HPS Restrike
Because this lamp does not use an internal ignitor, the external electronic ignitor used with it here enables it to restrike without cooling down fully. This means that, for a momentary supply interruption, this lamp is out for no more than 10 seconds and when it restrikes, it is at almost full brightness again straight away.
Here's the first video
Click here for the first video (Realvideo) if you don't want to use the mp4 version. The video starts a couple of seconds before power is removed. When power is removed, it is returned straight away (an interruption of 2 or 3 secs). You can see that as soon as the arc tube is just below 'red' heat, the ignitor voltage is enough (about 4kV) to create an unstable arc in the tube. This lasts for 2 or 3 seconds before the lamp restrikes.
Here's the second video
Click here for the second video (Realvideo) if you don't want to use the mp4 version. This starts just as the unstable arc is formed. It's running in slow motion- the righthand most set of digits is PAL frames ie 1/25th of a second per count (time display on Realvideo version only). Watch how the arc appears to curl and rotate round the tube! In real life this happens in about 2 seconds.
Here's the third video
Click here for the third video (Realvideo) if you don't want to use the mp4 version. This is a closeup of the unstable arc, in slow-mo as before. You can get a better look at how it dances round the arc tube before the restrike.