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Terrarium lighting

Discussion in 'Orchid Culture' started by Sunfighter, Mar 27, 2019.

  1. Sunfighter

    Sunfighter New Member

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    I've been growing miniature Orchids in a small terrarium for about a year, but I'm still in the dark when it comes to light. I rrad about the footcandles required by different genera, but I have no idea how to know how much my aquarium LEDs are putting out. Seasons. My understanding is that there isn't much difference between summer and winter in the tropics. Arenm't these short day plants? I'm willing to adjust the photoperiod during the year if I need to, but do I?
     

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  2. naoki

    naoki Well-Known Member

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    You can use light meters (in fc or lux) or Quantum PAR meter (better, but more expensive). Or you can try Ray's method:
    Measuring Light Intensity ยป First Rays LLC
    You have to be able to access exif data of digital photo.

    With seasonality, there are quite a bit of variation. The day length may not vary much near the equator, but precipitation pattern does.

    I'm not sure what you mean by short day plants. Are you referring to the photoperiodism for flowering? In other words, photoperiodic plants are those whose flower induction is influenced by night length. If so, there are variations among different species. But some of them are photoperiodic. If you are interested, Joseph Arditti's book: Fundamentals of Orchid Biology has a table of how flower induction occurs for many orchid species (p.209-212).

    I personally change the day length by 1 hour or so (some year I forget).
     
  3. Sunfighter

    Sunfighter New Member

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    Thank you Naoki for the very helpful information. Short day plants are plants that don't normally experience days much over 12 hours in length. I have the timer on my terrarium set for a 9am to 9pm cycle.
     
  4. naoki

    naoki Well-Known Member

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    It is probably not too relevant how long the plant experiences day light in its natural habitat (unless their physiology is influenced by the photoperiods like long-day or short-day "flowering" or like the induction of dormancy from the photoperiods).

    From the perspective of growth (photosynthesis), day light integrals (DLI) of photosynthetic photon flux density (PPFD) is probably more relevant. That is the total amount of light received in a day. Within a reasonable range, you can use weaker light for a longer time. This is a bit of simplification because if you use too strong light, the rate of break down in photosynthetic mechanism (something called Photosystem II is the common part which breaks down) accelerates. This phenomenon is called photo-inhibition (the process isn't completely understood yet). Also, in CAM-dominated plants daily growth might not be limited by amount of light (they are more limited by the CO2 storage during the night), so DLI might not be relevant.
     
  5. Ray

    Ray Orchid Iconoclast Supporting Member

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    I agree that the day length - by itself and not pushed to extremes - is relatively unimportant. Photoperiod-driven plants (some cattleyas, e.g.) respond to changes (shortening) in the day length.
     
  6. Sunfighter

    Sunfighter New Member

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    Thank you both. I've just been a little confused by reading about plants that bloom in the spring or some other season. How does a plan t grown under lights know?
     
  7. naoki

    naoki Well-Known Member

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    I wonder that, too. Photoperiod is a good cue for the seasonality because it will tell them the absolute time of the year. Some plants are strictly photoperiodic, but more frequently others use it as one of many cues. For example, my friends transplanted poplars from southern and northern populations in Alaska. For some of them, they increased the temperature putting greenhouse like structure to each of them. Basically they were interested in how trees respond to the global warming. The northern and southern trees behaved quite differently, and southern trees (probably using photoperiod) started to grow early and kept growing later in the fall because that is what they do in south. But early spring and late fall is dangerous in Alaska, and they could get killed because of freezing. If they don't get frozen, they can grow bigger, but it is a risky strategy. But they do modify the timing of growth by the artificial warming experiment. So in this case, they were photoperiod dominated, but they can modify their behavior by temperature.

    I use reflective grow tents, so the natural light is completely cut-off. But many of them seem to flower in the correct time. I have assumed that they are probably sensing small seasonal differences in the temperature. When plants are imported from the southern hemisphere to the northern hemisphere, it is interesting that some plants can acclimate quickly (in terms of blooming season), but others take a long time. For example, my Cattleya warneri took 2-3 years before it started to flower in the correct spring. It has been shown that some of Cattleya are photoperiodic. So I wonder that those phoeperiod-dominated plants take longer to acclimate when there isn't much variation in day length.