Red is red is red. But it’s not.

The transformation of signalling with LEDs

Unipart Dorman LED signalling is now SUCH a part of the railway signalling system, that it’s easy to forget what a huge technical accomplishment the innovation was at the time – especially when you can get LEDs in all colours these days.

The development of LED signals was important to reduce the reliance on filament lamps (which were replaced every six months) – replacement that required maintenance crews to be trackside and in danger – and hugely costly.

The problem the industry faced was recreating the exact colours of the red, amber and green aspects in filament signalling – important in ensuring that drivers would recognise the signals for what they were. This had proved elusive for years for a variety of reasons:

  • The precise LED colours required were not available
  • LED light output declines over time, and the colour output changes too
  • With such low currents needed to drive the LEDs, lamp proving was difficult
  • The light ‘cone’ produced by signals meant that close-up the lit signal was difficult to see
  • ‘Phantoming’ (reflected light from an unlit signal) could confuse drivers.

To crack the barriers it needed a company from outside the rail industry – one with extensive experience in using LEDs in the road traffic business that could add value to the industry – and that was Dorman.

Dorman up to that point was a market leader in a range of products including vehicle beacons, vehicle activated signs, and the ubiquitous cone lights you see in roadworks – still a major part of the business. But their long history made them experts in the combination of light output and lens technology.

Clive Porter – lead Engineer on the LED signal innovation breakthrough, is still one of our key innovators and currently developing a range of signals for the North American market. He says of the development “It was a fiendish problem. Rightly, Railtrack were very cautious of replacing a ‘tried and tested’ signal with LEDs and it took us quite some time to get the combination of the right LED driven with clever electronics and lens technology to demonstrate to the Acceptance team that the new LED signals were compliant to the Standard and to grant us the PA certificate. We were elated when that was issued to us!”

Indeed, the electronics were important – not only because of the ability drive the LEDs in a way that ensured constant and consistent light output over time, but also to make the signals ‘visible’ to the interlocking and to ensure that Lamp Proving was also facilitated. The design was also key to ensuring that the new LED modules could be retrofitted into existing housings – together with unique ‘eyebrows’ of LEDs that meant the signal aspect was clear, even close up.

It was during the development of the signal that Dorman was acquired by (then) NRS and eventually became Unipart Dorman when NRS became Unipart Rail.

With huge numbers of Unipart Dorman signals now in service, the Innovation Team has continued to deliver innovative technology around the signal:

  • Integrated Lightweight Signal (iLS) – a new approach to signals using GRP signal heads and posts
  • Assisted Lift Trunnions to eliminate working at height
  • Self-cleaning lenses that effectively delivers zero maintenance for ten years.

It’s against this backdrop of incredible innovation over 20 years that it is clear that Unipart Dorman transformed the world of signalling.

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Values: Innovation, Performance, Risk, Cost, Safety