new guy need lighting help

if someone were to use 2 600 watt hids in a large room (25' x 15') over a raised platform 4' x 4' in diameter to do 10 plants what is the highest the lights could be above the plants and still get good growth? will be starting with 66000 lumens mh conversion bulbs then switching to 95000 lumens hps to flower. they are not cooled lights and i'm concerned with over heating. how warm can seedlings and plants be safely? the room is vented to the outside , but temps are still higher than i would like on the platform . thanks for any info you can supply me with.

for your seedlings a would NOT use hps/mh , instead try some cfls . as far as height , on a uncooled light i would like to say about 15"-18". i am not that sure ,but i sure wouldnt get any closer than that.

and welcome to RIU by the way . this place rocks!!!!

i've been lurking around here alot and finally got up the nerve to join up. i was hoping i could start them out with the lights high having 2 lights but i'm just not sure how far away or how much heat they can stand.

2beanklm said:

i've been lurking around here alot and finally got up the nerve to join up. i was hoping i could start them out with the lights high having 2 lights but i'm just not sure how far away or how much heat they can stand.

Click to expand...

Rule of thumb for light distance is if you cant hold your hand at the top of the plant without it getting uncomfortably hot then the light is too close. An Ideal temp for the room would be between 26-28C, sorry you will have to convert for F, thinks its about 78F but not sure.
The advise about not using MH lights to start is sound, but if you have no choice other than MH to start with you can shield the babies so that they wont receive so much intense light, some meshing can do this, you can even buy shield adapters for you lights also, believe they are called diffusers.

For the vegetation period use CFL and forget the high intensity lights until they get 12in tall or if they are autos, then it don't matter You do not need to put the lights too close because you will want to get the seedlings to stretch a little bit for good stem development. With your seedlings, the room should not be over 87 degrees at any time. Humidity needs to be around 30% for optimum growth at this stage of their life. During moderate veg growth an increase in humidity can be allowed up to 50% but anymore will promote fungi and mold development. My professional advice is to allow the plants to reach a height of 1ft before placing any heavy lighting to them. And then it is best NOT to try and get as close as some suggest. Start about 8 inches from the top of the plant and adjust towards the plant based on their growth, you'll want to maintain a height to light ratio of about 7 inches from the top of the plant at all times after that. Also, you'll need to have a good ventilation set up as those HID bulbs will create a lot of heat that needs to be managed.

Peace,
Autoflowerchild

Here's a good light spectrum chart for growth you'll find helpful my friend.

Peace..Autoflowerchild

80F maximum..I'm thinking 2 1/2 ft., tops....

Another problem with starting your seedlings with an MH is because of the distance from the light, the seedling will stretch. Heatwise for your HPS lights, it also depends on your airflow - I have great airflow in my flowering room, so I am able to keep my 400w HPS about six inches above my plants, where someone else may have to go twelve inches or more. So your best bet, is to do the hand test, and do what works for you.

JoeCa1i said:

80F maximum..I'm thinking 2 1/2 ft., tops....

Click to expand...

80 degrees "maximum" would be difficult to maintain and will depend on a variety of environmental conditions that should be controlled. By an amateur grower (no offense) this is not always gonna happen right off the bat, it didn't with me too. I stated 87 MAX due to variables in room ventilation, ambient temp and the lights he stated he will be using and that will affect the room temp. In a 12x12 room a single MH bulb can raise the ambient temp 25 degrees, therefore requiring a ventilation system that is working all of the time so the plants won't suffocate with the heat. And yes, plants can suffocate when the heat gets beyond their genetic threshold of tolerance. So, 87 degrees max is a more realistic temp than trying to maintain a constant 80 given what the room/space is used for. Provided ventilation is good your optimum grow room temp should around 85 degrees with a nice circulating breeze to lower the wind chill effect on the plant's surface just as in "people"weather conditions.

Peace,
Autoflowerchild

Thanks everyone. the mesh is a good idea. guess i'll try starting under just one mh and see what happens. the room temp is around 72 degrees but the temp at the platform where the plants will be is 85-87 with the lights 3 feet up. i was hoping having 2 lights for a 4x4 area would allow me to run them a bit higher than just 1 light.

2beanklm said:

Thanks everyone. the mesh is a good idea. guess i'll try starting under just one mh and see what happens. the room temp is around 72 degrees but the temp at the platform where the plants will be is 85-87 with the lights 3 feet up. i was hoping having 2 lights for a 4x4 area would allow me to run them a bit higher than just 1 light.

Click to expand...

You should have a fan to circulate the air, if you havn't already, should help stabilize the temp of the room.