experience with Metal Halide?

[mexorchid]

I'm missing some proper light for my cattleyas. Reading a lot on the topic, Metal Halide seem to be the best option for me but it's hard to figure out which strength to get.
I want to light an area about 125cm x 55cm next to a north facing window that now in autumn is not getting much sun (days are getting really short in Canada anyway).
How many Watt would you recommend?
And how far over the plants do I have to place the light with your recommended Watt? I also have some plants hanging on mounts over the table. I'm not quite sure what's the minimum distance from the MH light to not burn them.
Heat won't be a problem, I feel always cold myself.
Please share your experience and wisdom with me! Thanks

[naoki]

I've never used HID, but this table may help:



Top row (orange): lumen output/bulb (not useful for plants)
2nd row (yellow): bulb wattage of MH
left column (green): distance (inch)

The % values are percent equivalency to Sun PAR (sun PAR is about 2000 micro moles/m^2/s in full sun in summer).

So with 250W MH, you get 22% of the suns equivalent of PAR at 18" (440 micromoles/m^2/s).

If you double the distance, the intensity become about 1/4. This can be used to calculate the distance for higher watt MH (since the table only goes up to 20"). So with 400W MH, 17" gives 44%. If you put it in 34", you get 44/4=11% (220 micromoles/m^2/s).

People says Cattleya needs 2000-3500 foot-candle of peak sunlight in greenhouse. This means about 400-700 micromoles/m^2/s of PAR. But since this is the peak (noon) intensity and the sun intensity change over time, you can use lower intensity with constant artificial light. I think with most Cattleya, 10-20% sun equivalent PAR (200-400 micromoles/m^2/s) is probably a reasonable range (for artificial lighting).

[RandomGemini]

I don't know much about growing plants under MH, but I will add that when I had my MH setup for my reef aquarium, it drew a LOT of power, so I would make sure you sit down with your power bill, whatever lights you decide on getting, and figure out how much the new MH lights will cost you on a monthly basis. I understand that there are newer ballasts for MH lights that are more energy efficient now, but I would still make sure you do the math on that power bill. My power here is pretty cheap compared to other parts of the world and we had done the math and we were still pretty shocked when we saw the first bill!

Good luck!

[Joseia]

I grow exclusively under artificiallight since our home does not have windows with strong light. I use a Metal Halide light for the catts and dendrobiums and a combination of LED and High Output T5 lights for phals and some other house plants.

In regards to the MH light, it puts out ALOT of heat and also tends to dry out the air so I run a humidifier. I keep my MH light about two feet away from the top of the plants and have a fan blowing across the top of the plants to disperse the heat. One thing I learned is that light requirements you find online for various plants are really based on natural, outdoor lighting. I scorched alot of plants at first when I gave them 2000FCs of light. Under constant artificial lighting, you need much less. For me it seems to be around a third, 600-700 foot candles. Observe your plants carefully and watch for excessive purpling or bleaching. And slowly ease the plants in, give them time to adjust to the new intense lighting.

I bought a ballast with an adjustable wattage knob that gives me a wattage range from 250 to 600 so I can increase output later if I expand my growing area. I currently run the unit at 250 watts with the bulb about 2 feet away from the plant tops. I use a PlantMax 600w MH bulb and seem to be having good results so far. I'm a newb when it comes to orchids, but I have been able to flower B Nodosa Little Stars under the MH light, and my Iwanagarra Apple Blossom and Neostylis Lou Sneary are both currently spiking. Yeeha!

A couple of other things: hot MH lights can be easily shattered with water drops. If you water or spray your plants, be sure none gets on a hot bare bulb or it will explode with possibly dangerous consequences. Do not use a MH light if the outer shell is broken.

[mexorchid]

Thanks everybody for your input!
Naoki, very much like your table
Joseia, do you also find your MH light is using a very lot of electricity? What kind of reflector are you using?
A lot of heat wouldn't be bad because the orchids are standing on a heated platform filled with hydroton and water. I guess with more heat from the top there will just be more evaporation? I already have a fan and could mount it a bit closer to the light.
Good tip with the water sprays on the bulb, haven't thought of that!!!

[naoki]

Thanks for the info, Joseia. According to simple calculation here:

http://www.aos.org/Default.aspx?id=516

the conversion between intensity under constant light vs natural light is about 1:2. So the sun light with 2000 fc peak intensity gives similar cumulative light as 1000fc constant light.

So 700fc of MH gives about 106 micro moles/m^2/s of PAR, which is equivalent of sun with 1064fc peak intensity. I guess that your example shows that you can bloom orchids with way less than what is recommended for greenhouse growing (and those hypothetical calculation isn't enough). For example, with artificial light, you can give a longer day to compensate for it, or you never have cloudy day.

Here is the conversion table for foot-candle vs ppf for the calculation:

Conversion - PPF to Foot-candles

There are high performance LEDs (which can even come close to HPS efficiency), but the initial investment is still quite high.

[mexorchid]

Originally Posted by naoki

There are high performance LEDs (which can even come close to HPS efficiency), but the initial investment is still quite high.

Do you know more about which LEDs to use? I know how to build a panel with a heat sink, weld the LEDs and install the correct power converter. Instinctively I would use red ones of 2 different wave lengths, blue ones and many white ones to make the light not look strange in the living room.
But I don't know at all how many LEDs of which WATT to use and how close it would have to be to the plants.
I thought MH would make it easier because I need only 1 lamp that I can install higher above the table so it shines on the plants and hanging mounts. But hearing about the high electricity cost and that still you have to hang it relatively low... it's kind of making it less attractive to me. Then I can same build 2 or 3 LED panels in different positions... probably better?

[DavidCampen]

I would suggest that you use T5 fluorescents. A fixture with 4 4ft (120 cm) bulbs is 200 watts.

Here is a thread about an LED light fixture that I made:
http://www.orchidboard.com/community...your-home.html

[mexorchid]

Originally Posted by DavidCampen

I would suggest that you use T5 fluorescents. A fixture with 4 4ft (120 cm) bulbs is 200 watts.

Here is a thread about an LED light fixture that I made:
http://www.orchidboard.com/community...your-home.html

Are your plants happy with the LED light?
Somehow I don't like the T5s. They are one huge piece that has to be quite close to the plants, very inflexible to adjust to the landscape. I thought I could hang the MH light higher above the furniture but if that's not the case then different LED panels at different hights seem not bad to me. But maybe I forget to consider some facts???
Building the light isn't the problem; we made 1 big LED light for a sea aquarium which works very well. As long as you DIY LED is cheap.

[DavidCampen]

If you want to place the lights high above the plants then an LED fixture can be the best option provided that the fixture has the necessary lenses to focus the light. I use the LEDs as supplemental light since I also have sunlight.

Here is a photo of an LED fixture that I built. It is hanging about 6 ft above the plant table.