400w mh how far away from plant

[Padishah]

i tried the hand test and its cool but the leaves of my plants are clawed and one plant looks dryed up a little

400w metal halide right now its about 19 inches away

running DWC

 

[Padishah]

bump it up

 

[illusionz1]

I've got my week old ladies 25" from my 400 hps

 

[Krypt]

mine are 18" away and perfect, maybe you're underwatering or not getting enough air circulation, what are the grow rooms dimensions.

 

[Padishah]

room dims are 23" x 30" x 6' temp in the room is 75°f i was wondering if i need a glass shield to block the UV i have a fan blowing accrossed the plants running dwc with very low nutes to see if the plant recovers tried normal and it didnt seem to help the light seems to be the last thing that could be wrong but one plant is doing ok and the other is dried up roots look white to tan and healthy but the top looks like crap

 

[thelastpirate]

It's kinda hard to see the distance between the lights and the plant tops, but the lights are about 14" away. I DO have an overabundance of cool air moving in the room tho...I'd keep lowering them bit by bit until they show signs of heat stress, then back off a bit.

Theses are 400w MH lights:

 

[cookin]

this link has a light chart Light to plant distance charts / How far should the light be - Grasscity.com Forums

but thats just in terms of amount of light not heat, if your temp is 75 at plant level it is perfect and 19" is far enough i think

 

[Padishah]

thanks for the help ill look for other problems then

 

[LUDACRIS]

if it's a 400mh then the chart above says 19" is way too high.i would go for 12"-14" according to that data.

 

[tusseltussel]

i keep mine 16" away and dnt let it get closer than 12 and its fine and has bbe for years. as long as you have that air moving accross em you be cool

 

[richjames]

I think it really depends on the type of light and ballast ur usin, and how u control the cooling. I use a 400w hps without an air cooled hood and it is about 18in away. U can use the 'hand' method to chec temps from the light, but the best way to know for sure is to get ur thermometer at the top of the plants. If u do this, u can just keep checkin the temps and adjust ur lights as needed without worryin about burnin em.

 

[LUDACRIS]

surely thats going to send the thermometer sky high no???.
because its measuring the radiant temp coming from the lamp rather than the grow rooms ambient temp??.
just curious because i am running a 400hps without an air cooled hood(exept a 6" fan blowing on it)and i would like to find the perfect distance. i have had it at 12" for the last day but i am watching it closely.i have had it far to far away for the last 4 weeks.
CHEERS.

 

[Bamstone]

Depends on your setup. Using a cool tube and a 400w hps I routinely LST mine sideways letting the top buds get as close as 8 inches from the tube with no problem at all. They can go closer but they will bleach out and I don't like that.

 

[richjames]

surely thats going to send the thermometer sky high no???.
because its measuring the radiant temp coming from the lamp rather than the grow rooms ambient temp??.
just curious because i am running a 400hps without an air cooled hood(exept a 6" fan blowing on it)and i would like to find the perfect distance. i have had it at 12" for the last day but i am watching it closely.i have had it far to far away for the last 4 weeks.
CHEERS.

I'm talkin actual temps at plant level. U want it between 70-80. 76 is optimal, and anything over 85 is generally hurtin ur plant. To find the perfect distance, use the thermometer, or just do like ur doin. U'll find that sweet spot

 

[LUDACRIS]

I'm talkin actual temps at plant level. U want it between 70-80. 76 is optimal, and anything over 85 is generally hurtin ur plant. To find the perfect distance, use the thermometer, or just do like ur doin. U'll find that sweet spot

i understand.so if its above 76-80 should i move my lamp up to accomodate??
CHEERS.

 

[thelastpirate]

room dims are 23" x 30" x 6' temp in the room is 75°f i was wondering if i need a glass shield to block the UV i have a fan blowing accrossed the plants running dwc with very low nutes to see if the plant recovers tried normal and it didnt seem to help the light seems to be the last thing that could be wrong but one plant is doing ok and the other is dried up roots look white to tan and healthy but the top looks like crap

I doubt very seriously that you want to Block the UV. There are lots of threads here about how UV may increase THC production.

surely thats going to send the thermometer sky high no???.
because its measuring the radiant temp coming from the lamp rather than the grow rooms ambient temp??.
just curious because i am running a 400hps without an air cooled hood(exept a 6" fan blowing on it)and i would like to find the perfect distance. i have had it at 12" for the last day but i am watching it closely.i have had it far to far away for the last 4 weeks.
CHEERS.

Using a standard thermometer would measure the radiant heat, no doubt, and give totally inaccurate readings but if you use a "laser" type digital thermometer you'll get the actual temp of the plant.

 

[LUDACRIS]

I doubt very seriously that you want to Block the UV. There are lots of threads here about how UV may increase THC production.



Using a standard thermometer would measure the radiant heat, no doubt, and give totally inaccurate readings but if you use a "laser" type digital thermometer you'll get the actual temp of the plant.

thanks very much so basically using the basic thermometer idea mentioned above is not a good idea and are we talking about the type of laser temp gun that food standard inspectors use??.
and where do you point the laser(i.e. on the leaves or the top).
THANKS.

 

[richjames]

A digital thermometer shoud be used to keep an eye on the actual temps at or around plant level. The laser will tell u the acual temp of the plant, light, anything u point it at, which is good as well, but for overall temps, go with the dig therm.

 

[thelastpirate]

thanks very much so basically using the basic thermometer idea mentioned above is not a good idea and are we talking about the type of laser temp gun that food standard inspectors use??.
and where do you point the laser(i.e. on the leaves or the top).
THANKS.

It's really not a laser per se, it just uses a laser to aim it. They are infra red "no contact" thermometers. Here is one from harbor freight:

Harbor Freight Tools - Quality Tools at the Lowest Prices

I just tried mine, and under the 400w light I cannot see the laser dot. But I held it real close to the top and got a reading of 77degF. It will give you the actual surface temp of the leaf.

 

[LUDACRIS]

thanks thats very helpfull.
CRIS.