To increase lighting or not?
 

Ok, a long winded explanation behind my questions:

I grow some miniature orchids in a 12x12x18 tall terrarium. Lighting consists of two cfl's (23watts, 5000k) under a reflector dome. I have a lux meter that has a footcandle mode. Based on this meter, lighting ranges from 450 to 2000 fc in the growing space. The orchids are growing like weeds but I want to make sure that I have enough light to bloom them and not so much as to burn them. Some orchids are sitting below their footcandle recommendation (according to places like Andy's), and are still turning red. For example, I have a Restrepia brachypus (see photo) that is growing like an absolute weed, which I love. However, there is certainly a red tinge to the leaves indicating that it is getting a sun tan (I think). I find this strange because the recommended footcandle range for this critter is 2000-3000 fc, and it is sitting around 1000 fc. Additionally, I have a Masdevalla nidifica that is still producing reddish leaves although sitting at ~450 fc (recommended is 500-1500). Growth is good, but again, I want to bloom them. I was originally thinking about upping to some 65watt cfl's in the 6500k range in order to accommodate a couple of high-light orchids that I want to put at the top of the terrarium, and also keep the lower- to intermediate-light orchids well within their recommended range. That being said, I don't want to overdo it. The lights are on constantly for between 10-13 hrs per day.

My questions are: Does prolonged exposure to less than adequate lighting equate to smaller amounts of higher light that an orchid might experience in nature? Does 10-13 hrs at 1000fc equate to more than ~3hrs at 2000?

Based on the situation, do you think I can stand to increase lighting so as to accomodate something that prefers the 2000-3000 fc range?

I have a Bulbophyllum lasiochilum that I'd like to move into the terrarium but I want to make sure that I can get it enough light.

Thank you in advance for any feedback and recommendations.

Is that 10-13 hr photo period a seasonal variation thing or an artifact of not running a timer?

Subrosa, the photoperiod is an artifact of not running a timer.

I'm guessing that you are equating the recommendation for greenhouse to the requirement under constant light. Most of the time, the recommendation for GH is the peak intensity (around noon). So under the constant light, you need much lower intensity. You can generally divide the recommendation by 1.5-2.

Even though CFL has very low efficiency, 46W for the small space is rather at the high end of many pleurothallids.

Since your plants are growing well, I would leave it as is.

To some degree, the longer day length can compensate. This is the basic idea of something called daily light integrals (DLI). However, the relationship between the light intensity and photosynthesis is not linear. So doubling the intensity doesn't double the carbon fixation above certain intensity.

The other issue with longer photoperiod is that physiology (e.g. flowering, dormancy) of some plants are influenced by the night length. Even within tropical orchids, some of them have this characteristics. But majority of orchids don't seem to show too much photoperiodism.

Naoki,

Thank you! Your explanation about constant light versus natural light in a greenhouse was perfect. That's exactly what I was wondering about.