Official Definition of Green

[TheEdge]

Just a query. Do the railways have an official definition of what green (and yellow and red) must be?

This stems from the fact that to my eye while the newer LED colour lights are clearly a very solid green older incandescent signals and semaphores sometimes look closer to a blue-green than actual green.

 

[DownSouth]

The blue-green colour of older signals using coloured lenses is probably a carryover of companies having supplied railways with the same lenses as they supplied for road traffic signals, where blue-green is used for the benefit of road users who have red-green colour blindness.

If people with any form of colour blindness (red-green is the most common) are precluded from being train drivers due to not being able to fulfil the duties safely, a pure green can be used for rail signals

LED clusters on road traffic lights here in Australia have a mixture of blue and green LEDs in the cluster to achieve the correct colour, while LED rail signals are purely green LEDs.

 

[t o m]

It's because the lenses on the old style signals are actually more blue than green. Incandescent lamps give off a yellowish light, not pure white like LED, so combined with the blue lens this makes a green.

A lens in a signal and a traffic light are both quite different. Traffic light lenses aren't designed to focus the beam in to the distance and they don't have a hot strip to focus the beam to the driver when close to the traffic light like a railway signal does.

 

[ac6000cw]

Yes there will be standards for colorimetry, beam shape, intensity etc. - there have to be to ensure consistency of performance between suppliers and across the network. Standards and specifications are the basis for any sort of quality control.

 

[TDK]

Just a query. Do the railways have an official definition of what green (and yellow and red) must be?

This stems from the fact that to my eye while the newer LED colour lights are clearly a very solid green older incandescent signals and semaphores sometimes look closer to a blue-green than actual green.

The official stance is Green, yellow and red. Some signals are slightly different in hue and are clearly more of a blue green than a true green but the terminology is green. Green is clear, 2 yellows is preliminary caution, single yellow is caution and red is at danger or stop.

 

[snowball]

The official stance is Green, yellow and red. Some signals are slightly different in hue and are clearly more of a blue green than a true green but the terminology is green. Green is clear, 2 yellows is preliminary caution, single yellow is caution and red is at danger or stop.

Yes but I think the original poster was asking about the standards that the equipment makers are required to work to, not the terminology used on the railway.

 

[John Webb]

The blue-green colour of older signals using coloured lenses is probably a carryover of companies having supplied railways with the same lenses as they supplied for road traffic signals, where blue-green is used for the benefit of road users who have red-green colour blindness.

If people with any form of colour blindness (red-green is the most common) are precluded from being train drivers due to not being able to fulfil the duties safely, a pure green can be used for rail signals

LED clusters on road traffic lights here in Australia have a mixture of blue and green LEDs in the cluster to achieve the correct colour, while LED rail signals are purely green LEDs.

May I gently point out that signalling companies were supplying railways long before road traffic signals were invented!
As explained by tom, the oil-lamps in signals gave a very yellow light, so the 'green' filter of a semaphore signal was, in fact, a blue one which combined with the yellow light gave green. When electric lamps were introduced into semaphores, the bulbs were deliberately under-run both to give a longer life and to retain the 'yellow' nature of the light, thereby avoiding the need to change the blue filter. In some of the remaining semaphore areas in the UK, LED lamps are replacing the filament bulbs, and either the LEDs are chosen to have a yellow tinge or the blue filter is changed for a green one.

 

[LexyBoy]

Good point on semaphores, I do recall that they have a blue "window" - makes sense now! (Don't think I've seen them lit, so hadn't occurred that it would give a green light).

In some of the remaining semaphore areas in the UK, LED lamps are replacing the filament bulbs, and either the LEDs are chosen to have a yellow tinge or the blue filter is changed for a green one.

Does anyone have an example (pic or location)? It seems rather inefficient to have a white LED lamp behind a coloured filter/lens, compared to replacing the unit with a dedicated LED signal.

It's because the lenses on the old style signals are actually more blue than green. Incandescent lamps give off a yellowish light, not pure white like LED, so combined with the blue lens this makes a green.

<pedant>LEDs emit a very narrow wavelength, so emit "pure" green, yellow, red or blue, but never white. This is great for signalling as it means you're not wasting energy filtering out the unnecessary wavelengths. White LEDs have a blue-emitting diode with a phosphor coating formulated to look white to the eye - actually the emission is more "spiky" than black-body radiation e.g. incandescent or sunlight, which is why some colours look strange under LED lighting.</pedant>

"White" LEDs often look very white or even blue; this is especially noticeable with cheap ones. Partly this is because the better phosphors are more expensive or patent protected, but also because the eye is more sensitive to green/blue light so you get more apparent brightness for the same power.

Another advantage of LEDs for signalling is that the emission is very directional, so lenses are not required.

 

[matchmaker]

The correct term for the "window" in a semaphore signal is spectacle!

 

[ac6000cw]

Just out of interest, does anyone know if the UK standards (which would have been formulated when incandescent lamps + filters were the norm) have been modified to allow for possibly slightly different 'native' Red/Yellow/Green colours from simple LED's - to avoid having to use a filter as well to get an exact match with the old standards ?

(I'm thinking about colour light signal heads here, not converted semaphore signals).

 

[W230]

Good point on semaphores, I do recall that they have a blue "window" - makes sense now! (Don't think I've seen them lit, so hadn't occurred that it would give a green light).

I'd had also noticed this but never put two and two together! I think the semaphores on the line between Norwich and Great Yarmouth have blue "spectacles".

 

[John Webb]

Just out of interest, does anyone know if the UK standards (which would have been formulated when incandescent lamps + filters were the norm) have been modified to allow for possibly slightly different 'native' Red/Yellow/Green colours from simple LED's - to avoid having to use a filter as well to get an exact match with the old standards ?

(I'm thinking about colour light signal heads here, not converted semaphore signals).

As far as I am aware, the standard has some degree of latitude built into it, but for consistency the LEDs for modern colour light signals are chosen so that their spectral output complies with the standard and therefore matches existing sources, whatever they may be. Filters are not used.

 

[Class172]

I'd had also noticed this but never put two and two together! I think the semaphores on the line between Norwich and Great Yarmouth have blue "spectacles".

All of the semaphore signals I have seen close up in my local area have blue spectacles - one signal just outside the station was recently replaced with a brand new semaphore (not colour aspect surprisingly), but it's hard to tell if that has a blue or green spectacle: I suspect the former since it's probably using the arm from the signal it replaced.

 

[Railsigns]

The correct term for the "window" in a semaphore signal is spectacle!

And the correct term for the "bulb" is lamp!

 

[ac6000cw]

one signal just outside the station was recently replaced with a brand new semaphore (not colour aspect surprisingly)

Yes, NR seem to be keener on doing that - maybe they feel that it's better to keep all the signals in a 'box area consistent (whereas BR seemed to do whatever was cheapest/easiest sometimes !)

So the important question - does it have a GWR finial on top of the post ?

 

[Class172]

So the important question - does it have a GWR finial on top of the post ?

It even has a GWR finial... http://roscalen.com/signals/DroitwichSpa/index.htm#NewUpStarter

 

[Cliveblackpool]

A reason of having a very blue green could it be that because blue has a longer wavelength than green, and would therefore travel further, especially in poor weather! Red has the longest wavelength. The old oil lights had a small flame - about half an inch high, and would burn for a week+ on a pint of oil, behind the focused bullseye lens.

 

[Railsigns]

A reason of having a very blue green could it be that because blue has a longer wavelength than green, and would therefore travel further, especially in poor weather! Red has the longest wavelength.

Blue has a short wavelength, shorter than green, yellow and red. Blue lights aren't good for long distance viewing.

 

[ac6000cw]

It even has a GWR finial... http://roscalen.com/signals/DroitwichSpa/index.htm#NewUpStarter

Yes, looks good (for a modern semaphore - pity about the access platform they have to have nowadays, for understandable reasons). A replacement semaphore I saw at Barnetby a few years ago looked awful - chunky square metal post for the lower 2/3 with a round post grafted on top for the upper 1/3 of the post - yuk!