Thorn Diffusalux

Acquired in November 2020.

This new, old-stock miniature version of the Diffusalux batten was designed to be used as a nightlight, especially in hospital wards and similar locations. A number of the full-length versions were installed in one of the classrooms at my secondary school, following refurbishment, though these ran electronic ballasts and traditional linear fluorescent lamps, whereas this fitting employs a two-pin five Watt lamp and electromagnetic ballast.

The fitting was still enclosed within its original Thorn box. Oddly, the label visible here states that it was supplied without a lamp, but one was included. Perhaps, a contractor had placed lamps in these in readiness for their installation, but in the end, this never occurred.

The fitting measures 225 mm (885 inches) in length, 185 mm (728 inches) at its widest, and 98 mm (386 inches) in depth. The prismatic diffuser is sandwiched between two white polycarbonate end caps.

Whilst the sides of the diffuser feature linear refractors, the underside features a dimpled design. The outline of the lamp is just about visible through this diffusion.

The top part of the fitting comprises a white powder-coated steel tray with a central cable entry hole.

The end caps feature the logo that Thorn adopted in the early 1990s.

The two end caps are spring-loaded. Releasing them allows the diffuser to be removed, and access to the lamp, and internal wiring, to be gained. A Vossloh-Schwabe 5 - 11 Watt ballast is the only gear component, owing to the lamp having an integral glow starter built into it. No Power Factor correction capacitor is supplied. As well as the five Watt lamp seen here, a seven Watt lamp could be used instead (anything above that would be too long). Alternatively, the fitting could be supplied with a small bayonet lampholder and a 15 Watt pygmy lamp.

This close-up of the internal label reveals that the fitting was produced in week 36 of 2003 (the first week in September).

This view demonstrates the shape of the diffuser - the top part fits flush with the underside of the steel panel, allowing a better seal to be made between the two than exists with other fluorescent battens, which suffer with dirt and insects becoming trapped inside the diffuser.

A lead was connected temporarily, as a means of testing the lamp's operation. It powered up without issue, with the warm-white colouring of the lamp producing a gentle glow.

The lamp's outline remained obvious with the diffuser reinstated.

The side refractors helped to distribute the beam in a downwards direction.

Operation video:

Testing with my energy monitoring device revealed the following results:

Test Voltage (V) Current being drawn at full power (A) Measured wattage (W) Apparent Power (VA) Frequency (Hz) Power Factor True Power (W) Difference to rated wattage Percentage Difference
243.6 0.18 11 44 49.9 0.26 11.40 6.40 128.01%

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