Thorn Gamma Basique

Lantern acquired in December 2010.

The original location of this lantern is unknown, although it was removed as part of Derby's Street Lighting PFI. Prior to the commencement of the PFI, the SOX Gamma Basique was often used as a replacement post-top lantern in Derby, after Thorn discontinued production of the long-serving Gamma 6 lantern in 2002/3.

A unique feature of the SOX Gamma Basique (compared with versions designed to run other lamp types) is the elongated canopy; a necessity due to the length of a 35 W SOX lamp. In a Gamma 6, the lamp extends into the base section. This is not possible in the Basique, owing to how the gear components are arranged. Despite this, the bowl fitted is dimensionally identical to that of the Gamma 6, allowing old lanterns to be fitted with new bowls, should the need arise.

This canopy is secured with two plastic bungs that are supposed to be tightened using a coin or similar product. These are extremely fiddly to locate on to the lantern's internal support rods, although this method does increase the rigidity of the lantern.

Unsurprisingly, the support rods extend well past the top of the bowl. The connections to the NEMA socket can be disconnected using the connector plug that is located to the right of the lampholder - this allows the canopy to be removed for lantern maintenance.

The lantern incorporates the same style of lamp support that featured in the Gamma 6.

The identification label would be located directly beneath the lamp when the lantern was in service. The panel that the label is applied to hinges upwards, in order to allow access to the capacitor and ignitor, as well as the lantern's main connector block, as shown below:

The lantern was manufactured in 2004, so it could only have seen six years of service as an absolute maximum. Despite this, the inside of the base casting is heavily corroded; as is the ballast. Somehow, I don't think that the lantern was sealed to anything like its stated IP65 during its time on the road!

The lantern was fitted to a post-top stand in October 2018, and, after a lamp was fitted, was powered up.


Lamp warm-up 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 0.52 57 125 49.8 0.49 61.43 26.43 75.52%

GEC Z9532 | GEC 'Dioptrion' Z8431




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