My old (1980 + 1984) GE & Sylvania catalogs both list a 100w 120v A-19 inside frost incandescent lamp with a Left-Hand Thread Medium (E-26)  base    What would this have been used for and has anyone ever seen one . GE is code 100A/LHT and Sylvania is code 100A/4.  Sylvania also listed this base as available in 25- 150 watt .

ANY IDEAS

I think it was to keep people from stealing the bulbs, here’s some for sale   https://www.ebay.com/itm/VTG-lot-of-3-Marbled-Bakelite-Left-Thread-Light-Sockets-Factory-Industial-Lamp-/124130844586

Makes sense !

I have heard that these are sometimes used in hotels to keep people from stealing the bulbs, which apparently is an issue.

LH thread lamps were apparently used in situations where people might steal the bulbs, such as trains, etc. I'd love to get some, I've seen them but where do you get the lampholders..?

I think they also used left handed bulbs for temporary lighting in some situations. I’ve found the catalog number for one type of left hand socket: Leviton calls their’s 157-x, and it looks like a temporary lighting socket.

They also have them on amazon