Reminds me of the early quartz upgrades for scoop lamps! If it is for an architectural fixture, it very well may not have a letter code. Might just be a number designator (watts, bulb style, size of tube in 1/8ths of an inch.) I would expect you would have better luck looking in a standard lamp catalog then in a theater lamp catalog.
@JD I'd right. I've seen and spec'd it several times, but not for 15-20 years. As I recall, up to 250w, T10 or T12, all of which would be right for the wall wash fixtures shown.
Double globe might have certain thermal advantages for the application and you would be able to touch the globe of the lamp. Slightly higher output than a standard incandescent lamp of the same lamp life, slightly less output than a halogenstage and studio lamp of similar lamp life.