Interesting debate

230v nominal well that is for the maths part.  Now speak to someone in Yorkshire and they will tell you they get 247 to 250v on a regular basis.

As for the Manufacturer who make Traffic signals using incandescent lamps they need to speak to their R&D and get working on the LED version.  The cost savings for whoever pays for the street sign / Traffic signals pence/kWh should be a convincing factor.  100w lamp vs 15w LED Lamp.

I think they started to swap out the lights in London around 2014 from incandescent to LED lamps

Sergio Fernandez said:

As for the Manufacturer who make Traffic signals using incandescent lamps they need to speak to their R&D and get working on the LED version.  The cost savings for whoever pays for the street sign / Traffic signals pence/kWh should be a convincing factor.  100w lamp vs 15w LED Lamp.

The failure mode for most LED lamps is often to a stroboscopic output as opposed to off.

I’m sure there are LED traffic signals – I presume they’d need a bespoke driver so can’t be easily retrofit. I’ve got a client who manufactures railway signals with LED’s, and a former one who manufactures LED runway lamps. Both are subject to very stringent requirements so that they fail to a known safe state.

Incandescent lamps are a lot easier on this front – their failure modes are more obvious. If the controller detects an open circuit then it knows there’s a fault and can degrade into the safest state which in most cases is to trip all signals such that motorists will interpret as caution and give way. 

To me it seem quite obvious that LED used for outdoor like the following

Traffic signals

Runway lamps

Railway signals

should fail to safe. If they don't then there is common sense lacking and the design team need to be re-educated as to what the failing are.  As you say Strobe, which is annoying enough on a garden PIR floodlight but it is absolutely dangerous for a traffic signal or a run way at night in the rain (just adding risk to emphasise the point for future readers) I would then also go 1 step further


Get that unit to report back to central office for traffic signals or rail signal or control panel at an airport of its failure.  Designers need to make kit that is fit for purpose and fit for peer review.
UK traffic lights could be fitted with IoT technology quite easily.

The airport would also get further enhancements like secondary/redundancy light sets.   

It's all very well that a person knows the difference between these states.

But you've got do design a machine that knows, and meets a SIL rating. What happens if the visible front of a lamp appears off, but the monitoring equipment which can only see current and voltage doesn't see this? That's not too difficult if you're on a clean sheet design, but if you've got an existing mature design then it's not something you can just change.

Safety engineering is very hard work unfortunatly.

The Designers will need to work on it longer until

it is fit for purpose and fit for peer review.

Too many products come to Market before they are ready for the Market.  eg AFDDs

Which is why where things really matter, we often have the equivalent of incandescent lamps longer than you might like, such as a telephone standard with voltages and current levels based on carbon granule microphones and moving iron earpieces, with complex electronics at both ends emulating the original kit. Or, if it is a railway telephone, sometimes the actual original kit.

Mike

One advantage of incandescent bulb traffic lights is that they are much better at melting any snow which has accumulated on or around the lens.

I do feel like I've entered a bit of a time warp here, basically don't panic - all these issues were very thoroughly worked through around 20 years ago...probably longer in the highways world.

And yes, where applicable railway LED signals (or more accurately their control and monitoring functions) are SIL4.

I do remember one of my my colleagues in the early 2000s saying that LEDs could never work in rail signalling but he was a) a mechanical engineer and b) rather thoroughly proved wrong.

Cheers,

Andy

(formally UK Engineering Manager / Product Manager for (amongst other things) incandescent rail signals for a major manufacturer...delighted that that part of the role is now obsolete) 

wallywombat said:

One advantage of incandescent bulb traffic lights is that they are much better at melting any snow which has accumulated on or around the lens.

P.S. On this point, the person I mention above did also, quite correctly, regularly point out that the problem is that road traffic lights are the wrong way up! The problem doesn't arise with rail signals (at least as far as snow blocking the red signal which is the important bit).

Funny how when a subject comes up it immediately pops up again...I was helping a colleague with their CEng application this morning, and one of their bits of evidence is that they led a team who developed from scratch a rail signalling interlocking system in Turkey. We were looking for an example of consideration of sustainability, and they pointed out that they had introduced a new feedback and monitoring and control system in their interlocking logic to allow the use of low energy LED signals, including the safe detection of failures. I did smile at the coincidence that I'd only just written about that, not having thought about it at all for several years...

Funny how when a subject comes up it immediately pops up again...I was helping a colleague with their CEng application this morning, and one of their bits of evidence is that they led a team who developed from scratch a rail signalling interlocking system in Turkey. We were looking for an example of consideration of sustainability, and they pointed out that they had introduced a new feedback and monitoring and control system in their interlocking logic to allow the use of low energy LED signals, including the safe detection of failures. I did smile at the coincidence that I'd only just written about that, not having thought about it at all for several years...