light distance, temperature, and where to measure?

[keepleft]

hi all

 

i have always placed my temperature probe directly beneath the globe on top of the plant tips (therefore it would be measuring the hottest part of the plant). i try and make sure the temperature at this point is less than 30 degrees. with the 1000w hps, this means i need to keep the lilghts 60cm from the tips of the plants. generally the room ambient temp would be alot lower (24 degrees)

 

however ive read that you should measure the temperature away from the direct heat of the globe, eg against the wall or some other part of the room, at canopy level? and that provided that the ambient temperature at this point is below 27 degrees then it doesnt matter if the temperature directly underneath the globe is anywhere up to 40 degrees (for example). this is because the radiant heat from the globe would heat the probe.

 

can you guys give me some feedback as to where you measure temperature etc?

 

thanks

[Stoney]

i would do as you first said and put ya prob at the top of ya canopy under the light as this gives you a true idea of what temp the top of the plant is actually getting

 

although the thermometer i have is an inside outside jobby so the thermometer sits in one of me pots and outside probe goes to the top of me plant closest to the light so i get both readings

 

cheerz :Dj:

[thc24]

alittle while ago when trying to find the ideal light height, heat vs light output

 

 

i used/ borrowed a light meter basicly every 30cm light output drops by 100%. there is no way your going to be able to use a standard shade at 30cm, 50cm to 80cm would be a good range to start with.

 

 

then using 3 digi temp guages

 

1st hung and shade level

 

2nd mid way from globe to canopy

 

3rd at canopy level.

 

the only guage reading above 30c was the probe in shade. more guages = more accurate readings

 

i ended up settleing on 60cm from globe to canopy with a 600wt, 2nd and 3rd guage where simular abouts 25c and 28c in midle of lights on with fans running, thats about as hot as id like it.

 

 

In veg to make sure i get full coverage id go higher 80cm, and like wise for last 2 weeks to fill out all buds corner to corner. im sure youve seen how the euro folk do it KL sometimes there shades are 1m + from tip of plant pretty sure this to extend the light footprint from 1m2 to about 1.5m2

[two2time]

i put mine at the top of the canopy , best place for it..

 

 

tt

[Tom]

To set the light to grow height, start at a safe distance above the plants, hold your hand palm down level with the top of the plant for a few minutes. If it feels too hot on the back of your hand the light is too close, if cool then it's too far away. If it's pleasantly warm and it feels as if you could hold your hand there all day then it's OK.

 

[Shithappens]

Wow i place my thermometer at the plant hight on the wall closest to the light inside a flap of cardboard this is as good as ive ever needed heat rises so your ambient temperatures are gunna be around the same

 

This also depends on the type of thermometer too as some are for air the common in/out ones and do not correctly measure the air when hit directly by light. you really need a shaded air one as the differences in the way they absorb direct light will make them read different at the same levels from light.

 

As close as you can manage without the dreaded burn we all learn from burning our babies once or twice.

[keepleft]

hi all thanks for the responses.

 

im inclined to keep the temp probe at the canopy, but perhaps not directly beneath the globe. off centre perhaps

 

thc - its the euro folk that got me thinking. i was watching urbangrower videos and i see how they mount 1000's in a 1.6m2 foot print nearly 1m2 above the canopy. and im always trying to keep mine at 50 to 60 cm max

 

with the cool tubes, i can get the 1000's to 25 to 30 cm, but any closer than 20 cm and even if the temp is below 27 degrees the leaves get bleached from the light.... they go patchy yellow

 

ive ordered one of those infra red hand held thermometers, which you point and shoot and take the temp reading, should be fun to play with. i want to see what the temp of globe is for fun!!!

[Tom]

ive ordered one of those infra red hand held thermometers, which you point and shoot and take the temp reading, should be fun to play with. i want to see what the temp of globe is for fun!!!

Sounds more like a stoner toy than a grow room tool.

 

Where do I get one?

 

[keepleft]

hi tom i found them on ebay really cheap in the uk

 

http://cgi.ebay.com.au/BRAND-NEW-2006-INFR...1QQcmdZViewItem

 

they sell them at the hydro stores around here for $150 to $200! u can get em overseas for about $60 landed here. still wating for mine though....