MajorCoco
Well-Known Member
Hi,
I came across some old threads, which apparently proved inconclusive. I'm raising this again because someone mentioned that too much light could be the cause of the slow growth I saw in my plants. ( I should add that this was in relation to my use of LED lights )
I wasn't sure if the matter is now settled, or if there's still debate...anyone care to chime in?
Anyway, to kick things off...I decided to do some of my own research. Here's a summary of what I found...I'm not saying it's complete and infallible, but the information below is taken from published research papers. NOT forums, and I have tried to only repeat information which is backed by laboratory-condition grow experiments ( sadly the plants being researched were usually things like bean plants. Good independent research on weed itself is hard to find, but the results should hold for weed)
Here goes.....................
1. It is possible to give plants too much light. (It's called Photo-inhibition...I'll explain what that is below)
2. Giving plants too much light will have negative consequences for your grow (though it may not be severe).
3. One effect of too much light could be a reduction in relative growth rate. (Dynamic photo-inhibition)
4. Another effect could be leaf bleaching (Chronic photo-inhibition) although this can be mistaken for IR (heat) damage, which often accompanies photo-inhibition, since the two conditions often occur together.
5. Of all frequencies, plants are most sensitive to photo-inhibition in the invisible Ultra Violet light frequencies.
6. In the visible light band, plants are most sensitive to photo-inhibition in the Violet light frequencies, with a minor peak in the orange region.
7. The amount of light needed to photo-inhibit plants is a LOT, however it is difficult to know accurately how much light you are giving your plants unless you have access to an accurate photometer. If in doubt, just use the "Light Distance Chart" as a guide...google it.
8. The Light Distance Chart is based on HID light sources. LEDs may differ, whether for better or worse is unclear, and would probably depend upon what colour mix you are using.
9. MH lights are more likely to over-irradiate your plants than HPS, since they put out more UV light than a HPS.
What is "Photo-inhibition"?
Essentially, "Photo-inhibition" means that the PSII photosynthesis channel (the part of the leaf's "power-plant" which is most light-sensitive) is being continually damaged. This damage is mostly being repaired, but the repair work is expensive. It requires the creation of a protein (D1), which means fewer resources are available to the plant for new growth. On top of this, the plant also needs to safely get rid of excess photon energy which would otherwise give-rise to dangerous reactive oxygen species (oxidants). Getting rid of this energy safely takes time and also costs the plant energy. This means that development can continue to be stunted even in dark periods as the plant works to rid itself of the energy.
In laymans terms, if you give a plant too much light (particularly blue light) the sensitive chemistry-set in its leaves gets frazzled, and energy is wasted repairing the damage instead of helping to grow new leaves and stem. This means that your plant grows slower, despite looking relatively healthy.
What can I do?
You may not need to do anything. There are a thousand other problems that are more likely to cause problems than too much light.
Plants can also acclimatize to excess light, making the problem go away on it own over time.
If the growth isn't badly stunted then it may be because the plant has acclimatized. In effect it builds up a tan, which will eventually help resolve the problem (though you will technically be wasting Watts of lighting).
I didn't find the following bit in my research, but I would say that once a plant has its "tan", a reduction in light may end up making things worse...in the same way that very dark-skinned people in Northern Europe sometimes need to take vitamin D because their natural sun-protection means that they don't get enough sun to produce it naturally themselves.
If you are pretty sure you are giving your plants too much light, and they seem to be suffering a lot then reduce it! Move the lights further away, or use a smaller wattage. If your problem was due to photo-inhibition then your plants will perk up after a few days and should resume normal growth speeds. Simple.
So how much light is too much?
Good question. In many cases it seems unlikely that you will be able to give plants too much light without first running into heat problems. Very well-cooled HID systems, and perhaps LEDs, however may mean that you can over cook the light intensity.
If you have a photometer for measuring your grow then ~700 micromol m-2 s-1 should be the very maximum you use according to the research (unless you add CO2). Slightly below would seem preferable from the papers I've read, but these studies were not done on weed, so I think there must be growers with real-life knowledge of very high intensity weed grows. Anyone got a good light meter and want to jump in?
(In the experiment I've cited, which tested dwarf beans, maximum growth was achieved at 630umol at 25C, and growth was slowed by 25% when the plant was exposed to 1300umol....25% reduction in growth...that could be your buds!!!)
Links:
http://www.fsl.orst.edu/~bond/fs561/references/alves-etal.pdf
http://www.mendeley.com/research/photoinhibition-photosynthesis-causes-reduction-vegetative-growth-rates-dwarf-bean-phaseolus-vulgaris-plants/
http://www.ncbi.nlm.nih.gov/pubmed/11959126
https://docs.google.com/viewer?a=v&q=cache:kQjOTn-0FSwJ:xa.yimg.com/kq/groups/21666630/284778129/name/Photoprotection,+Photoinhibition,+Gene+Regulation.pdf+&hl=en&gl=uk&pid=bl&srcid=ADGEESjEV0GSHp0NSqmfDONgOJWL41ghFCO8qsRqgMLUEzFhcagqQIrtlh4xpY7lEKY2XTJAr9zrGWk8Rf9f5aigCf4oczEihrutBOt5zrW2c0R_5jpSgOs-Og3s939Gs3G8C6bfeHgH&sig=AHIEtbRb8ttr3wOcsRzTEqWfJ_7a--pC1A
---------------
Anyway...there's my little summary, in case anyone is interested!!? Thoughts?
I came across some old threads, which apparently proved inconclusive. I'm raising this again because someone mentioned that too much light could be the cause of the slow growth I saw in my plants. ( I should add that this was in relation to my use of LED lights )
I wasn't sure if the matter is now settled, or if there's still debate...anyone care to chime in?
Anyway, to kick things off...I decided to do some of my own research. Here's a summary of what I found...I'm not saying it's complete and infallible, but the information below is taken from published research papers. NOT forums, and I have tried to only repeat information which is backed by laboratory-condition grow experiments ( sadly the plants being researched were usually things like bean plants. Good independent research on weed itself is hard to find, but the results should hold for weed)
Here goes.....................
1. It is possible to give plants too much light. (It's called Photo-inhibition...I'll explain what that is below)
2. Giving plants too much light will have negative consequences for your grow (though it may not be severe).
3. One effect of too much light could be a reduction in relative growth rate. (Dynamic photo-inhibition)
4. Another effect could be leaf bleaching (Chronic photo-inhibition) although this can be mistaken for IR (heat) damage, which often accompanies photo-inhibition, since the two conditions often occur together.
5. Of all frequencies, plants are most sensitive to photo-inhibition in the invisible Ultra Violet light frequencies.
6. In the visible light band, plants are most sensitive to photo-inhibition in the Violet light frequencies, with a minor peak in the orange region.
7. The amount of light needed to photo-inhibit plants is a LOT, however it is difficult to know accurately how much light you are giving your plants unless you have access to an accurate photometer. If in doubt, just use the "Light Distance Chart" as a guide...google it.
8. The Light Distance Chart is based on HID light sources. LEDs may differ, whether for better or worse is unclear, and would probably depend upon what colour mix you are using.
9. MH lights are more likely to over-irradiate your plants than HPS, since they put out more UV light than a HPS.
What is "Photo-inhibition"?
Essentially, "Photo-inhibition" means that the PSII photosynthesis channel (the part of the leaf's "power-plant" which is most light-sensitive) is being continually damaged. This damage is mostly being repaired, but the repair work is expensive. It requires the creation of a protein (D1), which means fewer resources are available to the plant for new growth. On top of this, the plant also needs to safely get rid of excess photon energy which would otherwise give-rise to dangerous reactive oxygen species (oxidants). Getting rid of this energy safely takes time and also costs the plant energy. This means that development can continue to be stunted even in dark periods as the plant works to rid itself of the energy.
In laymans terms, if you give a plant too much light (particularly blue light) the sensitive chemistry-set in its leaves gets frazzled, and energy is wasted repairing the damage instead of helping to grow new leaves and stem. This means that your plant grows slower, despite looking relatively healthy.
What can I do?
You may not need to do anything. There are a thousand other problems that are more likely to cause problems than too much light.
Plants can also acclimatize to excess light, making the problem go away on it own over time.
If the growth isn't badly stunted then it may be because the plant has acclimatized. In effect it builds up a tan, which will eventually help resolve the problem (though you will technically be wasting Watts of lighting).
I didn't find the following bit in my research, but I would say that once a plant has its "tan", a reduction in light may end up making things worse...in the same way that very dark-skinned people in Northern Europe sometimes need to take vitamin D because their natural sun-protection means that they don't get enough sun to produce it naturally themselves.
If you are pretty sure you are giving your plants too much light, and they seem to be suffering a lot then reduce it! Move the lights further away, or use a smaller wattage. If your problem was due to photo-inhibition then your plants will perk up after a few days and should resume normal growth speeds. Simple.
So how much light is too much?
Good question. In many cases it seems unlikely that you will be able to give plants too much light without first running into heat problems. Very well-cooled HID systems, and perhaps LEDs, however may mean that you can over cook the light intensity.
If you have a photometer for measuring your grow then ~700 micromol m-2 s-1 should be the very maximum you use according to the research (unless you add CO2). Slightly below would seem preferable from the papers I've read, but these studies were not done on weed, so I think there must be growers with real-life knowledge of very high intensity weed grows. Anyone got a good light meter and want to jump in?
(In the experiment I've cited, which tested dwarf beans, maximum growth was achieved at 630umol at 25C, and growth was slowed by 25% when the plant was exposed to 1300umol....25% reduction in growth...that could be your buds!!!)
Links:
http://www.fsl.orst.edu/~bond/fs561/references/alves-etal.pdf
http://www.mendeley.com/research/photoinhibition-photosynthesis-causes-reduction-vegetative-growth-rates-dwarf-bean-phaseolus-vulgaris-plants/
http://www.ncbi.nlm.nih.gov/pubmed/11959126
https://docs.google.com/viewer?a=v&q=cache:kQjOTn-0FSwJ:xa.yimg.com/kq/groups/21666630/284778129/name/Photoprotection,+Photoinhibition,+Gene+Regulation.pdf+&hl=en&gl=uk&pid=bl&srcid=ADGEESjEV0GSHp0NSqmfDONgOJWL41ghFCO8qsRqgMLUEzFhcagqQIrtlh4xpY7lEKY2XTJAr9zrGWk8Rf9f5aigCf4oczEihrutBOt5zrW2c0R_5jpSgOs-Og3s939Gs3G8C6bfeHgH&sig=AHIEtbRb8ttr3wOcsRzTEqWfJ_7a--pC1A
---------------
Anyway...there's my little summary, in case anyone is interested!!? Thoughts?
