WRTL Stela Square

Lantern acquired in October 2010.

Indal-WRTL's 'Stela' range of LED lanterns is perhaps the most well-known out of all the current LED offerings on the market, thanks to the large amount of media coverage it has received; most notably on the BBC's 'Look North' programme, when a road in Middlesbrough was relit with these lanterns - the report is available on YouTube. Derbyshire's first Stelas appeared in the village of Hayfield in June 2010 - coincidentally, these were also of the 18 LED 'Square' variety, although there are many alternative options.

The Stela's striking design makes it a lantern that is instantly recognisable whenever it is seen. The Square version of the lantern can only be mounted post-top to a column.

When installed, the centre section of the lantern is positioned horizontally, and the flat panel surround is angled. The rear section of the lantern is not as steeply banked as the rear section is - this prevents rain from building up in the recess on the panel. If a NEMA photocell were fitted, it would be installed in the curved section immediately above the column spigot entry.

The assembly is held together with nine grub screws - the three additional grub screws in the centre section hold the cover to the wiring in place. The lantern bears a little resemblance to the Atlas/Thorn Alpha 10, in terms of its shape. The square section measures 400 mm 400 mm.

Following the merger of Industria and Indalux Lighting, WRTL's parent company is now known as Indal - this company's logo is cast into the centre cover.

The 18 LED chips are arranged in a grid on the underside of the lantern. The Square is also available in 10 and 14 LED options. The shape of the lantern acts as a heat sink for the temperature-sensitive LEDs. Two further grub screws secure the lantern to the column.

The LED lenses are shaped so as to maximise the effectiveness of each LED chip.

With the centre cover removed, the very simple wiring of the lantern is revealed. The white box is the LED driver. Note that if a miniature photocell were fitted to this lantern, it would be positioned within the gear area, rather than outside as a NEMA socket would be.

Just visible on the right of this picture is a wiring guide for both photocell-controlled lanterns, and also for lanterns that do not incorporate a local automatic switching point.

Owing to rapid advances in LED technology, the power rating for the Stela lanterns has reduced by a few Watts since this particular lantern was produced, meaning that the stated 26 W consumption of this lantern will be different to that of newer versions.

Well, this lantern's gallery now seems to have changed into a game of Space Invaders, for some reason...

Of course not - this is just what happens when the lantern is powered up!

The LEDs are of a cooler colour temperature than those of the Mini Iridium are - probably around 4000K. Whilst warmer colour temperatures can make areas feel more inviting and not so clinical, the efficacy of the LEDs is greater at the blue end of the spectrum, and better column spacings can therefore usually be achieved with higher colour temperatures. Striking a balance between high efficacy and good colour appearance is key when designing LED-based schemes (the same is true for all lamps that incorporate a phosphor coating on a blue light source to improve its colour rendering ability).

Lantern operation video:

Testing the lantern 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 (W) Percentage Difference
239.6 0.09 20 22 49.9 0.94 20.27 -5.73 -22%

Thorn Beta 5 | GEC Z9532




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