What does (blank) foot candles, mean?? Please Help!
 

Hi I'm confused..I've been growing orchids for about..3-4 years now, and I keep seeing that the way people measure an Orchid's light is by "foot candles"...Ok, so I know they're not ACTUALLY candles but what are they? For instance, about three months ago I bought a Lady of The Night (Brassavola nodosa), and I read that they need 2500 - 3500 foot candles. How do I which window in my house has that? I guess what I'm asking is for someone to explain this form of measurement..in depth. Sorry for sounding so stupid..I'm only 15. Thanks!



(P.S. I've successfully grown orchids for the past 3-4 years, but I still would like to know how to use this measurement. Otherwise, I'm just going to have to keep being "successful", with Orchids by chance.):lol:

Well...I don't know how to explain footcandles to you.

I do know in some of the older posts here, the topic has been brought up. On the top of the screen there are options to choose from. Choose "search". Type in footcandles in the search field and hopefully you'll get an answer that satisfies you.

In the meantime, Brassavola nodosa grows in bright indirect sun much like Cattleyas or Vandas do.

Thanks, I appreciate the response! :)

OrchidDragon,

I'll give it a try. Light intensity is measured in footcandles. 1 footcandle is equal to the amount light recieved by a surface 1 foot away from a stardized candle. So 100 footcandles would be equal to the amount of light that falls 1 foot away from 100 standardized candles. The way this is measured is with a light meter. I hope this helps.

and now we know :biggrin: Thanks trdyl, I'd been curious myself for a while now but too lazy to actually find out

Foot candles as mentioned is just a system of measurement. Light is also measured in lumens or Lux,

Foot candles are an English system and with the world going to Metric, you would have to search for a light meter in foot candles.

Lumens are more common on the inexpensive ($35) meters coming from China. 1 Lumen is about 11 foot candles.

Now the important numbers. Noon sun is 10,000 to 11,000.

Heavy shade is usually 2000, the light that goes through an outdoor screen (not indoor window) is about 4000.

Windows are difficult. All windows filter the light to a greater degree. We like to keep our homes cool in summer and warm in winter.

To make it a little more confusing, but I hope enlightening, sunlight is not the proper measure for your plants. Heat is the issue. Orchids would love full sun if the heat buildup in the leaves did not kill the chlorophyll. This is why orchids growing in trees do so well. They grow at higher light levels since the tree dissipates the heat.

Back to your windows, glass can magnify the heat like a lens. You need to monitor it. At the same time few windows will let 3500 foot candles pass through it.

I find that mine range from 600 to 1800. Florida shades its windows more than other areas.

A meter is the best solution. Especially if you intend to grow orchids seriously.

For your one plant, use a west facing window since afternoon sun is brighter (and Hotter) than Morning East windows.

Check the heat buildup by feeling the leaves. They will get very hot before the chlorophyll begins to die.

Last issue is that plants do not need to grow in these light levels. These numbers given are the amount of light the plant needs to initiate flower buds. Once the buds have set the plant can be moved anywhere to be enjoyed. Seedlings too young to flower grow faster in lower light.

Thanks for a very comprehensive answer, Jerry, that explains why a brief spell outdoors got a reluctant Dendrobium to flower at last.

Happy growing!

I might have to try my Den outside for a bit next summer as it's grown a lot but not flowered this year.

How long did you leave it out Heather, and what sort of light was it (I would guess your conditions are not far off mine).

Remember that hot spell we had in late June? When the indoor temps were 25 and it was about 18 outside at night, when we all complained about lack of sleep due to "the heat"? Well, it sat on the patio in direct sunlight from 10 till two each day and so did the other one I own and my Winterwonderland White Fairy. One out of three induced to flower and the new growth on the WWWF is phenomenal :rofl:

Yeah, I remember that hot spell, what nice weather we had for a change!

Ok, so Dens should be able to cope with the sunnier side our our English weather then.

I actually put it outside last night for some late afternoon/early evening sun. I know it won't make a difference to flowering this year, but as the sun had made an appearance I thought it might apreciate a bit more light than it would have got inside.

I had not really realised that windows could make so much difference to the amount of light getting in and thought my Den was getting full sunlight inside. Well I learn something every day. :biggrin:

Yeah, only in my case it is often the same thing I learnt yesterday!!!:D

Yeap, I know that feeling too :rofl:

Jerry, thanks for the info. I am trying to establish better lighting situations for my orchids so I recently purchased a light meter. It measures in footcandles. Were the numbers you mentioned earlier in lumens or footcandles? I know what you mean about the heat vs light. Very difficult thing to balance. It seems that sometimes you need sunburned leaves to get flowers. Especially in south Florida and with sun loving plants! I may need to rescreen my shadehouse. (not looking forward to that) I bought the meter to check that out before I started ripping things apart.

Unfortunetly I often see such responses as above stating noon sun = something and "heavy shade" = something else. While noon sun in Ft Myers on a blue sky day may be 10,000-11,000 foot-candles, I assure you that at 45 degrees latitude it is way less than that. I measure approx 4,000-5,000 foot-candles in full sun in June in northern Michigan. I grow most of my orchids at 2500-3000 foot-candles. Heavy shade here in Michigan measures closer to 700-800 foot-candles. I still say the only definitive way to know for sure the strength of your local light (sun or shade) is with a good light meter. Not the cheapy mass-produced ones, but a calibratible one meant to measure within a couple lux/lumens.

I know what you mean Ross. The meter is not the "end all" when it comes to figuring out your lighting situations (or problems). But it has been helpful. The first one I got was only $8 at Home Depot. Not useful at all. The sensor was on the same side of the device as the gauge. Made it almost impossible to read in tight spaces (like near the roof screen of my shade house). The second meter I bought was better. About $30 from Broward Orchid Supply. Measures in foot candles. Has a wand that allows you to measure the light directly on the leaf from more than a foot away. Most importantly it confirmed my concern about my shade house being too dark. Not only that but the distance from the screen, glass or other barrier is more important that I realized. Unlike outside where the light (even filtered) is no different at ground level or 10 feet. The number of inches from the screen really makes a difference.