Discharge lamps fail in a number of ways. One of the most common behaviors of dying high-pressure lamps (Son / Halide) is to strike, run up then extinguish once almost at full brightness. Give it 10 minutes or so to cool down and it`ll do it all over again. Or they just won`t strike at all, maybe just glimmering round the edges. Low pressure sodium lamps that strike might stay in the red neon phase, flickering like a duff flourescent tube. Or they`ll never fully run up staying red or deep orange. A totally dead one again will not strike at all other than a faint pink glow round the electrodes. The one over the road`s like that right now - I hope they don`t replace it till early next year. It`ll make a change not to have its orange glare cast all over my festive lights display during December!
Most HID fixtures need three things (besides the lamp and lamp-holder). The ballast, the ignitor and the PFC capacitor. They`ll work without the cap but it`s nice to have it there. Low pressure SOX lamp ballasts sometimes have the ignitor built in, epecially the old ones - mine does. Mercury lamps don`t need ignitors, and low wattage ones will actually work with the appropriate flourescent tube ballasts. A 50 watt one I have here runs just fine with the ballast of a 5 foot T12 tube though it`s probably best to stick with proper mercury ballasts incase the lamp ends up over or under-run which could damage it.
You know it already but the excellent lamptech.co.uk has a wealth of technical info about all kinds of discharge lighting including failure modes for some of them, and I know James plans to have such info avaliable for all common types eventually.
Probably the best place to find old fixtures is the council`s streetlighting depot in your town. That light they replaced had to go somewhere, and often there are piles of them just sitting there rusting. Find out where it is, pay them a visit and ask nicely - you never know. They might let you walk off with a few used fixtures and lamps that would otherwise become landfill.
Failing that, wander round the `Net and look for British Streetlighting enthusiast web sites - there are a fair few out there. One of them is Bob Cookson`s -
http://www.cooksonr.freeserve.co.uk and several are linked from lamptech.co.uk too. Those guys might know where you could buy some for next to nothing, and may even have a spare lamp or ballast lying around that they might be willing to part with.
Don`t even start looking for brand new ones. They cost big £££s and streetlight heads are not easy to purchase in one off quantities anyway. Radiospares sell an assortment of SON, SOX and Halide fixtures, ballasts, ignitors and lamps but they are all seriously spendy.
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LPS fixtures, buying used?
Linear Mode
