Thorn Beta 79

Lantern acquired in July 2017.

This lantern was an eBay purchase and appears to have been sold as unused old stock from an electrical wholesaler in Ireland. Whilst the 100 W version was always a relatively uncommon lantern, the 70 W version could be seen in greater numbers around Derby and Derbyshire, but never to the extent to sister lantern, the Beta 5, owing to the preference for SOX lighting. The 70 W Beta 79 was popular in Ireland, however, which is probably why this particular lantern was exported there, but luckily for me, proved surplus to requirements, and duly entered the Collection.

Having never been exposed to the outdoors, the lantern's GRP canopy remains shiny, smooth and, above all, clean! Despite the change to the canopy material from the original aluminium-canopied version, the overall appearance of the lantern changed little over the years that it was in production.


This particular lantern is not equipped with a NEMA photocell socket (or indeed, any type of photocell control), though because most lanterns would feature such a socket, its position is included within the canopy moulding. The four bolt heads seen here serve as part of the lantern's means of being attached to a bracket.


One noticeable alteration that Thorn made to the Beta 79 in the 1990s was the deeper bowl, complete with improved light distribution methods for the area situated below the lamp - a series of arcing refractor grooves surrounded by a diffuse effect to the polycarbonate. The lamp control gear is housed in the rear of the lantern, behind the black powder coated steel panel.


An expandable rubber grommet fits around the bracket entry, ensuring a good seal, regardless of whether the lantern is fitted to a 34 mm or 42 mm bracket diameter. Helpfully, the word 'Top' is moulded into the uppermost part of the grommet.


The refractors are moulded onto the inside of the bowl, along with the letters 'HP', which I have a feeling may represent the 'High Performance' optic.


Two side and one above-lamp reflector are fitted within the optic. All are made of the same 'bubbled' aluminium sheeting that is often used for direct reflectors in lanterns and floodlights.


The identification label is situated in the inside-front of the lantern. In the 100 W version, the lampholder is situated at this position instead. The lantern carries two IP ratings - 65 for the lamp area, and 44 for the gear area and wiring.


Speaking of the gear area, the components are all attached to the inside of the steel panel, which hinges downwards when access to the wiring is required. The bolts seen earlier pass through the canopy and work are used to clamp the lantern to its bracket.


The gear comprises a SHP 70 AE/AI ballast, a G53503 ignitor (both made by Thorn) and a 10 F capacitor, which looks to date to week 48 of 1996 (25th - 29th November).


The lantern was attached to a wall bracket on Friday, 18th May 2018.


Once switched on, the lamp warmed up to full brightness within a few minutes.


As with the 100 W version, the lantern's canopy is so thin that it becomes translucent with the lamp running.


Lamp switch-on 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
241.1 0.56 94 135 49.9 0.68 91.81 21.81 31.16%

Philips SGS 203 | Philips 'Streetfighter' SGS 101




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