Rising and falling footcandles

[sand_tiger86]

I've read something a bit curious a while back. I forget where, but it said that when an orchid requires, for example, 3,500 fc of light, that means that is the highest the light exposure needs to get up to for the day - not necessarily what it needs to be all day. So basically, as the sun rises and falls, at some point in the day the orchid needs at least 3,500 fc (preferably a few hours of it). Is that right? I guess in my naivety, I just assumed that whatever light an orchid needs, whether it be 1,000 fc or 4,000 fc, it needs that light as long as the sun is shining.

[wetfeet101b]

Add to that the fact that the effective photo active radiation (PAR) that lands on the plants throughout the year vary significantly as the seasons change.

When it comes to light, there are two main factors that need to be considered:
1. Maximum solar energy that the plant can tolerate. In most cases it is not the intense illumination that kills orchids, but the intense UV rays that piggybacks along with it.
2. Minimum PAR that the plant needs in order to perform photosynthesis - assuming the plant has access to water during the photoperiod.

The light ratings given by vendors for orchids are based on their growing conditions and what works best for the plant based on their experience. So the rating they give could actually be anywhere between the upper and lower end of the plant's natural range.

Barring special seasonal triggers, a plant receiving a consistent supply of light towards it's low-end limit could get the same results as a plant that gets fluctuating light supply that dips over and under it's natural range throughout the year.

Think of this simplified formula (although it might be more art than science)
Energy produced = (light intensity + water) x Photoperiod

To compensate for low light intensity, increase the photoperiod.
However, you can only extend the photoperiod so much before you end up depriving the plant of the dark phase that is also crucial for plant development.

Simple, right?

[sand_tiger86]

So in idiot terms (for myself), a plant that receives well-above its maximum fc recommendation for a few hours but not quite at it's lower end for the rest of the day could do as well as a plant that only receives it's lower end of light recommendation for longer periods of time?

*head spinning*

I'm only confused because I've read so many different things. I guess as someone else told me earlier, I fuss over these plants too much. I probably just need to let nature take its course instead of being so anal about every aspect of them!

[wetfeet101b]

a plant that receives well-above its maximum fc recommendation for a few hours but not quite at it's lower end for the rest of the day could do as well as a plant that only receives it's lower end of light recommendation for longer periods of time?

Yes*

* Assuming sunburn and dehydration does not occur on the former example and sufficient dark phase is provided to the latter example.

[wetfeet101b]

I'm only confused because I've read so many different things. I guess as someone else told me earlier, I fuss over these plants too much. I probably just need to let nature take its course instead of being so anal about every aspect of them!

No two plants will ever behave the same. You can set up two identical species in two identical conditions and chances are they will turn out different from each other.
So take every grower's word with a grain of salt. Unless your plants will be sitting right next to their plants, your results will be guaranteed to be different to a certain degree.

[Sirena]

I've been focused on making sure that my plant gets the right amount of light and water. It never occured to me that it would need a dark phase. How much dark phase would an orchid need?

[lijun]

I've been focused on making sure that my plant gets the right amount of light and water. It never occured to me that it would need a dark phase. How much dark phase would an orchid need?

Correct me if i'm wrong , from my understanding, at least about 8 to 10 hours daily.

[Halloamey]

Another important factor which has been forgotten here is the temperature which usually goes hand in hand with brighter light. A few hours with higher than recommended light would only be any good if the temperature is maintained at the cooler end, if the temp. increase with light it will result in scorching. And secondly few hours with more light is not the same as may more hours with less light. A particular threshold of light energy is necessary for the excitation of the electrons and the working of the photosystem. Imagine it like a mechanical process for eg. 4 men need 1 minute to push open a heavy iron gate, any less men and they will not be able to push open the gate, so 2 men even if they pushed for 2 minutes will not be able to open the gate.

[raybark]

I am likely the person who espoused the maximum comment referred-to in the first post (as I've never heard anyone else state that....).

Adding to Halloamey's excellent analogy, some time at higher light levels plus some time at lower light levels, indeed, does not equal all time at correct light levels. Not only is there the energy threshold issue, and the potential to negatively affect the chemical reactions that take place within the leaf by overheating, but there is the fact that the reaction rates are not linear with light intensity.

There are several different, but connected chemical processes involved, and they likely don't all happen at the same rate. You may push chlorophyll more with higher light, but that doesn't mean that the other associated reactions are going to keep up. And who's to say what "messing with" the relationship between those reactions can do?

A practical example is the lowly phalaenopsis: they do really well in the lower-light environment of many households. Transition them into an environment with higher light levels, and they can actually bloom less!

[lijun]

thing is,... i got this don't know how big/small this problem is,.. i did read about total darkness is also essential for orchids, other than lights. if it has similar function like how human body produce melatonin in darkness, or not,.. i'm not that sure, i haven't gone deep on this particular topic,..
but i don't have that darkness at night in my area, live in one of the main road here, many lights at night...