Hi,
You are correct in assuming this would be a collectible bulb, especially for one interested in antique bulbs. A lot of antique bulbs that surface were manufactured in the early years of the 20th century, and while old, many are fairly common. Your bulb, on the other hand, is earlier, possibly the early 1890's, and therefore more rare.
The filament is indeed carbon and is in one of the earliest filament configurations commonly known as a "hairpin" filament. It is possible to find bulbs well into the 1890's and even early 1900's with hairpin filaments, but in the later years these were mostly for 50 or 55 volt lamps. Your bulb appears to be earlier because in the picture you supplied showing the bottom of the Thomson-Houston base one can clearly see a red fiber type material used as the insulation between the center threaded terminal and the contact ring. This red fiber insulation is known to be an early form in the T-H based lamps with procelain insulation becoming common in the 1890's.
It would be difficult for me to place a value on this lamp ther than to say it definately has value. In my opinion, pricing can be very subjective based on watching eBay auctions for several years.
Your bulb appears to be in good condition with an intact filament. Having the filament intact is essential to the value of the lamp, so if you want to test it, use an ohm meter to check for resistance rather than trying to light it up on house current. But from your picture it looks like it should work. The glass shows a little darkening. This is typical of carbon lamps that have been in service at one time. That could slightly effect value, but yours looks fairly clear, so not a big deal in my opinion. A lamp like this probably originally had a paper label on the envelope. Often, these don't survive (as in the case of your bulb), but when they do that can add to the value.
On a good day on eBay you could get a nice amount for this bulb. I've seen T-H based bulbs go for anywhere from $50 to $200 and up depending on the bulb and who's bidding.
Perhaps another collector looking at this sight might be more bold than I to give you an estimate. Good luck, and defrinately do not throw this bulb away!
Regards,
PCris
