What dose 'too much light' mean? Which physical parameter is related to 'too much light' term?
I think 'too much light' that cause light stress on plants relates to intensity and duration of the light simultaneously not separately. I think total light that plants get in a day determine how plants grow and flower. "Daily Light Integral" can determine total light with the dimensions(units) of
mol·m-2·d-1 [moles of light(mol) per square meter (m-2) per day (d-1)]. Right?
Light stress can cause by too much DLI that plants can handle in their circumstances (higher than their Crucial point). It's generally recommended getting the lights further away when plants show sign of light stress. Getting the light further away will increase footprint(m-2). so DLI will be decreased and drop below crucial point and light stress will fade away.
BUT... we can decrease DLI by one another way. Theoretically Decreasing number of hours that lights are running (watch out photoperiod 12/12 flowering schedule) will decrease mol.d-1 so DLI wil be decreased.
Overall, we have 2 options(or even more when we bring CO2 into the account) when we see light stress not 1. First getting the light further away and second decreasing number of hours that lights are running.
If plants don't need any darkness in veg stage we can hang light higher and run it more hours to support more footprint with the same results. This allow us grow more plants because we have bigger footprint coverage.
I know... We can decrease DLI in half by hungging light about sqrt(2) times(ISL) further away but to decrease DLI this amount by decreasing number of hours we need half hours that sounds impossible(lower than 12 hours per day will cause photoperiod plants to flower). Getting light further away is more efficient than decreasing number of hours but it doesn't mean decreasing number of hours of running light can't be a way to fix too much light prob (if too much light really cause by too much DLI)
Question: If my plants show sign of light stress slighty in 24/0 (or 20/4) schedule i can (and better) decrease number of running hours instead of getting lights further away. Am i right?
One more question. let me give you a background. DLI has dimensions of mol·m-2·d-1. We know it as average intensity in day that counts total photons each day the unit of area will recive. Each photon has its own known wavelength, frequency and energy according to Planck-Einstein relation law(https://en.m.wikipedia.org/wiki/Plan...stein_relation). mol.m-2 and energy per unit of area are basically equivalent. mol·m-2·d-1 has dimension of joule per unit of area.
We can consider 4 crucial point for DLI depending on CO2 level.
1st, minimum DLI to start successfully flower plants lower than that we get poor result. This DLI can cause use of must CO2 in free air... 380 PPM
2nd, medium DLI is Threshold for start supplementing with CO2 around 1000 PPM
3rd, high DLI is Threshold for supplementing with CO2 around 1500! PPM
4th, Extreme DLI is End point and higher than this will Definitely damage the plants.
Now I'm going to ask watts we need per square feet to reach those DLI point in a 12/12 schedule. We know each light emitting technologies have their own coefficient effectiveness so HPSs and LEDs shoud have different DLI crucial point(12/12 schedule multiple by coefficient effectiveness take place of joule so DLI can be determined by watt per square feet)
Help me to complete table below and correct me if im wrong. I know LEDs have no standard but thinking of well designed LEDs should give us some numbers... right?
If we know the numbers in a row of table above we can calculate the other numbers. Its sounds LEDs with correct spec are 30 up to 50 percent more efficient that HPSs. So those 2 numbers that are known to me should be around 97 and 112.
What is limiting plants not to be able to handle 75-80 watt/sf LED? H2O intaking?
6 CO2 + 12 H2O + LIGHT = C6H12O6 + 6 H2O + 6 O2
We can increase light as much as we want But above equation need 2 other factor to perform. 1 mol of absorbed light need(at least!) 6 mol CO2 and 12 mol H2O. This equation shows supplementing with CO2 when we dont have enough light will waste money. I think we finally reach a point for DLI (and CO2) unless we find a way to make plants uptake and use more H2O. and thats why we have Extreme DLI.
I think 'too much light' that cause light stress on plants relates to intensity and duration of the light simultaneously not separately. I think total light that plants get in a day determine how plants grow and flower. "Daily Light Integral" can determine total light with the dimensions(units) of
mol·m-2·d-1 [moles of light(mol) per square meter (m-2) per day (d-1)]. Right?
Light stress can cause by too much DLI that plants can handle in their circumstances (higher than their Crucial point). It's generally recommended getting the lights further away when plants show sign of light stress. Getting the light further away will increase footprint(m-2). so DLI will be decreased and drop below crucial point and light stress will fade away.
BUT... we can decrease DLI by one another way. Theoretically Decreasing number of hours that lights are running (watch out photoperiod 12/12 flowering schedule) will decrease mol.d-1 so DLI wil be decreased.
Overall, we have 2 options(or even more when we bring CO2 into the account) when we see light stress not 1. First getting the light further away and second decreasing number of hours that lights are running.
If plants don't need any darkness in veg stage we can hang light higher and run it more hours to support more footprint with the same results. This allow us grow more plants because we have bigger footprint coverage.
I know... We can decrease DLI in half by hungging light about sqrt(2) times(ISL) further away but to decrease DLI this amount by decreasing number of hours we need half hours that sounds impossible(lower than 12 hours per day will cause photoperiod plants to flower). Getting light further away is more efficient than decreasing number of hours but it doesn't mean decreasing number of hours of running light can't be a way to fix too much light prob (if too much light really cause by too much DLI)
Question: If my plants show sign of light stress slighty in 24/0 (or 20/4) schedule i can (and better) decrease number of running hours instead of getting lights further away. Am i right?
One more question. let me give you a background. DLI has dimensions of mol·m-2·d-1. We know it as average intensity in day that counts total photons each day the unit of area will recive. Each photon has its own known wavelength, frequency and energy according to Planck-Einstein relation law(https://en.m.wikipedia.org/wiki/Plan...stein_relation). mol.m-2 and energy per unit of area are basically equivalent. mol·m-2·d-1 has dimension of joule per unit of area.
We can consider 4 crucial point for DLI depending on CO2 level.
1st, minimum DLI to start successfully flower plants lower than that we get poor result. This DLI can cause use of must CO2 in free air... 380 PPM
2nd, medium DLI is Threshold for start supplementing with CO2 around 1000 PPM
3rd, high DLI is Threshold for supplementing with CO2 around 1500! PPM
4th, Extreme DLI is End point and higher than this will Definitely damage the plants.
Now I'm going to ask watts we need per square feet to reach those DLI point in a 12/12 schedule. We know each light emitting technologies have their own coefficient effectiveness so HPSs and LEDs shoud have different DLI crucial point(12/12 schedule multiple by coefficient effectiveness take place of joule so DLI can be determined by watt per square feet)
Help me to complete table below and correct me if im wrong. I know LEDs have no standard but thinking of well designed LEDs should give us some numbers... right?
| Minimum | Medium | high | extreme | |
| HPS | 50 | 66 | ? | ? |
| LED | 32 | 50 | 65 | 75! |
What is limiting plants not to be able to handle 75-80 watt/sf LED? H2O intaking?
6 CO2 + 12 H2O + LIGHT = C6H12O6 + 6 H2O + 6 O2
We can increase light as much as we want But above equation need 2 other factor to perform. 1 mol of absorbed light need(at least!) 6 mol CO2 and 12 mol H2O. This equation shows supplementing with CO2 when we dont have enough light will waste money. I think we finally reach a point for DLI (and CO2) unless we find a way to make plants uptake and use more H2O. and thats why we have Extreme DLI.
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