Hi!

I'd love to know all about HPS lamp design. I own two HPS wall packs, a 35W and 70W, and I have some spare lamps for both.

I have the original bulb from my 35W wall pack, made in 1996. It's a GE LU35. I have a spare OEM Philips bulb, which has a more narrow arc tube compared to the LU35 and feels cheaper.

The LU35 has silver ends on the arc tube, and the arc tube is quite thick.

I have a nice Sylvania 70W lamp, which feels very robust and doesn't have the silver ends on the arc tube. I also have two coated GE 70W lamps.

I recently bought three NOS GE Lucalox 35W lamps, which appear to be pretty vintage. The box has a description about an external amalgam reservoir, which none of my other lamps have.

What are some of the differences between lamps with an external amalgam reservoir, and those with the amalgam within the arc tube? Are lamps with an external reservoir usually older lamps?

Finally, what are some operating characteristics and expected life between brands of these older lamps and newer lamps, and lamps with an external amalgam reservoir? Do certain lamps warm up with different colors on startup, and do lamps with the external reservoir warm up any slower or faster, or behave any different? It's all interesting to me and how each manufacturer designed their lamps and arc tubes, and what designs became the most reliable. It's also interesting to me how different lamps might be slightly different in the colors they produce while striking and warming up.

Hi HPS4Ever425120,

I haven't seen any replies to your post, and while I am certainly not an expert on lamp design and construction, I'll share what I've noticed in collecting over the years.
Older HPS lamps (at least GE/Westinghouse) used a large pinch seal tube arrangement for the external amalgam reservoir, while newer lamps seems to have incorporated the amalgam reservoir internally directly into the electrode assembly and isn't really noticeable anymore.
Older HPS lamps also used a metallic strip around each end of the arc tube ends for sealing (I believe it was niobium, which has similar expansion/contraction rates as the alumina).  Newer designs lack these strips, presumably as brazing of the alumina ceramic arc tube with the alumina cap around the electrode assembly was perfected.
I haven't noticed any other noticeable differences between older and newer style lamps, their electrical operating characteristics should be the same regardless of vintage. I have noticed various differences in colour of HPS lamps, ranging from a nice pinkish peach to a yellow-orange, but the lamps were all in luminaires that I could never ascertain the make or model of the bulb due to the diffuser, so I cannot comment on what exactly made the difference.

I hope this helps!

IIRC the mercury content of HPS lamps has changed over the years, from what I remember the older HPS lamp would have a bluish startup due to the increase mercury while the newer low mercury lamps startup white from the xenon fill gas.

I believe when fully run up, the older ones had a more golden yellow appearance while the newer ones are more yellow orange.

@joseph_125 — I've actually noticed exactly that. A few local ski resorts still maintain their HPS installs, and newer lamps have a far lighter hue to them (no "golden bask" as with older lamps). And all of the new lamps with their more muted color are Chinese in origin, also. USA and even Mexican-made lamps from the likes of late Osram-Sylvania and even GE out of Hungary made lamps with the "proper" golden glow most of us have been accustomed to seeing.