growing under lights... how long?

[CJR66204]

Sbrofio-or anyone "How far do you or should I hang my LED lights above you my orchids?"

[Leafmite]

Just bought my first light so the timing of this was perfect!

[jeremyinsf]

Orchids don't actually wear watches.

There are several factors in lighting that have to do with "How much light" they get - not just time. The distance from the lights is a huge factor, imho more so than an hour's worth of time in many cases.

Yes some plants need a change throughout the year in how much they get time wise. But that's only one thing to consider.

18 hours a day would kill my plants. But it might work for others just fine.

[Laserbeak]

Most orchids that are grown for their flowers live in the tropics, where the day and night lengths do not change dramatically between seasons. With artificial light being weaker than sunlight, lengthening the length of the day cycle is a common way to make up for this.

Different orchids have different needs for darkness. In particular, some "hold their breath" over the day, and need darkness to open up their pores and exchange gases. Others do not have this requirement and can usually take 24 hours of light. Some plants also time blooming from length of day, especially those that are native to areas further from the equator.

You really need to look into the type of orchids you are growing to find out what their specific needs are.

[billc]

Originally Posted by Laserbeak

With artificial light being weaker than sunlight, lengthening the length of the day cycle is a common way to make up for this.

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That depends on how close you have the lights to the plants. I can burn leaves under my T5's fairly easily.
Another point to ponder.. sunlight starts out the day fairly weak, gets stronger during the day and gradually tapers off as the afternoon progresses. With lights you are giving the same dose of intensity for however long you have them on.

Bill

[naoki]

CJR, the distance between LED and plants depends on many things: intensity of light, light dispersion pattern, and requirement of your plants. If you have lens with tight beam pattern, you can place LED far away without wasting energy. DavidCampen has posts about his setup.

Laserbeak has a great, and easy-to-understand explanation! There are two aspects of day length (enough light for photosynthesis, and photoperiodism).

Jermey, plants may not be wearing a watch, but most plants do have fairly precise internal clock and circadian rhythm.

The conversion factor between constant light and natural light is about 50% (actually 40-70% depending on assumption). In other words: 1000fc artificial light gives a similar cumulative light as natural light with 2000fc peak intensity. But depending on the freq. spectrum, different amount of usable light is in 1 fc of light.

[orchidsarefun]

many of today's orchids are hybrids or primary hybrids. Cold-loving species have been crossed with warm-loving species. I doubt that many species would survive back in the "wild"
It would be just about pointless to trace back lineage and try to reproduce light requirements that way.
I go along with the "internal-clock" story - but for most people general guidelines regarding light requirements are "good enough"

[Laserbeak]

Originally Posted by billc

That depends on how close you have the lights to the plants. I can burn leaves under my T5's fairly easily.
Another point to ponder.. sunlight starts out the day fairly weak, gets stronger during the day and gradually tapers off as the afternoon progresses. With lights you are giving the same dose of intensity for however long you have them on.

Bill

Yes, this is all true and another problem with artificial lights. Since the strength of light diminishes with distance from its source, with artificial lights every inch you get away from the light, the strength of the light diminishes rapidly so even the same plant can be exposed to vastly different amounts of light energy. The sun, being 93 million miles away to begin with, a few feet (or even the height of the redwood trees) doesn't matter much so the entire plant gets virtually the same amount of light.

[The Orchidist]

I am using one of those cheapo tri meters for testing light distance , there is no wording on the dial but it lists 100....200 500 1000 and 2000 , I am assuming this is Lux or Fc level , If so most of my Chids are geting 700 , but as i raise it close to bulb it jumps dramatically , I almost want to shove a book or somthin under my trays . This would be with a 400w metal halide .

[Laserbeak]

Just to get a little mathematical, the energy of light is inversely proportional to the surface area of a sphere which is 4πr^2 where r would, in this case, be the distance from the light source.