Nice detail and clarity in these images. Always liked that early design and don't have an example in my collection. Early halide lamps were always relatively quite expensive and out of reach of my pocket money. Interesting how much the later design resemble the normal HP mercury vapour arc tube, although with blemish free quartz.

That blemish is just silica deposit from the burner's manufacturing process. It's presence as no impact on the lamp's key characteristics. Philips certainly went back to a basic design in its last HPI burner generation, made possible by improved material and production techniques. While the former enables a longer service life at higher power load and temperature, the latter reduced manufacturing tolerances, as necessary to achieve consistent light color and output. So, it may look like a basic HP burner but this is definitely much more advanced technology.

Despite its technological inferiority, I'm still fascinated by the earlier (i.e., gen 2) variant of the HPI burner. This presents a simple yet elegant solution to the limitations in material and manufacturing techniques that prevailed back in the 1960s. Although the mercury lamp filled with iodides of sodium, thallium and indium is a GE invention, this is really Jacobs's barrel burner design with a shortened arc length, developed at Philips, which made the technology truly competitive, so Philips's 2nd-gen HPI certainly holds a special place in the history of lighting. Personally, I remember first seeing them at my hometown's sport center when I was a kid, and for some reason that particular lamp shape and color struck me as highly unusual so, of course, I had to have one