This seems to be mostly a US problem, in other Europe most of the time clear lamps are tubular and diffused lamps are elliptical. However particularly with low wattage and retrofit lamps, this does not seem to be the case in the US.

For example, most clear 360W HPS retrofit lamps are BT-37 shaped, which matches their MV counterparts. But why not make them tubular (like normal 400W HPS)? The envelope is clear anyway, making it bulb shaped doesn't make a difference.

And for smaller regular HPS wattages this is still the case, most 35-150W HPS lamps are not tubular in the US. Often they are BT, E, or ED shape. Is it to reduce the surface temperature of the envelope?

And of course out larger wattages (250-1000W) are almost never actually tubular but rather a strange elongated elliptical-ish shape. How did this shape come about? Why not just use plain tubular like the rest of the world?

Now I know for things like MV and MH (which are usually nitrogen filled in the outer envelope), having a tubular envelope can sometimes restrict their use to vertical only so the envelope doesn't end up melting. But I haven't heard of this happening with HPS before.

Anybody have any ideas?