Supplemental light: PPFD vs Foot Candles

[Ray]

Originally Posted by rockyfarm

Thanks for your reply. With regard to the PAR meter; the output number might look the same for a source heavy with green light as for one uniformly distributed from blue through red, or even with red and blue peaks. Would our plants really benefit the same from each of these three?

No, they would not, as plants can react differently under different spectra. That's why having a PAR meter and spectrophotometer would be a valuable set of tools.

Your comment regarding chemical processing sounds very reasonable; one might think the longer daylength at lower light levels would give more time for efficient nutrient processing and metabolizing. Too bad we can't ask the plants for their preferences.

I don't think that would be clear thinking.

In equatorial regions days and night are roughly the same length of time and that shifts a bit seasonally as you more farther north or south. I would think that plants have adapted to those conditions of intensity and schedule, so I question whether trying to move them out of that "helps".

I honestly believe there are a lot more variables than we, the hobby growers, really understand, so we do what we can to "get by".

Even feeding is like that. All of the money put into plant nutrition research and it still comes down to "this worked, while that didn't", without a great deal of solid "and that's why" to back it up.

[rockyfarm]

Ray, I agree that the original species are adapted to the conditions they were collected from. I'm growing mostly hybrids (that might not even survive in their source sites), and I'm growing them in a locale where NO epiphytic orchids live, and it's in a basement, about as artificial as you can get. So I have to provide every component for their survival. Since my lights are 'on' or 'off' I have to pick a 'daylength', and that need not be at 12 and 12. In my working days I could measure oxygen production as an indicator of photosynthesis, and investigate productivity at various durations, spectra, and intensities. But I don't have that equipment here, and I want more than just maximizing growth rate of my orchids - they should bloom, recover, and resume growth. So, although it is a hobby (for me, anyway), I like to learn how to improve my cultivation. Thanks for your response.

[Ray]

Originally Posted by rockyfarm

Ray, I agree that the original species are adapted to the conditions they were collected from. I'm growing mostly hybrids (that might not even survive in their source sites), and I'm growing them in a locale where NO epiphytic orchids live, and it's in a basement, about as artificial as you can get. So I have to provide every component for their survival. Since my lights are 'on' or 'off' I have to pick a 'daylength', and that need not be at 12 and 12. In my working days I could measure oxygen production as an indicator of photosynthesis, and investigate productivity at various durations, spectra, and intensities. But I don't have that equipment here, and I want more than just maximizing growth rate of my orchids - they should bloom, recover, and resume growth. So, although it is a hobby (for me, anyway), I like to learn how to improve my cultivation. Thanks for your response.

Rocky, I am not disagreeing with your approach. I was merely trying to convey that while there is bound to be some adaptability, there are limits.

[Clawhammer]

Originally Posted by rockyfarm

I like the idea of integrating the PPFD value(s) over time (DLI) so I can manage daylength, under lights for optimum plant 'satisfaction'. I'm interested in cutting back the light intensities a bit to reduce their heating effect on my grow rooms.

I also grow in a basement. I do four things to reduce heat and ultimately my electric bill:

1) During hot summer days (95+) I turn off half of my lights, the next day I turn them back on and turn off the other half. My plants normally all get the high end of the light range and I think they appreciate the shady days. This can also be a strategy if your lighting is too intense and you need to spread out the light energy.

2.) I open up a basement window and door around 3am in order to help cool my basement before the lights come on. I use a fan in front of the door to drop my basement temp as much as possible. A couple hours of this seems to have a lasting effect throughout the day. It also seems to help keep the rest of my house cooler on hot days.

3.) I change the light schedule to have them come on in the very early morning so that they shut off before the hottest part of the day.

4.) Since my grow room is all concrete, including the floor, on hot days I lightly spray the whole room with water, duplicating a short rain shower. Not enough to wet the media, just the leaves, trays, and floor. The evaporation drops the temp 1-2 degrees, and slows down temp increases for at least 3 hours after the drop.

[camille1585]

Photoperiod can be extended with lower PAR levels for a lot of plants, but it has to be determined on a case by case basis. At my work (indoor farming) we know of some plant species which can have daylengths extended to 22h with limited side effects, and others are very unhappy if you push the boundries too much. Nighttime is important for plants as this is the period where a lot of important processes are carries out. As said above in earlier posts, there are chemical processes involved. For instance, one crop I've researched heavily can only photosynthize so much per day. Sugars accumulate in the leaf faster than they can be transported out and this transport happens mainly at night. If sugars aren't moved out they build up in the leaf and get converted to starch granules. These then crowd out the chloroplasts in the cells and give the leaves a chlorotic, blotchy yellow color.

Originally Posted by rockyfarm

Thanks for your reply. With regard to the PAR meter; the output number might look the same for a source heavy with green light as for one uniformly distributed from blue through red, or even with red and blue peaks. Would our plants really benefit the same from each of these three?

Your comment regarding chemical processing sounds very reasonable; one might think the longer daylength at lower light levels would give more time for efficient nutrient processing and metabolizing. Too bad we can't ask the plants for their preferences.

For your first statement that would be technically correct, a spectrum heavy in green would have similar PAR to one with strong red/blue peaks. However, how relevant is that comparision? You are never going to find any 'daylight' spectrum bulbs or grow lights which are green heavy.

[rockyfarm]

Originally Posted by Clawhammer

I also grow in a basement. I do four things to reduce heat and ultimately my electric bill:

2.) I open up a basement window and door around 3am in order to help cool my basement before the lights come on. I use a fan in front of the door to drop my basement temp as much as possible. A couple hours of this seems to have a lasting effect throughout the day. It also seems to help keep the rest of my house cooler on hot days.

4.) Since my grow room is all concrete, including the floor, on hot days I lightly spray the whole room with water, duplicating a short rain shower. Not enough to wet the media, just the leaves, trays, and floor. The evaporation drops the temp 1-2 degrees, and slows down temp increases for at least 3 hours after the drop.

Sounds challenging. I am lucky to be growing in a basement up north; mid-July it is still 65F (below grade). I've built a grow-room within this basement, fully lined with poly and with foam panel insulation on the ceiling and walls down to 4' above ground. The lamps warm the top part of grow-room to the upper 70's at which time a fan on the floor starts mixing in the cool air residing below the benches. I don't (so far) have to bring in outdoor air, and humidity runs 60 to 75% even without my mister running. In North Carolina I grow upstairs and it does get hot; I bought an evaporative cooler and place it on a drainage tray on a window sill (Amazon.com). This knocks over 5 degrees off the room temperature while keeping up humidity. I was surprised how well it worked even in a fairly humid southeastern locale.

[Kosmo83]

Originally Posted by Ray

Foot-candles guidelines are primarily based upon greenhouse growing under natural sunlight, to the numbers are the maximum levels to which the plants should be exposed. When dealing with artificial lighting that is constant, you should shoot for 50-55% of that recommendation (Read this), because the amount of light a plant needs is a combination of intensity and time, which is exactly was PPFD DLI is.

Hi,

i read your article and I agree with you for tomatoes or canabis, that a less intensity of umol/s/m² with a longer daytime is the better solution.

But CAM-Plants like Cattleya need a balanced Day-Night time, becouse they collect the CO2 only at night, store it and at Day they use it for fotosynthesis.

If this storaged CO2 is empty, the orchids stops fotosynthesis and a longer daytime doesn't have a positiv effect.
More, it has a negativ side-effect, becouse you shorten the time, CO2 can collected at night.
You can compensate it with added CO2 in the air, at trials at a japanese university an ammount of 1000 ppm CO2 is benefitial to the growth of cattleya.

2nd thing... at the equator, we can't see these extreme light-fading like we have far away from it.
I was in afrika near equator for holiday, the sun rises verry fast and at the evening the light fades almost immediatly, so the intensity-curve you draw on your article is good as example for a place far awayy from equator.

So my recomondation is not 50% of maximum light for tropic plants, better would be 70-80% of the intensity.

So if Cattleya get's arround 50klux/1000umol/s/m² at noon, the optimum are maybe arround 700-800 umol/s/m² for 12h

Here the sunpath-chart for moyobamba, peru

[Ray]

Yes, indeed. The sun path does change depending upon the latitude and longitude.

You can see your own HERE.

However, the recommendations given by most books and the AOS are generally based upon plants grown in greenhouses in temperate locations, so if nothing else, are a good starting point for evaluation.

I mean - really! Nothing in orchid growing is cast in stone.