Do you have a low pressure sodium lamp where the outer glass envelope is cracked… if so do you wonder if it’s still functional? Well I have some answers based on experience with one of my bulbs.

When a SOX’s envelope is cracked, the lamp will lose vacuum. When this occurs, the lamp’s getter (the metallic coating at the base) will suddenly turn white. Having a vacuum is necessary in how the lamps operate, as without it the lamp supposedly will not retain heat properly and warm up completely; with some claiming it will stay stuck in the pink phase. I had someone state my defective lamp was a loss, but I couldn’t get a straight answer, so I put mine to the test.

My lamp is 135W, and was cracked in the previous owner’s storage. I hooked it up to a legit Advance SOX ballast and turned it on. From my observations, the lamp warmed up to about 70% it’s rated output, with the sodium (for the most part) vaporizing and the lamp turned its distinctive yellow hue. Although this seems promising, the lamp took at least 20 minutes to get to this stage, the outer glass was extremely hot, and one side of the U-bend was more transparent than the other. After 30 minutes I turned it off.

In conclusion, a SOX lamp with a vacuum leak isn’t a completely a total loss. The lamp is still functional to some degree but performance is hindered. Even though my experiment worked better than I expected I don’t recommend it, especially in regular use.
 

You can run up a jacketless SOX tube, like I did on my ‘Frankenstein 18 watt SO’, but you have to batter the tube with a few more amps!