So I got a light meter- now what??

[astrid]

Hey everyone!!

I just bought a cheap light meter that reads in lux. First off, I hope that it is as simple as doing a mathematical conversion to get from lux to foot candles.

Now today is overcast. Some days get full sun, some days are cloudy. Obviously light varies on a day to day basis!!

I am wondering- how should I find the ideal light level for my orchids? Should I measure the lux on bright days, cloudy days, and in between so that I get an average? Should I out orchids in a place that maxes out at their maximum, or would this be too low of light for day to day growing?

I feel so unsure now!!

My windows face south, and I have no other options.
What do you guys think?

If a lux reader is useless to me, speak now or forever make me forfeit my Amazon return!!

How do I do lighting properly??

[AnonYMouse]

Measure on the brightest days. Rearrange plants according to their max light threshold.

[My Green Pets]

It's best done by taking readings over time.

Take readings at the same places, different times of day, for several days, until you start to get a feel for what your average daily light level bell curve would look like. You might repeat the process around the solstices and equinoxes to get an understanding of how light in your space changes through the seasons.

Watch how your plants grow. Observe each plant's leaf color, growth rate, and flower count. To track progress, take photos every couple of months and compare (and post on OrchidBoard ). You will see how growth and bloom cycles look for each plant. If you think they can take more light, give them more. I was pretty surprised to find out how much they can take. Remember it's the heat that cooks/sunburns the leaf, not the light.

To roughly convert to footcandles, divide lux by 10. For example, 10,000 lux = 1,000 fc. Good luck.

[Ray]

Yeah, that's close - 100 lux = 93 foot-candles.

There's a lot more to lighting than just the intensity. If you think of light as a "flow" of energy reaching the plant, then the intensity x the duration = the "mass" of energy reaching the plant.

When you see that a particular cattleya has a recommended light level of 3500 fc (~3750 lux), that's the noon peak, not a full daytime exposure. The total is actually about half the peak multiplied by the duration.

[astrid]

Originally Posted by Ray

Yeah, that's close - 100 lux = 93 foot-candles.

There's a lot more to lighting than just the intensity. If you think of light as a "flow" of energy reaching the plant, then the intensity x the duration = the "mass" of energy reaching the plant.

When you see that a particular cattleya has a recommended light level of 3500 fc (~3750 lux), that's the noon peak, not a full daytime exposure. The total is actually about half the peak multiplied by the duration.

Ray, do you care to clarify that math for me?

Would I multiply half the max recommended light by the number of hours? That would give quite a high amount of foot candles over the day.
I am not quite sure what you mean.

If you have links to any specific scientific studies or articles about that, I am a chemist, so any mathematical business doesn't bother me a bit!

[Tschimm]

Check Rays website Astrid. There's plenty of information available
http://firstrays.com/free-informatio...commendations/

Thank you for all the work Ray !

But are you sure about the calculation?
I thought 100 lux are 9.3 fc not 93

[astrid]

Originally Posted by Tschimm

Check Rays website Astrid. There's plenty of information available
Light Level Recommendations - First Rays LLC

Thank you for all the work Ray !

But are you sure about the calculation?
I thought 100 lux are 9.3 fc not 93

Well, if you did check the available information, you could confirm that 100 lux is 9.3fc.

Thank you for the link, however, it did not clarify the calculations I was asking about.

[Tschimm]

Ask naoki then. He's the light-measure-man here :-)

[Ray]

Originally Posted by Tschimm

Check Rays website Astrid. There's plenty of information available
Light Level Recommendations - First Rays LLC

Thank you for all the work Ray !

But are you sure about the calculation?
I thought 100 lux are 9.3 fc not 93

You are correct. Sorry!

---------- Post added at 09:03 AM ---------- Previous post was at 08:15 AM ----------

Originally Posted by astrid

Ray, do you care to clarify that math for me?

Would I multiply half the max recommended light by the number of hours? That would give quite a high amount of foot candles over the day.
I am not quite sure what you mean.

If you have links to any specific scientific studies or articles about that, I am a chemist, so any mathematical business doesn't bother me a bit!

If you grossly estimate dawn to noon to dusk as a triangle of light intensity level, then the volume of photons hitting the plant are 1/2 base x height, where "base" is day length and "height" is maximum light intensity.

That is particularly useful for folks growing under artificial light, but can be a help to those relying on natural sunlight, as well.

For example, if you have a 3600 fc noontime max for the plant, and consider dawn and dusk as zero fc, you can "chop" the day into 12 hourly steps, with each step have an average intensity of it's beginning and ending "actuals". For example if it takes 6 hours to reach 3600 fc, then that's a change of 600/hour. That means the first hour after dawn averages 0+600/2=300 fc, the second 600+1200/2=900, etc., up to the hours surrounding noon as 3300 each, then decreasing to dusk. So if you add those up, that exposure is 21,600 "foot candle-hours" during the full day. (That summation is 6x the peak.)

As full sun is on the order of 10,000 fc, a full-day exposure using that same estimation technique would be about 60,000 fc-hours. That gives you some parameters to play with:

• If you grew outdoors, you'd need 65% shade for all day exposure.
• If you're growing in an east-facing window, you'd probably be OK letting the plants get direct sunlight for the first 3 or 4 hours, then 50% shade until you lost the direct rays in late morning, (I'm counting on less heat due to indoor climate control.)
• For a west-facing window, just use the reverse, probably increasing the shade percentage or duration to compensate for the heat of late-day rays.
• If you lose sunlight sooner (or get it later) due to window placement, building overhangs, or local geography or trees, then it gives you a way to estimate the amount and duration of supplemental lighting to apply.