Termed a special purpose lamp the 300 watt bulb is usually found in industrial settings such as on ships or in large factories. They are becoming harder to source but are still available at the moment.
It is just a very large GLS bulb so is dimmable and has a life of approximately 1000 hours. Needless to say it is not energy efficient at all!
GES E40 Base
100 mm diameter
213 mm tall