The Mullard LSD2 is a specialised flash tube for high speed photography. The flash duration is given as 1 μS and the discharge is 35 Joules. The flash should be fired once a minute at maximum by a 5,000 V pulse to the trigger electrode.
This Philips flash tube is unmarked but looks to be very close in design internally to the Mullard tube and is the same size.
The trigger is brought out to a side terminal.
The electrodes are precisely machined probably from nickel whereas the Mullard tube looks to have copper electrodes.
The conical cathode.
The wide glass tube envelope is 30 mm in diameter and, excluding the ES base, is 124 mm tall.