I have a coach lantern-style street fixture on my property that needs a bulb. It currently has a 100w LU100 and it may...MAY...be the wrong size.
What happened to the original failed Lamp?
I am wondering why you might feel the wrong wattage Lamp had been used originally.
If the original Lamp was "Cycling" on and off for awhile, and gradually cycled off faster and faster until it just would not fully start (only had a bluish light output, then goes out within 30 seconds), this is normal end of life results for the HPS Lamp.
If it will not start now, but started and ran OK just a few days before, suspect the Ignitor.
If the Ballast windings are charred, suspect either incorrect Lamp wattage, failed capacitor, or both.
If you use a lower wattage Lamp on a higher wattage Ballast, it will fail sooner.
The cross over piont is at the 150 watt HPS - as there are 2 types here; 55 Volt and 100 Volt Lamps.
Use the wrong ones here and you will know very soon that there was a mismatching conflict!
Also using a Lamp / Ballast match where the values are very different (like 175 watt Lamp on a 400 watt Ballast, or vise verse) will bring sudden doom!