HID lamps that are rated for outdoor use often market themselves as having borosilicate outer envelopes. This makes it less likely to fail in the case of a drop of water falling on them while they are hot.

If you are well-versed in glass language, you know that "borosilicate" doesn't mean anything when it comes to thermal expansion coefficient. Commonly there are borosilicates around 3.3 CTE and there are borosilicates around 5 CTE. The ~3.3 stuff needs tungsten wire to make a seal (seal looks yellow), and the ~5 stuff needs Kovar wire (seal looks grey-green). I have the following questions:

---

1) Is 3.3 Ever Used?
Every borosilicate envelope I have ever seen has featured Kovar seals, signifying that ~5 CTE glass is used. Is there ever a situation where they would use ~3.3 CTE borosilicate with tungsten seals? I have yet to see a tungsten seal in an outer envelope, though I know they were used in quartz graded seals for early HPMV lamps.

2) Alloys for 3.3 Borosilicate?
Nickel-iron controlled expansion alloys exist anywhere from ~0 CTE (Super Invar), to at least ~9 CTE (Dumet), so why is there no nickel-iron alloy that has ~3.3 CTE for borosilicate? Tungsten isn't super easy to work with because it is so brittle, and it doesn't even match that well in terms of CTE.

---

Thanks!

HID lamps that are rated for outdoor use often market themselves as having borosilicate outer envelopes. This makes it less likely to fail in the case of a drop of water falling on them while they are hot.

If you are well-versed in glass language, you know that "borosilicate" doesn't mean anything when it comes to thermal expansion coefficient. Commonly there are borosilicates around 3.3 CTE and there are borosilicates around 5 CTE. The ~3.3 stuff needs tungsten wire to make a seal (seal looks yellow), and the ~5 stuff needs Kovar wire (seal looks grey-green). I have the following questions:

---

1) Is 3.3 Ever Used?
Every borosilicate envelope I have ever seen has featured Kovar seals, signifying that ~5 CTE glass is used. Is there ever a situation where they would use ~3.3 CTE borosilicate with tungsten seals? I have yet to see a tungsten seal in an outer envelope, though I know they were used in quartz graded seals for early HPMV lamps.

2) Alloys for 3.3 Borosilicate?
Nickel-iron controlled expansion alloys exist anywhere from ~0 CTE (Super Invar), to at least ~9 CTE (Dumet), so why is there no nickel-iron alloy that has ~3.3 CTE for borosilicate? Tungsten isn't super easy to work with because it is so brittle, and it doesn't even match that well in terms of CTE.

---

Thanks!

I was under the impression that most if not all hard glass lamps employ tungsten feed through wires? (hence why they are heavy and thick, unlike the thin dumet wire of soft glass lamps)

certainly seen plenty that show a Yellow tint to them, for example:

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-231306

https://www.lighting-gallery.net/gallery/displayimage.php?pos=-223234


as for hardness of glass used, it certainly varies, US and Japanese lamps often use cheaper Softer hard glass then European hard glass lamps for example

and in some very demanding applications like Hard Glass Halogen lamps, you will find aluminosilicate bulbs instead


https://www.lighting-gallery.net/gallery/displayimage.php?pos=-53390