Paphiopedilum... what’s up?

We do not see far red. The white shading could filter it out and we wouldn't be any the wiser. In filtering out the far red the shading would also filter out a lot of heat.

 

spujr,
you have the light on for 20 hours? Doesen't that have a negative effect on the growth of the plants if they have a night period of only 4 hours?

 

Yes, spectra affect growth. So does intensity.

I seriously doubt, however, that light reflection from adjacent leaves has much impact, if any. In a rainforest environment, light from the broad sky has to pass through a long, circuitous path, reflecting off of multiple leaves on its way through. That both diminishes the intensity (compensated for by the huge area - a whole lot of dim light combining to become adequate light) and significantly shifts the spectrum.

To plants growing on a bench, the incident light intensity is orders of magnitude great than anything reflecting off of adjacent plants, so overwhelms it. That, and the fact that the amount of light reaching a plant from those around it is likely minuscule considering they are side-by-side.

 

I agree with Ray's position on this. Light intensity is the easiest variable to test and, all other arguments aside, should be the first thing tested. You can get a cheap luxmeter online if you don't have a smart phone that can support a lightmeter app like "lux light meter". The plants aren't crowded (mine are more crowded but I don't see this issue) so light spectrum would be the next hypothesis to test.

I don't think running the lamps for 20 hours is a good idea. The plants do need to rest, and as many orchids are (if I recall correctly) CAM plants they need that night period to prepare their metabolism for the next day. Perhaps Naoki can weigh in once we have the lux meter readings?

 

I want to be careful about what I say: I'm not recommending 20hr duration. However, in Phreds case I think he would be "ok" to extend to 14 for at least during the summer months. Also to clarify I don't think the duration would improve or solve the leggy growth habit, but I don't think it would hurt.

In my experience thus far, I haven't seen any problems with going 20hrs with orchids. It is a common practice among many crop species (wheat, corn, tomatoes, rice) in speed breeding where they can generate 2-4x the generation turnaround per year.

That said, my experience doing this with orchids is limited to a few months and a few species and is not a true replicated experiment with proper controls, so again I would caution in applying it to your conditions.

Like I said, the plants I have doing this don't appear to be negatively impacted by the extra long days.

This is a photo of a malipoense compot I got in end of March:


Same mid May:


Yesterday (June 1st):


I can't say they are growing slower or faster. All I can say is that they appear fine and grossin growing well.

 

You are right about CAM and I realize my crop examples in my post above are either c3/c4 types. So again, caution in the wind. I think skeptism is due, but I'm trying it anyways .

 

One of the reasons I asked Phred earlier which bulb model he is using is because there is a big spectrum difference between the 2700k and 6400k (both are 48" 54W):



I am not familiar with these types as I use something different but it appears the 6400 has almost no red spectrum.

 

I think those spectra plots may be a bit deceiving. You’ll notice that both are normalized on the green spike to an arbitrary value of 1.0.

In fluorescents and white LEDs, the color temperature is a correlated value- correlated to what a true, black body spectrum of that temperature would look like to the human eye. As the eye is most sensitive to green, it is logical that the 6500 lamp has a lot more green than the 2700 lamp. I’ll bet that if the true intensities were plotted, those other parts of the spectrum would be better represented.

That said, in both types of light sources, the lower-temperature phosphors do tend to have a broader presence in the reds.

 

I grow under LED tube lights and adjust the daily light interval from 14 hours/day in May to 11 hrs/day in November. It is a gradual change of 30 min/day from month to month. Max/min temps in the room are adjusted accordingly as well. From what I’ve read longer light interval does not make up for insufficient intensity.

 

My bulbs with the 11-14 hr daily light interval (referred to in the reply below) are 5,000k. Here are my specs.

 

I have a similar light setup using the 5600K model but @ 20W instead of 40.

I am still learning about what all the numbers mean, but the nice thing is that this info is useful for my work application as well as my hobby (orchids)! I'm thinking it might be interesting to explore the different bulb types (3200K & 5600K) to artificially "mimic" a day, where the 3200K bulbs are turned on a few hours in the morning and late afternoon and then the 5600K turned on during the day. I suspect the effects would be minor in relation to plant growth but still fun to try.

 

That would more closely resemble natural daylight, I think (with noon being the most intense part of a sunny day) which is when the recommended Foot Candles for each type of orchid are measured. I’m not sure of the benefit, though. It was recommended (and I’ve found) with my lights, that with the constant light for the entire duration of the daily light interval, one-half the recommended Foot Candles for each type of orchid is what is needed. That enables me to raise the lights to 24-30” above leaf canopy which is glorious headroom (with 3 tubes in each fixture over Catts and 1 tube over Paphs and Phals. I can’t tell you the foot candles, but it it really low (relatively speaking) because I measure PAR, but everything is growing and blooming well (except for the catts I repotted at the wrong time when I was still learning). But, they are coming back with new leads, so there is hope even when we mess up. Happy growing.