Thorn Isaro Pro S

Lantern acquired in June 2019.

This lantern was removed from Column 18176 on Saint Helen's Street in Chesterfield, following a vehicular collision in October 2018 that saw the column damaged severely enough for it to require complete replacement. Although this lantern was intended to be fitted to the replacement column when this was installed, a new lantern was fitted instead, and so this lantern was kept in storage for use elsewhere. By 2019, the Isaro Pro S was a familiar lantern in some parts of Derbyshire; indeed, 8 W variants of this lantern were introduced on my own road in late April / early May, in place of the Philips MI 26 35 W SOX lanterns that had lit the road previously.

This July 2018 image, taken from Google Street View, shows the lantern when (freshly) installed. A Philips XGS 104 55 W SOX lantern mounted post-top to the previous column was situated here before the LED replacement work commenced.


The lantern comprises a die-cast aluminium construction, which, according to official Thorn literature, is of a highly corrosion-resistant grade. The lantern measures (L) 571 mm (1.7 ft), (W) 224 mm (8.82 inches) and (D) 114 mm (4.49 inches).


The NEMA socket is offset on the canopy, owing to the positions of internal connections. The Zodion ZCell photocell seen here is not the lantern's original photocell, but is identical to what would have been fitted when the lantern was in use. A stainless steel clip at the rear of the lantern secures the upper and lower sections of the lantern in normal circumstances.


Removing the cell reveals the date wheel for the NEMA socket, which indicates that it was manufactured in September 2017.


The Thorn logo is embossed into the underside of the lantern. The label visible alongside this provides the following details:

T = Thorn

26 = Wattage

P4 = Intended Lighting Class

Had this code been suffixed with an 'N', it would signify that the lantern was configured to run at full output throughout the night. As this is missing, however, the lantern is configured to dim automatically during quieter periods of the night, with its output reducing to 50% between midnight and 5 am.


The twelve LEDs are positioned behind a flat glass cover, which appears to have been splashed with a substance; possibly, this occurred in the aftermath of clearing up the damaged column. The optic is designed to accommodate multiple circuit boards, depending on the levels of brightness required; hence, the considerable amount of unused space surrounding the single circuit board in this lantern, and the looped connector wire, which would link to another circuit board, where fitted.


A pre-wired length of Arctic flexible cable was included with the lantern. Although this particular example is designed for post-top mounting on a 76 mm diameter shaft, the spigot is a separate piece, and could be swapped for a narrower side-entry spigot if required by removing the two bolts that attach it to the lantern. The bolts also serve as the means of setting the lantern 'tilt'. When installed post-top, the tilt is adjustable from zero to +20 degrees, and from -15 to +15 degrees when installed side-entry (lateral).


This back view demonstrates the very compact nature of the lantern.


Unfastening the clip causes the upper part of the canopy to hinge away from the lower part, breaking all electrical connections in the process. A cable bridge clamp should be fitted to the connector block, but is missing. A small sponge to the left of the cable entry hole allows a degree of breathability for the lantern interior whilst maintaining a high IP rating.


The lantern's identification label carries the date code 13 18, suggesting that the lantern was produced in Week 13 of 2018, which would be the 26th March - 1st April. Note that there is nothing on the part code that makes reference to the lantern's name; this is because it has to be known as a Civiteq 2 (no such lantern exists in reality) for procurement reasons at the Council.


The internal wiring is very straightforward, with the OSRAM 'Optotronic' driver having two input wires and two output wires. Oh, for the days of a veritable spaghetti of wires feeding a ballast, ignitor and capacitor in a street lighting lantern!


The lantern was fitted to a dedicated post-top wall bracket and the wiring threaded through the metalwork.


Powering it up was too much for my camera to handle; it turned the single strip of twelve LEDs into one full optic!


Zooming on the LEDs enabled the auto-exposure to allow them to be seen, however.


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
252.5 0.1 23 25 49.8 0.86 21.72 -4.29 -16.48%

Thanks to the dimmable LED driver incorporating DALI (Digital Addressable Lighting Interface) connections, the lantern can be dimmed manually using a special dimmer switch that is compatible with the DALI system. I decided to exploit this option and so re-wired the lantern using a five-core flex between it and the dimmer; the extra two cores providing the control from the dimmer. This photograph shows the lantern in its dimmest state.


Although not immensely different, owing to automatic exposure compensation, the image below details the lantern at full output.


Testing the lantern in these two different states revealed some interesting details. This shows the ratings with the lantern fully dimmed:

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
244.0 0.04 6 10 49.8 0.57 5.56 -20.44 -78.60%

Conversely, running the lantern at full power revealed these 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
244.0 0.1 24 24 49.9 0.93 22.69 -3.31 -12.72%

This video demonstrates the dimming operation more clearly.

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