great clear photographs, work of art seeing these lit

Thats unusual for any low pressure sodium lamp, I`ve seen cathode flare, but this only lasts a few seconds, but never seen this.

This lasted right until the middle of the lamp had completely run up, but gradually drowned out by the sodium radiation. Tomorrow I will take into work and measure the chemical composition of the gas discharge to see what's there. Maybe you are right about it coming from the cathode, perhaps it was contaminated with something.

Amazing pic!

Another wonderful pic. Beautiful lamps

What a gorgeous photo! I do love watching my SLI/H lamps warm up. Not yet found a GEC 60w or 140w version.

Mgod amazing picture I want to play with my SLI/H lamps now

is it a new lamp thats probably carbon dioxide the same thing that happens such as the blue flare from new sox lamps. i once had a osram 135w that had blue halfway up one side of the dt on startup

Awesome pic! This could be hung on a wall as art!
I'd love to find one of those SLI/H lamps

Thanks! I have it on my desktop at work I think you are right John, I took it to work to measure the gas emission spectrum and it didn't do it again. I was surprised to find that there is virtually no neon in the GEC SLI's, they are filled with argon and xenon!

How on earth do you measure such things James surely you have to puncture the lamp?

@Kev: I would assume he has a spectrometer or something like that 'reads' the spectrum it puts out when on?

Probably some sort of diffraction grating.

SLI/H lamps are always a joy to watch warm up, especially the GEC version!

Right, we have a spectrometer with a small optical fibre cable which you can point at certain regions of the discharge to analyse the colours of the ionised filling. It's used together with some software we wrote that detects the wavelength of each spectral line, then looks it up in a database of the elements, and you can instantly see which elements are inside. Very useful for inspecting competitors lamps without destroying them, years ago at the lighting exhibitions it was not unusual to find lamp engineers walking around with pocket spectrometers and trying to discretely aim them at some new HID lamp on show and find out the chemical filling before they were launched for sale There also used to be a great hotel in Eindhoven directly opposite the Philips labs - and more than a few times engineers from competitors were known to book a room there, take with them a good telescope and a spectrometer, and point it through the windows of the labs to find out what new elements Philips was researching in its lamps! No more fun these days with LED, the technology is all too often the same and far too simple, or at the microscopic level and you can't investigate anything outside the labs.