HID lights?

[Fabolusus]

I have a 400 watt metal halide/hps convertible ballast and have been growing a wide variety of plants for a few years now. I just recently started collecting orchids (I have 7) and was wondering if anyone had experience growing under HID lights? I have a multi-tiered rack under the light that allows for many different "micro climates". I have done some reading, and was a little confused as most articles use the term "light candles" and I don't know what that means. My first orchid, a pink phal, purchased 6 months ago, is on the very bottom of the shelf, approx. 4 feet from the light. In this time, it has grown 5 leaves and two keikis. This gave me a little confidence and while on vacation in Hawaii, I couldn't resist buying 6 more! One epi. hokulea, 2 Cattleya that say "Slc. Volcano Dream, Volcano Queen", one Odontoglossum that says" Orchid Intergeneric", one oncidium that says"miniature oncidium" and one bare roots Arundina graminifolia (bamboo orchid). What I do with any new addition to my plant room is to start the plant off somewhere where it will only get indirect light or is shaded, and over a few weeks gradually move it closer to the light. I guess what my problem with the orchids is that I don't know how close to put them to the light. I know that different orchids have different light requirements, so some advise would be greatly appreciated!

[mayres]

I believe the term you are referring to is "foot candles"? The amount of light a candle throws on a 1 foot square surface one foot away = 1 foot candle. Low light orchids like phals 1000-1500 foot candles, moderate light orchids 1500-3000 and high light 3000-4500. If you don't have a light meter you can use a camera - set the camera at 25 ASA, set the shutter at 1/60 second, place a white sheet of paper where the leaves of the plant would be and focus on the white sheet from a distance of one foot. The f/stop will give you the amount of light - f/2=100, f/4=375, f/5.6=750, f/8=1500, f/16=5000. You will note that the light intensity will be 1/4 for each double in distance. I have personally only used fluorescents to this point because of the cost of MH and sodium vapor fixtures and the heat involved - but am intrigued and know that they are used by hydroponic growers and other commercial growers. Good luck and let us know how it goes. mike

[Fabolusus]

I can't do that with my camera!

[mayres]

Ooops! Sorry. If you know anyone who has a relatively inexpensive digital camera you can do the test. I have one that cost approximately $200 that can do this. A light meter would cost $60-120. Another option might be to see what we can find out about the theoretical output of a 400 watt metal halide lamp - I will help you do some research if I can. Keep in mind that with every double in distance from the light source you will reduce the footcandles by 1/4. Example: 2000 foot candles at two feet becomes 500 at four feet.

[mayres]

Okay see if this helps - I've been able to figure out the following. A 400 watt HID light produces the following foot candles at these distances - 3200 @ 7.5", 1600 @ 15.5", 800 @ 26". Low light orchids need 1000-1500, mid light 1500-3000 and high light 3000-4500. Keep in mind this is a NEW HID light bulb. You might be surprised how much they decay over time - usually replaced at least every year even though your eye will not see the difference. To read more try this link http://www.krischanphoto.com/gardens...ng/hid/hid.htm
Good luck - mike

[Fabolusus]

Thanks Mayres! I just sent you the technical specifications of the bulb I'm using...I don't know if it makes a difference!

[Fabolusus]

Ok, so I have one more question- of the seven orchids I listed, except for the phal, can you tell me which have low, med or high light requirements?

[mayres]

In general - catts 3000-5000, odonts 2000-5000, oncids 2000-5000. Epidendrums - medium light

[Fabolusus]

Thank you so much! I'll post an update in a week or so...

[Cynthia, Prescott, AZ]

I think the upper end on most Oncidiums and Oncidium intergenerics should be closer to 3500 fc. The Epidendrum and the Bambusafolia should be at the upper end. Cynthia