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can i use a standard MHbulb with a HPS ballast


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#1 big#bud

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Posted 16 July 2007 - 03:50 PM

hi ive just been reeding this

I've found either a single metal halide or high pressure sodium light system works nearly as good as a dual system. So if you only have one or the other don't worry, it will work just fine. You can't use a standard hps bulb in a mh fixture, but you can use a mh bulb in a hps fixture of the same wattage. I didn't think this was possible till several months ago when someone I trust told me it was possible. So I decided to try using a 400 watt mh bulb in a 400 watt hps fixture. The plants are growing as well as they did under the mh bulb in a mh fixture. The bulb hasn't had to be replaced and the ballast runs as cool as it does with a hps bulb

is it true ?
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#2 Heavy Horse

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Posted 16 July 2007 - 04:15 PM

Sometimes, my Powerplant ballast will, my cheapo Screwfix Lowbay conversion wont. But even if your ballast wont support both, you can buy an MH lamp which will run on the "wrong" ballast...if that makes sense :yahoo:
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#3 scraglor

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Posted 16 July 2007 - 04:25 PM

the high voltage pulse from the ignitor in an hps ballast can damage the electrodes in a MH lamp, shortening the life of it, also MH lamps require a cleaner AC waveform than is provided from an HPS ballasts, and run at slightly different voltages, these factors affect the lifespan of the MH lamp when run in an HPS ballast, but you should be replacing your lamps before any of this happens anyway, due to loss of light quality.

an HPS wont run in a MH ballast, because there's no ignitor in the circuit
i'm not arguing, i'm just explaining why i'm right


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#4 RePtOiD

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Posted 16 July 2007 - 04:38 PM

What about digital ballasts are they excluded from this rule?

#5 Davey Jones

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Posted 16 July 2007 - 08:19 PM

What about digital ballasts are they excluded from this rule?



Good question the lamps are the same so the ballast does the same job so I would guess it will work, I was told this some time ago but my ballast is for both so I have never tried it obviously its true, the MH doesn't need an ignitor but it still gets a HV spike from the ballast like a fluorescent,

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#6 _friendly electrician_

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Posted 16 July 2007 - 08:25 PM

the high voltage pulse from the ignitor in an hps ballast can damage the electrodes in a MH lamp, shortening the life of it, also MH lamps require a cleaner AC waveform than is provided from an HPS ballasts, and run at slightly different voltages, these factors affect the lifespan of the MH lamp when run in an HPS ballast, but you should be replacing your lamps before any of this happens anyway, due to loss of light quality.

an HPS wont run in a MH ballast, because there's no ignitor in the circuit


MH control gear does include an ignitor, and will fire sodiums.
10 ignitors are ok for sodium, but not really good for halides. There 3 wire items, and inject voltage into the lamp wire based on ballast voltage, which will change once the bulb fires.

25 ignitors fire both sodium&halides. 3 wires again, but this time the lamp wire goes in on one connection, and out on another. the 3rd being neutral.

Both make about 4.7kv but i 'think' the halide version timely chops the ballast currant, and as such has a greater energy reserve. There no nonsence anyway. a short pause then they fire in one go. sodiums are trying from cold and briefly keep trying after ignition.


older lamps had in-built ignitors. it seemed the sodium market switched over to electronic starters years before the mh market started too, and even then it was slow. Im sure even now you can get large mh lamps with internal ignitors. only 70w sodiums seem to self start now though.


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