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Metal Halide question

Discussion in 'Grow Room Design & Setup' started by Internode, Feb 3, 2012.


    Internode Well-Known Member

    I need to know if metal halide bulbs require cooling or venting from the hood? I am in a situation where the heat is actually needed to keep things warm during the on cycle but I am not sure if I can burn my bulb in an enclosed fixture without any air circulation....???

    400 Watt Powerhouse ballast
    400 Watt Hortilux Blue Metal Halide
    Hydrofarm Radiant 6 Reflector (ducted)

    smoke and coke

    smoke and coke Well-Known Member

    are you asking if you can run the bulb in your peticular hood without using ventilation? i am sure you can but maybe look up the manufacturer specs on your hood.

    i dont use a hood, just an open bulb but many types of fixtures that are fully enclosed with a glass lens and a 400watt MH or HPS that dont require cooling.

    i have my ventilation set on a timer and a thermostat so if either the timer of the thermostat calls for cooling it turns on the exhaust fan.

    the bulb itself doesnt require cooling, the reason for cooling is to cool the room for the plants.

    Internode Well-Known Member

    Yeah, I just need to know if the bulb has to have some sort of air circulation around it. Eye Hortilux website has a spec that says Max Temp 752 degrees and am not sure if that means how hot it gets or how hot its allowed to get. I have always ran open reflectors however, this bulbs instructions state to use an enclosed fixture and that is what I got but fails to specify if it needs to have circulation. Hydrofarm does not state if the bulb actually requires cooling....

    Good call on the thermostat, I think that is something I am gonna look into.

    smoke and coke

    smoke and coke Well-Known Member

    most HID bulbs specify use in an enclosed fixture only but alot of us dont use one.

    there are specially designed safety bulbs that you can use without an enclosure but they are very expensive.

    FootClan Well-Known Member

    In genernal its not a good idea to run enclosed glass hood with no air extraction However i have seen many people do it with 1000watters so i doubt your 400 would be a problem........if you can take the glass off the hood that would help alot.l

    rocknratm Well-Known Member

    You will have no problems. No need to actively vent it unless it gets too hot. As above said if its both cold and hot that are problematic then get something that only turns on a vent fan at a certain temp.

    What about at night when the lights are off? If you need it to keep heat during the day then what about night?

    Secondly, Ive heard that it lowers bulb life to use it w/out ventilation through the hood.
    more specifics/>>>?????

    rocknratm Well-Known Member

    I wouldnt take the glass off either. More heat down imo.
    Also you will have more hot spot problems or more potential to burn the tops of plants. So set height carefully

    FootClan Well-Known Member

    I disagree i love taking the glass off if anything it filter less light with no glass.. Plus if you use a MH bulb with no glass you get more UVB rays from the bulb..... I only put my glass in when theres heat issues and i need to activily cool my light........ If you have no aircooling in the hood theres no reason for the glass.....The glass will make it more hot because it keeps the heat in the hood making it harder to disapate.......

    roidrage152 Active Member

    agree with the last guy if ur not air cooling remove the glass. The glass definitly reduces light.

    grandaddypurped Active Member

    :leaf:I'm in the same position as winters here are very frigid. I do not circulate any air to the bulbs (just what's being moved throughout the room from the osc. fans) & I leave the glass on (by choice). I don't think you could go wrong either way (glass on or off), but regardless it WILL NOT bother your bulb/hood/etc if you don't ventilate...:peace:
    Brick Top

    Brick Top New Member

    Maybe I misunderstood things, but, if the heat from the light is needed to maintain adequate temperatures in the grow room, why not make the most of it, why not go for maximum efficiency? If I understand things right you have a glass enclosed hood and you rely on what heat radiates through the reflective hood, glass and is carried by convection out of the hood vents. Is that an accurate portrayal?

    If so, why not purchase a somewhat low CFM fan and enough ducting to go from whichever side of the reflective hood you pick to exhaust down to the floor? Any heat that now leaves the light through convection or radiates through goes straight up and then the temperature will slowly build from the highest point down to the lowest.

    Why not instead somewhat duplicate the workings of a furnace? Use a fairly low CFM fan and a piece of duct-work to exhaust the freshly heated air at floor level, the coldest level of the grow room? Convection will carry it upwards more evenly heating the grow room from bottom up and when it reaches the reflective hood it will be drawn through, reheated, and again exhausted at the lowest/coldest part of the room.

    That or lose the glass and improve the light quality while at the same time maximizing downward heat radiation, which will not nearly equal circulating the heated air in the most efficient manner, to the lowest level of the grow room, but it would still increase efficiency. Either way you have improved your temperature maintaining problems, removed, or at least greatly reduced any risk of an overheated bulb and improved your light quality.
    smoke and coke

    smoke and coke Well-Known Member

    i am not sure how much it lowers the bulb life when there is an endless number of street lights, parking lot lights, wall packs, and warehouse lights etc. using enclosed fixtures with HID bulbs. even the ballast is enclosed in the same fixture and you dont see ventilation run to those lights.
    smoke and coke

    smoke and coke Well-Known Member

    if the glass was removed from the hood, just a small fan blowing at the bulb would blow the heat around the room and even the temp. throughout the room.

    mrmadcow Well-Known Member

    but those fixtures are designed to run w/out a duct and fan.they have openings at top and bottom and let the heat create convection to move the air/heat out.
    it may not hurt to run without a fan but I would at least add a small PC fan & think Bricktop's suggestion would be best.
    smoke and coke

    smoke and coke Well-Known Member

    i just installed 6 - 1000watt wall packes that are completley sealed. not a vent hole anywhere. i suppose for the most part the only thing that may be designed different is the temp. rating of the wires inside the light.

    Internode Well-Known Member

    Thanks everyone, 24 hours without running my exhaust blower and no problems. 74 degrees at canopy, 50% humidity, but still having problems with plants being droopy after 18 hours of light on. They are perky early on but in the last hours of the light period start looking bummed out. I raised my hood thinking they may be getting over exposed to PAR, we shall see... I am currently at 36" above the top most area of plant material....
    smoke and coke

    smoke and coke Well-Known Member

    did you disconnect the ducting from the side of the hood? may be a good idea if your not going to run the fan at all.

    Internode Well-Known Member

    I vent through my hood so one side is always open. I am rather experienced but have upgraded and rebuilt my room from 250 watt setup to the new 400. I never had exhaust before so I figured the upgrades would make the plants happier but am having more problems than ever before. My last yield was 7.5 oz dry Master Kush from my 250 watt scrog and an early harvest due to mold hence the exhaust now. No problems with veg before and temps were higher.... It may be a strain issue. Any experiences out there with Pineapple Chunk and what it likes?

    cannabineer Ursus marijanus

    That was my thought as well ... it's how I would do it. Win/win. cn

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