in grow lights.

I think it would work. Light intensity outside is not the same over the course of a day, so a steady lightsource is going to be a long stronger than the average intensity outside for that orchid over the course of a day.

I remember that this was discussed here a while back, with any luck I can dig up the thread.

This reference would tell me what I need to know, if only I could determine the PAR factor for my 5500K CFL bulbs.

http://www.extension.purdue.edu/extm...O/HO-238-W.pdf

According to the chart, phals need an Average DLI (Daily Light Integral measured in Moles/Day) in the range of 4 to 10 (4 for good quality growing, but up to 10 for high quality).

The PAR factor (photosynthetically active radiation) isn't easy to google, as searches think PAR is a reference to parabolic reflector.

EDIT: Even though my bulbs aren't Sylvania, it looks like I can use a PAR factor of .014 for daylight CFLs.

http://assets.sylvania.com/assets/do...b1859b3bd1.pdf

or not, I'm thinking I'm getting my formulae crossed.

Oh, I overlooked this: To obtain conversion factors from lm/ft2 (footcandles) to μmol·s-1·m-2, multiply the above factors by 10.8

:shock: :faint: :faint: Much too technical for me!

LOL... Me too! However, Camille you make a great point about the light. Something for me to consider now that most of my orchids are back inside.

But as to one of the original questions about recommended fc being expressed as the maximum or the average over a day, I don't know.

O I love this stuff!

I can follow it....but not instigate it :blushing:
Sadly, my mind is not that good anymore.
When you come to the final equation of course that is my main interest. And I'm most appreciative of your work :bowing

By my calculation, 1 mole of photons with a wavelength of 630 nm (red light) has an energy content of 53 watt-hour. So, your range of 4 to 10 moles would be 0.2 kWh to 0.5 kWh. If your light source was 20% efficient at converting electrical power into red light then it would require an electrical energy input of 1 kWh to 2.5 kWh to produce the 4 to 10 moles of photons.

So to expand on this. Let us take the 10 mole value that I calcualte is equal to 0.5 kWh and convert that into foot-candles.

From the Perdue reference this 10 mol (0.5 kWh) figure is per square meter per day.

A square meter is approximately 10 square feet so the energy requirement is one-tenth of the 0.5 kWh or 50 watt-hours. Since this is over a ten hour period then the energy flux is 5 watts per square foot. A Candela is 1.46 milliWatt per square foot so 5 watts per square foot is 3,400 Candela or 3,400 foot-candle.