max temp at plant tops vs bulbs ?

[Gunnarguchi]

i know the usual distance used as a thumb for distances for each wattage versus distance to bulbs but i want to use a wide range of different reflectors and bulbs

ive used my light meter and saw how rapidly the light intensity decreases so i think theres much to be gained in fine tuning the distance from bulb to plant tops adjusted to each wattage, bulb and reflector type

my idea is to use a max temp on plant tops to fine tune the distance for each bulb and reflector combination

this can be done in a separate environment paired with a light meter and a temperature measure if i just knew the maximum temp at plan tops

just using the hand or the rule of thumb for distance i think is to inaccurate for squeezing the last lumens out of the bulbs and converting them into maximum bud

any one knows the exact maximum temperature at plant tops for fine tuning in such a way ?

 

[dongle69]

The highest useful leaf temperature is 76 degrees.
For every degree of leaf temperature over 76 degrees, your plant loses 10% of its photosynthetic ability.
Use an infrared temperature meter directly on the surface of the leaf.

 

[Tony Aroma]

The highest useful leaf temperature is 76 degrees.
For every degree of leaf temperature over 76 degrees, your plant loses 10% of its photosynthetic ability.

Really? The temps at the top of my canopy are typically in the mid 80s. Your formula suggests that at 86 deg there should be no photosynthetic activity at all. Yet my buds are getting bigger and fatter, suggesting there is some photosynthesis going on. Am I misunderstanding something here?

 

[dongle69]

Most likely your photosynthesis is happening at a lower leaf level.

 

[YosemiteSam]

Is that temp the same in a CO2 enriched environment?

(and yes, the infrared temperature measurement is an excellent idea, really helps to show you what is going on)

 

[Calimed]

So my clones shouldn't be chillin in 80-85 degree's? Looks like I should turn my fan up

 

[geopolitical]

Yeah too high a temp and the plants start shutting stoma and plants start losing efficiency. I have absolutely NO clue as to what temps would induce this in your typical cannabis but I suspect that tropic adapted cultivars will tolerate much higher temps than those that grow in colder climes.

I've had plants that did well right up to 85 or so, and ones that did poorly at any time above 75 or so. Humidity, airflow, root system size, etc all will affect how a plant will weather higher temps.

 

[dongle69]

Is that temp the same in a CO2 enriched environment?

In the presence of enhanced Co2, plants can handle warmer temperatures.
I don't know the max temp in that case.

So my clones shouldn't be chillin in 80-85 degree's? Looks like I should turn my fan up

Rooted or not?
If they are happy, they are happy.
I'm just talking idealistically.

 

[dongle69]

To make it clear, I'm talking about efficiency.
Plants can certainly adapt to much higher and lower temperatures.
They just aren't performing their best outside of a certain range.

 

[purpledomgoddes]

plants, like humans, and every other living organism that seeks to survive, will adapt.

in nature, plants grow in high deserts, mountain ranges, dry valleys, etc. where the temps easily reach 80, 90, 100+ degrees.

w/ bare bulb vert 1k's, plants get as close as they want. 2-6" away. ambient temps 78-88f day+night. avg leaf temp 80-82.

maintaining the avg daily, weekly, monthly temp - whatever it may be set at - is the objective. the diff, or difference between day/night should be as small as possible. ideally 1-2*f changes during the season, never more than 10*f between day/night/week. if temps get up to 85 during day, w/ close light, night temp should not go below 76.

higher temps increase metabolism. only limitation on proximity of hid lights to plants is amount of air flow. w/ higher temps+lower rh (high vapor pressure deficit), plant will transpire profusely. gas exchange+availability of water to roots, w/ lower root temps than leaf, or ambient - all factors.

if closest leaf/branch to shows ill effects, move back 1-2". if not, keep them 3-6" under 1k, if rooted/mature.

hope this helps. enjoy your garden!

 

[Gunnarguchi]

tnx for all the replies so far

its not with added co2

reason for asking this in the first place is that i brought my meter in the small mother room i have with a 250 watt mh and began doing some reading with my light meter last night and saw how fast the light decreased over even small distances

so i guess the closer to the lamp the better and im also going to use several different reflectors to find the best for my needs ( not air cooled - not an option atm)

in order to have an basic readout to compare readouts each for bulb and reflector my idea is lowering it as close to the ground as possible until it hits the certain degrees and use that temp as a guideline for distance
then measure the distance for each bulbs and reflector to find the lowest possible distance without exceeding that max temp level

 

[sparkjumper]

Google fluke 62 mini for all your temperature needs.