PAR or PPFD Questions

[gideonupis]

I have long wondered about the overall determination of the amount of umols a plant receives. When you test the output of your lights at say 24 inches, that is usually testing at the top of the canopy level. But what about those areas below the canopy top? Does the plant distribute the received light values throughout the plant, or does each bud site on the plant need to be illuminated independently? That is, if my canopy top is receiving 500 umols, do I need to add additional side lighting to increase the amount of umols that those lower branches receive? Perhaps this is a stupid question, but I have always wondered and have never found any satisfactory information concerning it. Thanks in advance to anyone who can offer an answer.

 

[BigCube]

The plant is only able to photosynthesize so much light per square inch. Most of the good light is right up on the canopy. So you get to the point where more light up top doesnt get used, or even hurts photosynthesize. So yes adding that light into the parts of the plant that can still make near full use out of it is better.

The plant isnt really sending ppfd anywhere, it's doing work (photosynthesis) with it. The end result being carbon fixation (plant growth). Most sun loving plants tend to put most of their energy in to the canopy cause it wants all the light it can get, and that's where it is.

I guess the short answer is, the plant puts the growth where it will best be used to gather more light.

 

[Jimster]

Ditto on what @BigCube said. A little transfer might occur between sites, but for the most part, the energy that the plant gets stays where it was found. Direct light=bigger/faster growth. This is one reason folks will defoliate their plants, so that the shoots under the main canopy will suddenly get a big dose of light and grow qickly to fill in the gaps that you created. By doing this every few days lightly, by the end of flowering you can have a canopy of nothing but bud sites. I also take the larger fan leaves off of the growing larger shoots/branches to allow light to penetrate under the new growth instead of being shaded. It makes for bigger and fatter buds as you get more growth under the main bud site at the end of the branch, andeach one of those little shoots tries to turn into another branch... and ultimately, a bud.

 

[gideonupis]

The plant is only able to photosynthesize so much light per square inch. Most of the good light is right up on the canopy. So you get to the point where more light up top doesnt get used, or even hurts photosynthesize. So yes adding that light into the parts of the plant that can still make near full use out of it is better.

The plant isnt really sending ppfd anywhere, it's doing work (photosynthesis) with it. The end result being carbon fixation (plant growth). Most sun loving plants tend to put most of their energy in to the canopy cause it wants all the light it can get, and that's where it is.

I guess the short answer is, the plant puts the growth where it will best be used to gather more light.

Thank you, that helps a lot. You have told me exactly what I wanted to know. I thought that might be the case. So I will try to set up some decent side lighting as well as the overheads. That is one of the nice things about most LED fixtures. They can be adapted to that particular purpose. Thanks again.

 

[Jimster]

Thank you, that helps a lot. You have told me exactly what I wanted to know. I thought that might be the case. So I will try to set up some decent side lighting as well as the overheads. That is one of the nice things about most LED fixtures. They can be adapted to that particular purpose. Thanks again.

I grow a lot of sativa strains and I find that side lighting increases the yield and quality greatly,mostly because they grow tall and a lot of the plant is exposed besides just the canopy. Some strains that are shorter and bushier don't benefit nearly as much, as they are very bushy to begin with and almost al of their growth is on the canopy and not on the sides or under the main canopy. I try to surround my shorter plants with taller sativa so the best of both of them gets the light.

 

[gideonupis]

Ditto on what @BigCube said. A little transfer might occur between sites, but for the most part, the energy that the plant gets stays where it was found. Direct light=bigger/faster growth. This is one reason folks will defoliate their plants, so that the shoots under the main canopy will suddenly get a big dose of light and grow qickly to fill in the gaps that you created. By doing this every few days lightly, by the end of flowering you can have a canopy of nothing but bud sites. I also take the larger fan leaves off of the growing larger shoots/branches to allow light to penetrate under the new growth instead of being shaded. It makes for bigger and fatter buds as you get more growth under the main bud site at the end of the branch, andeach one of those little shoots tries to turn into another branch... and ultimately, a bud.
[/QUOT

Thanks to you also. I have done some cropping of the lower branches and fan leaves on my previous grow. It still ended up being somewhat christmas tree shaped with some largish buds on the side stems. Perhaps the side lighting will plump those up to decent sizes. Of the topic, but have you listened to The David Nelson Band? By your logo I would guess you will find them as enjoyable as I do. YouTube has quite a few performances, as does Internet Archives. And, as they said, "Let It Grow".

 

[gideonupis]

I grow a lot of sativa strains and I find that side lighting increases the yield and quality greatly,mostly because they grow tall and a lot of the plant is exposed besides just the canopy. Some strains that are shorter and bushier don't benefit nearly as much, as they are very bushy to begin with and almost al of their growth is on the canopy and not on the sides or under the main canopy. I try to surround my shorter plants with taller sativa so the best of both of them gets the light.

How do your side lights compare in power to the overheads? Are they about the same PAR output?

 

[BigCube]

I dont use side light. But I'm sure due to the closeness that the par output would be much less. Maybe 10% that of your main light. But also 10x closer. Any side light you use will be a hell of a lot closer than 20 to 30 inches. More like 2 or 3 inches.

The type of lights needed for side lighting arent normally tested for par values. They would be like flourescent tubes or the led equivalent.