Duration vs Intensity - Orchid Board

Phal grower · #1 11-06-2011, 06:18 PM

Hi all. I just wanted some input on this. When you are trying to adjust your lights to meet plant requirements do you play around more with the distance of the lights to the plants or the duration that the lights are on? I grow phals mainly so I don't need to worry about daylengh for flowering purpose's. What are your thoughts ?

Paul Mc · #2 11-07-2011, 07:11 AM

Well, growing over 80 tropical plants and now almost 70 orchids as well, my experience would state that you should be concerned about both.

If you have the duration but not the right strength of light, you can leave your lights on for a long time and it will do no good. I've lost many a tropical plant/fern to this because they were not near enough to the light to get what they needed or the intensity was not strong enough.

Conversely, if you have the right kinds of light but they do not stay on long enough to allow the plant to process enough energy to grow and survive, then that is bad as well.

Ray · #3 11-07-2011, 08:51 AM

Paul is right about "both".

Like most things "orchid", there is a lot of "it depends", or maybe I should say "yes and no".

Plants function on of PAR (photosynthetically active radiation), which is the accumulation of photons over time. One could argue that if a plant gets the correct amount of PAR from your lights (at a given distance) in "X" hours, then having them on longer would allow you to move them back (lower intensity), while still providing the necessary total. (As an analogy, consider filling a bucket from a fire hose and from a garden hose. The latter will take more time to fill the bucket, but in the end, it gets full either way.)

Within limits, it is possible to use time to compensate for light intensity, but there are several factors that limit it. For example, plants have different physiological processes going on when lit and when in the dark. Just as you need "so many" hours of sleep to "recharge" and be healthy, a plant has it's "down time" requirements, too. If you extend the "daylight" hours too much, you limit the nighttime hours, and can "wear the plant out". Many will recommend 14 hours on and 10 hours off to be a good split, with some adjusting to provide seasonality effects, if desired.

Similarly, there are energy-producing, and energy consuming processes going on while the plant is in daylight. As plants warm, both processes accelerate, but if the light level is too low, the "consuming" processes can outstrip the "producing" ones, which also weakens the plant.

Phal grower · #4 11-07-2011, 08:02 PM

Thanks for the input. I will continue to experiment and learn.

Eyebabe · #5 11-07-2011, 08:35 PM

Certain plants also need "seasonal changes" in order to flower.
Thus, shortening or lengthening the amount of time the lights are on will facilitate this.

When using lights, I place the plant the proper distance recommended and only supplement during actual daylight hours. Thus, my plants will have the seasonal variation of light time.

It's the seasonal variation in temperature that gets a bit more complex

Phal grower · #6 11-07-2011, 09:43 PM

True Eyebabe. I think that I will continue to leave the lights on for 14hrs a day. More for myself than the plants as I like to have time to mess about with them before and after work. I've been slowly raising my lights as I continue to have "tan" leaves.

Connie Star · #7 11-12-2011, 08:01 PM

I grow all of my orchids in a two story south facing room with lots of natural light. I also have artificial lights for the lower shelves on timers that I change with the season. I wonder about the room lights when I turn them on- often at random times- will that affect them?
We had a power outage for 3 and 1/2 days recently, so when the power went back on the lights were on at night rather than daytime, essentially giving some of my plants 24 hours of light until I realized it! I'm waiting to see if that has any effect.