Day Length

[WaterWitchin]

What is DLI?

And PAR?

[thefish1337]

I believe Ray is talking about CAM processes. Phaleanopsis largely relies on CAM photosynthesis to produce sugars. There are optimum conditions during the light cycle and dark cycle and if they are altered, the plant will not grow to it's fullest genetic potential.

If you blast a phaelanopsis with too much bright light, photo-inhibition will occur- all of the organic acids (stored CO2 from the night) will not be well utilized to form sugars and the plant will not grow optimally. Too much light for too long will also keep the stomata closed for too long and the plant may not efficiently uptake CO2 at night as well.

Here is a paper that talks about this specifically with Phaleanopsis:
Photosynthetic Light Requirements and Effects of Low Irradiance and Daylength on Phalaenopsis amabilis

In CAM species, a short daylength would result in incomplete decarboxylation of the accumulated malate that inhibits stomata opening in Phase IV and thus lowers the nighttime CO2 fixation (Lüttge, 2008). The same results were observed in ‘TS97’ leaves in which the 8-h daylength nearly diminished the daytime CO2 uptake and caused a lower nocturnal CO2 uptake rate compared with those under the 12-h daylength (Fig. 5A–B). Although the 16-h daylength did not affect daytime CO2 uptake in ‘TS97’ leaves, it resulted in 5 h fewer of CO2 absorption and 25% less nocturnal total CO2 uptake than the 12-h daylength (Fig. 5)

In conclusion, the light requirement of maximal photosynthetic ability in P. amabilis ‘TS97’ leaves is ≈200 μmol·m−2·s−1 PPF and 125 μmol·m−2·s−1 PPF for low-light-adapted leaves. A daylength of 12 h maximizes the photosynthetic CO2 fixation and flower development. To reduce the cost of artificial lighting, 8 h of saturating PPF that is followed by 4 h of low light is sufficient for optimal photosynthesis. A constant high PPF above 320 μmol·m−2·s−1 under a 12-h daylength would cause photoinhibition and result in reduced CO2 fixation in Phalaenopsis leaves.

---------- Post added at 08:55 AM ---------- Previous post was at 08:50 AM ----------

Originally Posted by WaterWitchin

What is DLI?

And PAR?

Daily light integral (DLI) describes the number of photosynthetically active photons (abbreviated PAR, individual particles of light in the 400-700 nm range) that are delivered to a specific area (1m2) over a 24-hour period.

Highly recommend reading the link I posted, its pretty digestible.

[WaterWitchin]

Thanks TFish, I will try.

[WaterWitchin]

Thanks TFish, I will try.

[Ray]

It is far more complex. There are lots of chemical processes occurring, photosynthesis is just one, which produces sugars to fuel others.

The uptake of mineral ions is a chemical reaction, and how and where they are used and incorporated into plant tissues are others. Chemical reactions result in the formation of enzymes that facilitate/catalyze other reactions - photosynthesis, for example, relies on ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco), and that, itself, requires multiple, smaller reactions for form.

Each of them has its own reaction rate, which can be affected by any number of factors.

[thefish1337]

Regardless of the complexities Ray, you can use DLI and published and anecdotal research to find light levels that will be reasonably appropriate along side other recommended environmental conditions (water, feed, humidity, air movement). Phaleanopsis are one of the most well understood and studied orchids because of their commercial value. If you use well known cultural requirements (photoperiod, sensitivity to high light, day and night temperature differential, nutrient requirements) and published DLI values (4-6) it would be nearly impossible to provide improper lighting conditions.