This exhibit has few indications as to type. It belonged to Jonathan's father who worked for GEC in the 1950s. Looking at the images shows just two contacts - on the Ediswan screw base. Within the envelope is a second sealed tube complete with pinch stems and seals. A pair of spring wire collars keeps the inner envelope centred. Attached to the leads are horizontal coils with both ends joined together.
One coil has droplets clinging to it - mercury. Thus it can only be a lamp, the double envelope construction indicates a high pressure mercury lamp that will require a ballast to limit the current.
Near the base is what looks to be a resistance.
The base end showing the coil and mercury droplets. The centre electrode is connected to the resistance and then to the other input connection. The central rod does not touch the coil. It looks close enough for the residual gas to ionise with the applied voltage and the discharge to then heat the coil producing the main working gas.
The GES base cap.
The lettering on the base reads 220 - 240 V and below 250W.
The top electrode is also in the form of a coil with both ends joined externally.
Thanks to Jonathan Glover for sending the images.
The wide glass tube envelope is 50 mm in diameter and, excluding the GES base, is 300 mm tall.
