About 10 years ago we found a box of old bulbs in a storage unit. We don't have any information on them, but we did sell a couple on ebay. Someone mentioned that they may be switchboard lights, but I haven't seen any switchboard bulbs that look like these.
They have a number printed on the glass (I pulled out a few and saw 300 and 500 printed on them). At the base on the metal, there is a handwritten number (different numbers). Can anyone 'enlighten' me as to what these are and if they may have any current value? We'd be truly grateful.