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-   -   HPS (High Pressure Sodium) yard light (http://www.diychatroom.com/f18/hps-high-pressure-sodium-yard-light-160325/)

rjniles 10-16-2012 08:22 PM

HPS (High Pressure Sodium) yard light
 
I installed a HPS yard light about 5 years. It was a 70 watt unit. The light was more than I needed so I installed a 35 watt lamp in the fixture. It has worked fine untill about a month ago when it started cycling (? Bad lamp) . I installed the 70 watt lamp that came with the fixture and it worked fine. Bought a new 35 watt lamp. This lamp is cycling. Is this a problem with fixture or is the new lamp defective?

brric 10-16-2012 09:26 PM

I could be wrong but my understanding has been that the lamp wattage must match the internals of the fixture.

AllanJ 10-16-2012 09:38 PM

Correct. Using the wrong lamp can damage either the lamp or the ballast or both.

The purpose of the ballast is to limit the current flowing through the lamp. A high pressure sodium lamp (also a mercury lamp and a metal halide lamp), as it warms up, has its internal resistance go down. Simply applying voltage to the lamp sufficient to strike it will result in an ever increasing current which will result in the lamp's self destruction.

With the wrong lamp in the fixture, the ballast and lamp may reach an equilibrium current that is excessive for the lamp causing it to burn out, or reaches an equilibrium current that is insufficient causing the lamp to extinguish and perhaps restrike again and repeat the cycle which can wear out the ballast.

deverson 10-16-2012 10:19 PM

You would probably damage the ignitor before burning up the ballast. You have to keep the same wattage lamp that the ballast is designed for. I put labels on fixtures at work but some people cannot or will not read them.

rjniles 10-17-2012 09:26 AM

Thanks to all who educated me. I have reinstalled the 70 watt lamp and is working fine.

Oso954 10-17-2012 11:41 AM

The fixtures and lamps come labeled with an ANSI ballast code.
A 70W HPS is a S62 ballast, the 35W is a S76.
All you have to do is match the ballast codes.


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