HPS parking lot lighting.

newgarageguyNovember 20, 2011

What happens when the wrong wattage lamp is installed in a HPS fixture? 150 watt lamp in a 250 watt fixture. Or vise versa?

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Ron Natalie

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A ballast that is too small for the lamp may not fire it.
A ballast that is too large may cause excessive heat and burn it out.

    Bookmark   November 21, 2011 at 6:30AM
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    Bookmark   November 21, 2011 at 8:13PM
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Most of us have no definitive answer since we never tried what you suggest. No experience. My answer would be only a guess. And I never tried it since it probably would ruin the lamp or the ballast or both. And I did not want to know badly enough to spend the money for those components. If you try it, please advise the results you observed.

    Bookmark   November 21, 2011 at 8:59PM
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I haven't tried it nor do I plan to. I am just curious. I have found fixtures with the wrong lamps in them after they have burned out but I have no idea how long they have been that way. It seems to not hurt the ballast. After relamping, the fixture appears to work correctly. I have asked an electrical engineer this question. Go figure, he couldn't answer.

    Bookmark   November 21, 2011 at 9:42PM
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Many of the newest ballasts have thermal overload to protect themselves.
What they do not protect against is over driving of the lamp they are connected to.

Once the discharge starts (in just about any discharge bulb of any type) the impedance of the bulb becomes very low (close to zero).
The ballast then limits the current flow to a safe level based on the bulb it is designed to operate with.

Use a smaller wattage bulb and the current is going to be higher than the bulb was designed for and bulb life may be short (possibly as short as a fractions of a second).

Older all magnetic type ballasts are more likely to suffer damage than newer electronic ones.

    Bookmark   November 22, 2011 at 9:55AM
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Thank you Brickeyee,
Have a happy Thanksgiving.

    Bookmark   November 22, 2011 at 9:07PM
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