HID Light - distance from plants

15 years ago

There is a recurring misconception concerning the distance that must be maintained between an HID light of moderate wattage and the top of an orchid plant, lately as represented in the article on light in May's issue of Orchids.

It must be a case of a greenhouse grower extrapolating what would seem to be a reasonable distance for house orchids grown with HID light as their only light source. The article suggests a wattage for a house grower of 400-600 watts and that works for me. But the author goes on to discourage higher wattage fixtures as being inappropriate for non-greenhouse growing. I think there are persons who are or have participated in this forum who use 1,000 watt fixtures in the house. But, that's another story. The author goes on to say that for said 400-600 watts fixtures, a distance of three feet should be maintained, else plants will suffer from being overlit or words to that affect.

I grow under 500 watts, 12-14 hours a day, in a small continually enclosed room with a little fan and portable swamp cooler that manages to keep RH between 45 and 50%, often less. The tops of my standard cattleyas are no more than 10" from the bottom of the fixture. And phals and paphs, maybe 4-5" more and not directly in the center 'cause that's prime catt space. I've never had actual burn on a plant, nor tell-tale bleaching out on any but old lower leaves, and rarely even at that. As a matter of fact, when I finally got over the idea of protective distance and boosted everything, paphs and phals suddenly became much fatter and more floriferous. And my catts are blooming much better now that I'm not being overly merciful. The bulbs are replaced every year and the glass lens is clean, so it's not a matter of my bulbs being dimmed.

Caveats: First, air circulation is probably key, but it's not particularly vigorous, and my orchid growing space is aired every night. Second, most of the time my temps peak at 82 or so and in mid-summer temps start to climb over 85 so I'm not talking about strongly intermediate or cool growers here, which are probably not great candidates for this type of set-up at any rate. In the warmest months I might consider lowering plants a little bit, but only after increasing air movement and observing signs of stress, and even then, certainly nothing near the distance that is often recommended for plants under that brightness of HID light. Three feet?? Third, the glass lenses that are recommended for these fixtures are huge heat deflectors and I wouldn't consider growing without one. And fourth, water and fertilizer have to be a little more optimum. Not "perfect", but regularly and dependably.

I'm not writing this to discredit the author, who I am sure has much more extensive general knowledge than I have about light. But when I first read on another forum that a hobbyist was growing an ascocenda 18" (or was it 24") from his HID light and wondered why it wasn't blooming, and then read this distance recommendation in the article, and in other sources as well, it seemed like a good idea to post about it.

FWIW,

John

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Comments (5)

mehitabel
15 years ago
last modified: 9 years ago
I have used 400Watt HID for growing orchids four winters, and had catts, encyclia, oncids and phals under them in that time. Some lights were on movers, but two are stationary. (This year it was four stationary, as one of the light movers died.) Two fans run 24/7 in the light room.

Also, FWIW, I agree with you completely-- most remarks about distances to maintain between the lamp and particular orchids are overly conservative. I never had any burn or light stress to catts or encyclia, even with the light quite close.

For phals, light stress only occurred for plants both close *and* directly under the bulb. If off to the side, they could be much nearer.

As you say, John, the fans probably make a difference. A fan makes a big difference with sun in a window, or even sun outdoors.

You need to experiment with your own plants to find a distance that produces the results you want in terms of growth rate and blooms.
westoh Z6
15 years ago
last modified: 9 years ago
I agree with mehitabel,

You really need to do what works for you, regardless of type of light. I don't use HID any longer, but with my current artificial lights I try to keep them as close as possible to the plants. Some plants within inches, some within feet... Depends on types of plants and strength of light. For example let's talk phals, I have some phals within 2" of 40 watt flouros and I have others at least 18" away from big bertha CFL's (haven't heard or used that term for a while ;-)), and all bloom fine. Same with some of my catts, I have a few (mini's) within 2" of 40 watt flouros that are currently blooming and others (Laelia/Lc.) within 4-6" of the bb CFL's that are spiking. Again depends on what the plants like, the minis can do with less light the L/Lc's like more.

I sure didn't put my 'kids within 2" of my 400watt HID when I used it, but then again I didn't keep the majority of them 3'+ away either as the article states. Over the last couple of years I've learned, give them all the light you possibly can until they tell you differently.

On a side note: John you should really consider looking at those big bertha CFL's (85 watters), replacing one 400 watt HID light with 4-6 of these and spreading them out a little can make a huge difference in getting maximum light to as many plants as possible. Aesthetics aside, I've seen a huge improvement in my plants since the switch. Mehitabel, with the light mover it may not matter as much, but something to consider if your ever loose the second one. I've been using my 85'ers instead of my HID's for @1 year, no issues at all and all bulbs continue to function fine. Plus best blooming 12 months I ever had in my 6+ years of growing. Energy use is about the same, I may see a slight decrease in overall grow room temps with the CFL's as opposed to the HIDs. My 400 and 250 watt HIDs are sitting in my attic, not sure if they will ever be put back in service by me.

Bob
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Any lighting that you use that will do the plants any good is going to appear pretty intense to anyone in the room, certainly far brighter than any normal room lighting would be. The UV should not be an issue, provided you work with the instructions and use properly shielded lamps. The UV that you do get is likely to fade curtains or even paint, that is exposed for many hours every day, but then that's nothing that the sun wouldn't do. You should be aware that not most HID bulbs are designed to operate either vertically or horizontally (or close to it), but not both. A few will work properly both ways. Most plant lights are designed with the bulb horizontal and the light directed downwards by a reflector. There is nothing to stop you clamping the reflector on its side, with the bulb still horizontal, and mounting it to the side of the plants. You might get issues with plants leaning, depending on how much light they get from the other side. Security lights are another source of HID lighting but they tend to produce a wider spread of light, not so good for mounting at a distance. The secret to mounting the lamp a long way from the plants is the reflector. If all the light is reflected in such a way that it lands on the plants then who cares whether they are two feet or twenty feet away. You'd need a pretty special reflector to work well at twenty feet though! Six to eight feet is do-able although best to aim for six feet I think. As for metal halide or HPS. If you just want to keep them ticking over during the winter, HPS should be fine. But check out whether you want your living area lit up by that particular shade of light. HPS is the most efficient plant light and it works well as a supplement to natural light. If you plan on using the lights for growing in the summer, you'll probably want about twice as much light and will probably be better with a metal halide, or maybe one of each, or perhaps a ceramic metal halide. Succulents will develop better colour and tighter growth with the extra blue and UV light in a metal halide. Here is a link that might be useful: All sorts of reflectors
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chryss
15 years ago
last modified: 9 years ago
So, tell me more about the bb CFL 85 watters. What kind of fixtures do you use with them ?? Are they the same as the corkscrew CFLs commonly used to replace incadescents ??

Chryss
westoh Z6
15 years ago
last modified: 9 years ago
Chryss,

Yes they are conventional screw-in with contained ballasts, just a lot larger than the standard ones you see, maybe 11" or 12" long and 4" across.

Most people use brooder lamps for the fixtures, they're available at the big box stores, but they really aren't the most attractive things, I grow in a spare bedroom so really don't mind the 'look'. I think a few places sell actual fixtures for these large CFL lights, but if memory serves me correctly they ran around $70-$90 without the bulbs. Some people make their own fixtures out of metal duct work, but they must be a little more mechanically inclined than me.

HTH,

bob
aerides
Original Author
15 years ago
last modified: 9 years ago
Thanks for the tip Bob. If the energy cost and heat are about the same, and with the HID fixture probably winning the aesthetic edge important (to me) in a shared living space, I'll look forward to a future foray into the world of CFLs. I think that same article on light gives a definite nod to fluorescent light regarding spectrum.

Studies must also have been done for comparative rates of light fall-off of HID and fluorescent light as well. I think that fluorescent light falls off faster and the increased headspace that HID light allows could be handy in an all-purpose setup.

John

HID Light - distance from plants

Comments (5)

mehitabel

westoh Z6

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HID Light - distance from plants

Comments (5)

mehitabel

westoh Z6

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chryss

westoh Z6

aeridesOriginal Author

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