Originally Posted by funkjosh
can someone please tell me why a high pressure sodium bulb will not work in fixture (designed for high pressure bulbs) but a compact fluorescent will?
Most common failure with HPS if not replace the lamp fast engouh is the starter or ingitor which they will send high voltage pulse to get the arc started then the ballast will regulate the voltage/current to proper spec.
There one more important part make sure if you going to replace the HPS lamp make sure it will match the ballast this is true for 150 watt verison due there is two verison it used one is 55 volt arc tube and second verison have 100 volt arc tube both are not interchangeable.
The typical open circuit voltage is 120 volt range for 55 volt arc tube verison ( under 150 watts ) while the larger one it will be about 250 to 400 volts depending on the wattage so that the differnce on that.
You may find the ingitor in big box store but kinda hard to find them but electrical supply centre even lighting centre may have it on hand otherwise they can order ya one. But make sure you mention the correct bulb wattage or bring the old one in to match it up.
But one warning with ingitors when you replace them make sure keep the power off and also watch the connection very carefull it don't take much to get it screw up.