yes, but if I was seeing any of that I would pull light further away, but I am not seeing that...I have no tip burn,bleaching, twisting, etc...to be honest they really doing quite well.. I do not go by things I read, we kinda here to test for ourselves instead of rely on what others are saying, right?
When you read about that, it would have to be under the same circumstances we under, no supplemental lighting etc... I'm just not sure, that's how the "tests" were preformed...you know there alot of miss-information out there..
This is what I read........its by a clever bloke called DANGERDAN
its a great read too!! enjoy
Why Close Light Proximity Is Not So Important
12-25-2017, 03:09 PM
There is a large misconception in the hobbyist community, that having a light source as close as possible without any visible negative effects, provides the most optimal lighting conditions for plants. I will be explaining however, why this is not the case and to hopefully direct some peoples growing habbits in the right direction. Along the way we will be covering other topics that will help you understand the reasoning for this.
Some Light Physics:
Where the misconception of having a light as close as possible, was from the simple yet misleading idea that light in the form of photons, are lost or destroyed as they travel through space. Usually incorrectly associating the inverse square law as the evidence for this. This is not just exclusive for the hobbyist community but is also found to be true over other fields such as photography and lighting.
As i suggested, photons of light when travelling through space are not lost or destroyed. All that is happening, is photons diverge into more space and density reduces as a result. Because of the ever increasing space as photons travel, light density reduces with respect to the observer or destination. However, if all photons are somehow collected, the same number of photons would be recovered as the number that had originally left the source. The only time photons are deconstructed is when they interact with matter and converted into another form of energy such as heat.
Photons of light follow the
inverse square law only if the source acts like a geometric point source. What this means is that in order for photons to spread out over an area that is increasing in proportion to the square of the distance from the source. The geometry, size and shape must conform with that of a theoreticle point source that presents such characteristics. Now this is oversimplifying quite a bit, but it must be understood that, this rules out pretty much all practical lighting systems we have today. Meaning that all light sources will fall off less than the inverse square law. This is because, light will not diverge with the same characteristics as a source with a geometry that does comply with the parameters required for ISL. This is how we can create light devices that can travel extremely long distances before major degradation occurs. Such as lasers and spotlights.
Thought Experiment:
So we understand that photons are not lost or destroyed but simply radiate out as they travel. As such we can clearly see that a light source can produce a specific amount of photons per second. In this example we will use PPF here due to its relavence with this subject. For more information on measurement systems, read my other article
Light Metric Systems
If you have read my metric systems article, you should understand the differences between PPF and PPFD. PPF is a measurement of all PAR photons that are emitted from a light source per second. Where as PPFD only measures a specific surface area. If we measure a lights PPF we can get a solid figure on what kind of energy in the form of photons can be expected from such a source. However this is not typically provided with manufacturer specs of common light products. Saying that, there is good
data available that shows what kind of capacity certain light technologies can provide. When light is distributed such as that in a indoor growing environment (say 1x1m tent), all the photons from a light source, radiates in the direction governed by the source. So as to simplify our thought experiment. We will assume that light is uniformly spread and there are no reflection losses, with also all photons reaching the desired destination. If we now measure using PPFD (m2 surface area) system, we would get a reading of exactly the same as PPF. This is because PPFD is a per square metre measurment of a surface area. Which is exactly the size of our light environment example. Quantum meters with small sensors cannot measure electrical light sources in metres squared, as light is not uniform. They can only calculate uniform light such as the sun.
So as you can see, no photons of light are lost. This is because of the reasons discussed in the section on light physics. You might assume based on what has been said so far, that light height is of NO importance if there is no loss of photons. But there is more.
Realistic Practices:
Because there are reflection losses from radiated photons and because all light sources are different. The flexibility of the height placement is highly dictated by how the light is distributed. For small indoor grow environments that use reflectors, the most ideal designs are ones that collimate (light rays are parallal) the light as much as possible. Allowing the source to be hung higher with the least amount of losses from diverging photons. However, reflectors have been mostly catered for the commercial grow industry, having wide angle characteristics so as to allow commercial growers to develop environments where light is as uniform as possible. That said, being able to hang the light higher proves difficult because of these radiated losses. Its also worth mentioning that during the early stages of growth, the canopy in a grow environment will likely not be completely filled. Light sources that use optical lenses such as LED's, have a much more concentrated and collimated radiation. This means that height placement is more flexible and can be hung higher, allowing for a more precise and efficient configuration.
Plant Photosynthetic Efficiency:
Plants love making food through photosynthesis, but leaves have a limit on how fast they can do this at any given time. A leafs photosynthetic efficiency is called
quantum yield. This describes the efficiency at which a leaf can perform a number of actions per photon absorbed. The more actions that can be processed per photon, the higher the efficiency. The rate of photosynthesis and photosynthetic efficiency is limited by several factors including carbon dioxide, light intensity, temperature, oxygen, water, minerals, age, leaf anatomy and more. When there is not enough carbon dioxide to continue the increase in the photosynthetic rate, this is referred to as being co2 limited. When there is sufficient levels of co2 but low amounts of light, this is referred as being light limited. Outdoor plants typically shift between these two states throughout a regular day. During early and late hours when light intensity is lowest, co2 is not the limiting factor and as such it is classified as being light limited. During the middle of the day when light intensity is highest, plants are typically co2 limited. This is because the ambient levels of co2 cannot support the rate of photosynthesis from light absorbed from the sun. When a plant is limited by any of the number of factors that are relied on for photosynthesis, a plant will reach what is called the
saturation point.
When a leafs saturation point is reached, it will introduce
photoprotection to prevent additional damage caused by the excess light. This can be things such as chlorophyll or leaf movement, anatomical changes, non-photochemical quenching or thermal dissipation. This system essentially wastes extra energy and as a result quantum yield goes down. Once these biochemical protection systems can no longer relieve the excess energy, a process called
photoinhibition starts and the photosynthetic rate starts to slow down. Further reducing quantum yeild exponentially. Its at this point you start to see light stress symptoms such as chlorosis.
Cannabis Photosynthesis:
With small indoor environments, when a grow is well managed and healthy, usually light is the limiting factor before Co2. This creates a interesting discussion of when co2 should be introduced. With current ambient Co2 concentration, outdoor plants often reach the light saturation point (co2 becomes the limiting factor in photosynthesis) daily when light intensity climbs to high levels. Greenhouse growers with feedback systems fluctuate co2 concentration with respect to radiant intensity. When the saturation point is reached and quantum yeild goes down, co2 concentration is increased to maintain maximum quantum yeild. Other greenhouse growers use shade systems, that block light slightly when sun intensity is too high. Preventing these damaging systems from happening in the first place.
Cannabis has been shown
(chandra 2008 study) to start its saturation at around 500umls. This is actually similar to other species of land terrestrial plants. At 1000umls, the light saturation point is reached, this is about where any increase in light adds little to growth. Photoinhibition starts at around 1500-2000umls and photosynthesis rate actually decreases. With indoor lights and ambient co2 concentrations, you would typically want to have light intensity at the canopy to be around 500umols. With the highest levels to be no more than 1000umols for reasons previously discussed.
Conclusion:
So to sum up, having your light as close as possible does not provide more photons to a plant. Because photons are not lost or destroyed. Infact having the light too close can reduce the efficacy of your light source as the plant has many systems of processes that deteriorate photosythetic efficiency when certain paramaters are abused. Even though your plant may not be presenting any symptoms of light stress, these photoprotective systems can and likely are happening.
A cannabis plants best photosynthetic range is between 500umols-700umols as this prevents photoprotection and photoinhibition and allows maximum quantum yeild. However, hanging a light too high to achieve those levels can be not ideal. This is because light will diverge more, allowing light to completely miss the intended canopy and waste light as its turned into heat through reflection. So one must compromise between a plants health and the efficacy of the light source. Light sources that collimate and focus their light more (such as LED's), have more flexibility and can be hung to a more appropriate height. Allowing for a more effective distribution of energy to your plants.
I understand that the references of cannabis photosynthetic characteristics in micromols are useless to those who do not have quantum meters. As such i will provide tools to enable calculations of umols to lux. Where lux is the more common choice of measurement among growers.
Here you can apply conversion factors for light metrics such as photons in umols to lux. When applying the conversion you must select the right light source in order for accurate conversion factor. If you have an LED light source you can apply these conversions with satisfactory accuracy, if your LED system has white diodes. This is because the spectrum is very identical to that of high pressure sodium. If the color system is anything other than white, then the reliability of accuracy will go down.
For reference i will restate the cannabis photosynthetic characteristics in lux for HPS and white LED's.
Cannabis starts to saturate at around 500umols or 40,000 lux. The best range for photosynthetic efficiency is between 500-700umols or 40,000-58,000 lux. With the highest levels to be no higher than 1000umols or 80,000 lux.
by DANGERDAN
.....I turned the stand around on the Tyrone which dropped her about 2" is so im about(ish) same as you dude
........enjoyed your update too dude
...........I think you are a convert
