HPS too hot?

Discussion in 'Growing Marijuana Indoors' started by ksac, Jun 15, 2006.

  1. <meta http-equiv="CONTENT-TYPE" content="text/html; charset=utf-8"><title></title><meta name="GENERATOR" content="OpenOffice.org 2.0 (Linux)"><meta name="AUTHOR" content="Garry"><meta name="CREATED" content="20060614;18320600"><meta name="CHANGED" content="16010101;0"> \t \t \t \t \t \t<style type="text/css"> \t \t</style> I've been looking into buying a 400W HPS light for my 3'x5' grow space (closet) with 5' of vertical space. Heat and limited vertical space makes me wary of HID lights. Now here's my dilemma... I do not have the money nor permission to be drilling holes and installing a good ventilation system. I currently have a fan mounted the the top back corner that runs constantly, indirectly (fan points toward back edge of opposite wall) moving air in the grow space. The door of the closet is left open for extended periods during the lights-on cycle and closed during lights-out. This has been sufficient for my fluoro setup. The closet stays fairly warm during summer time getting as hot as 90 F. Is a HPS light going to create too much heat?

    Second, my height limitations. Most advice I've seen recommends 2-3 ft between light and plant, which gives me 2-3 ft of possible vertical growth. I plan on trying LST of scrog. LST is my fist choice but I will plan for scrog if it is more practicable for my situation. Will I be wasting my time and money on a HPS light? Is it feasible to get descent yields with my grow space?
  2. Yes it will get too warm if your fluros reach 90 degrees already.

    No HPS & LST go together just fine.

    Descent grow? For a drugdealer no, but your average Joe Growittosmoke absolutely.

    But if you want to use serious power in the box (400W) you will need some serious ventilation.
    If the fluros push the temps in the 90s already I bet you need at least a few hundred CFM of fans to cool the box with the HPS.
  3. The temp reaches 90 during the day on hot days. I figure I could run the lights during the night when the temps are closer to 60-70. How much heat can I expect from a 400W HPS with reflector? Is it harmful to the plant for the dark periods to be warmer than the day periods?
  4. A 400w HPS will put out quite a bit more heat than your flouro setup, your best bet would be to build a cabinet so you can more directly control ventilation.

    1 - 2 feet is just fine for light distance.

    Also consider moving your fan to blow in between the light and plants, the breeze will help strengthen your plants and keep them much cooler. You will still need an exhaust fan though. Don't worry about closing the door during veg if temps are running too hot.

    I grow in roughly the same space as you in a closet, if you can afford the light and all accompaniments your yeild will definitely thank you.

    [Edit] Forgot to add this.

    Warmer dark periods are more beneficial from everything I've heard, I've never seen any noticable increase of growth or health on my plants though.
  5. I'm not sure what you mean by building a cabinet to control ventilation. Could you elaborate? I'm currently devising a venting solution where I'll be venting directly outside. What type of exhaust fan should I be looking for? A bathroom exhaust fan? How often and for how long will I need to exhaust? Some info on cost and effectiveness of controlling exhaust with thermostat would be helpful. Thanks.
  6. i have a 3 foot by 4 ft by 18 inch box and i have it in a closet. i have a 250 hps in there and the temp was up to 110 in there with the door closed!!! i keep the door open and a fan int he box with vent holes in the box and now its down to 84 and i get decent size yields. so to answer your question yes they r very hot! u also need sunglasses to go in there!
  7. Uhhhm. You sounds confused. You confused me too there for a bit...

    If you run the HPS at night, then for the plant night will become day. And that HPS will push the temps inside the box far beyond 60-70 degrees. I guess if its 90 in the dark during the day, it wil be about 90 as well in the light during the night.

    If you really want to know how much heat that HPS will produce FEEL IT.
    Turn it on for 10,20 maybe 30 minutes let the lamp heat up.
    Then inspect using your skin. You will feel the heat radiation from this lamp at a few feet distance. Feel the fluro's too so you can compare. Try the television, your computer any electronics and feel their heat, check the Wattage and compare.

    remember this :


    If you like calculating then assume > 90% of 400W turned into heat. 360W of heating.
    That's 360 joules per second, enough to heat 360 grams by 1 degree Celcius in 1 second time.
    Or 36 grams heated up by 10 degrees C in 1 sec
    or 1 kilo heated by 1 C in about 3 seconds.

    I have a grow box inside a normal room. A mere 108W fluro grow. In my case the box with the lights on is 15 degrees C hotter then the room temp outside the box. That's +27 degrees Fahrenheit.

    Lucky me, the first heat wave in years strikes where I live and temps in the room go WAY PAST 110F.
    Temps inside the box is anybodies guess but it must have been WAY past 130F.

    Result : dead fluro tube, dead ballast in another fixture and a dead timer.

    In my case, the plant proved more resilient then the electronics, for it took the pain with grace and lives on.
    Good thing it had only 1 more week of flowering to go so its not a big loss for me.

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