Thorn Beta 4

Lantern acquired in April 2009.

Thanks to Richard James of Harrison Lighting for this unused lantern.

The lantern features a polycarbonate prismatic refractor bowl - this is the more unusual variant; many Beta 4s had transparent bowls with little in the way of optical control incorporated into them.

The recess for the lantern locking screw can be seen when the lantern is viewed from above.

The individual refractor grooves can be seen when the lantern is viewed from this angle.

The lantern is not fitted with a lampholder - presumably these had to be ordered and fitted separately. All that is included is a small envelope containing a length of heat-resistant silicone sleeving for use when wiring up the lantern.

The lantern was fitted to an AC Ford AC184 wall bracket on Monday, 22nd June 2009. The short (150 mm) outreach of the bracket was necessary to avoid causing an obstruction in the loft room.

A draw wire had already been installed when the photograph was taken - this will act as a guide when the supply cable is fed in.

A 20 mm compression gland has been installed in the bracket's cable entry hole.

I decided to run the lantern as 80 W MBF using a 3-BC lampholder; curiously, the focusing mechanism only mentions Edison Screw lampholders for 80 W and 125 W MBF lamps. The focusing mechanism of older Beta 4s was slightly different, as the mercury options were only available with 3-BC lampholders.

The lantern/bracket combination was then installed, connected up and switched on - the moulded refractors proved very effective at dissipating the light output.

Lantern warm-up video:

Testing the fitting with my energy monitoring device revealed the following results:

Test Voltage (V) Current being drawn at full power (A) Calculated wattage (W) Apparent Power (VA) Frequency (Hz) Power Factor True Power (W)
240.2 0.4 89 96 49.9 0.92 88.39

Wardle Avon | CU Phosco P178




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