On Mon, 15 Oct 2012 12:33:46 +0000 (UTC),
(Andrew Gabriel) wrote:

The shape is a standard equi-thermal bulb (the shape you end
up with if you want the bulb to be similar temperature all
around the enclosed short arc tube, ignoring convection heating).

I used to be interested in different shaped light bulbs when I was
young. It's a shame I lost interest as I grew up. It must be an
interesting industry to work in.

I've never seen a BC high pressure sodium lamp, or BC on any
equi-thermal bulb, because a BC lampholder can only support
that weight and size of lamp when hanging cap-up. It was used
for some early mercury vapour lamps with more conventional
(GLS/pear-shaped) lamps, for use in cap-up fittings, including
self-ballasted ones with internal filament ballasts, but yours
has an external ballast (and no external ignitor, at least, you
didn't mention one).

I have had a closer look. There is something printed on the bulb but
all I can make out is "Phillips"; the rest is too faded to see. It
seems it is not a BC cap but actually has pins at right angles, a bit
like a car brake light. I've taken a photo for you to see. You may be
able to see a little of what is inside the glass, if that helps
identify it?

As for an ignitor, I have no idea what one of those is so I don't know
if it has one. There seems to be a patch on the "ballast", if I am
using that word correctly, as if a label used to be there but it is
long gone, so I can't tell you more I'm afraid.

The capacitor label, not the best photo, sorry, says it includes a
resistor and a fuse.

The lamp:
http://tinypic.com/r/2ni0h1k/6

The bulb:
http://tinypic.com/r/2qbgl6s/6

and
http://tinypic.com/r/w9ean7/6

ballast:
http://tinypic.com/r/p9mhh/6

capacitor:
http://tinypic.com/r/ieqyyc/6

I don't know if any of those help at all?

Thanks.