Traffic lights (national standard for wavelengths?)

[Dustin DeWinn]

I didnt see anything about this in the MUTCD, but is there a standard for the wavelengths traffic lights are emitted at?

In other words is it the same red, amber, and green everywhere, or is there variation allowed as long as they are within the red, yellow, green nm range?

I know there are different generations of traffic lights, so this wouldn't be uniform, but I'm talking latest generation ones....are they all projected at the same wavelength so they're the same green, etc everywhere?

I see no such rule or standard and theres a range for what counts as red, green, etc?

[02 Park Ave]

🚦There has to a standard.  All red lights have to be on the same wavelength.  How else would our autonomous vehicles "recognise" them?🚦 

[Scott5114]

As far as I know, the only standards are that they are "red", "green", and "yellow". There is no specification of what constitutes each of those colors.

As for what actually gets produced, it varies by manufacturer. As long as it looks green, the manufacturer is in the clear. So in some areas you might more bluish or yellowish greens.

[kalvado]

First, it is not wavelength - it is color range on chromaticity diagram.
Here are the ranges as defined by FHWA: https://www.fhwa.dot.gov/publications/research/safety/13018/001.cfm

[kalvado]

First, it is not wavelength - it is color range on chromaticity diagram.
Here are the ranges as defined by FHWA: https://www.fhwa.dot.gov/publications/research/safety/13018/001.cfm

Looks like things are bit different for traffic lights
I cannot find root source, but this is what is mentioned elsewhere - basically red and yellow have to be more saturated:

[kalvado]

And whatever it worth:

SAE - society of automotive engineers, ITE - Institute of Transportation Engineers
This image comes from the website of a company making colored lenses...

[paulthemapguy]

What in the hell is chromaticity
and how does it relate to wavelengths?
What do the axes on the graphs mean?  Does anyone know?  I was about to say, my favorite graphs are the ones where the axes aren't even labeled.

[kalvado]

What in the hell is chromaticity
and how does it relate to wavelengths?
What do the axes on the graphs mean?  Does anyone know?  I was about to say, my favorite graphs are the ones where the axes aren't even labeled.

it is 2017.. Typical directions are  take Google, then Wikipedia exit..
park at https://en.wikipedia.org/wiki/Chromaticity

[jeffandnicole]

Or, even better, go straight to the state's DOT website, which may contain the actual guidelines they use.

This is NJ's Electrical Material Specifications Index page:  http://www.state.nj.us/transportation/eng/elec/TSS/english/  Clicking on any of the topics produces what they permit for each subject.  If it's not specifically mentioned, then there's probably a guideline that is followed. 

For example: By clicking on the Green LED Traffic Signal Module Spec, it reads at Section 2-6:

The beam color, beam intensity, and radiation pattern shall conform to the requirements for maintained minimum luminous intensity for LED signal modules and chromaticity as specified in the ITE (VTCSH, PART 2) standards.

[TheArkansasRoadgeek]

As far as I know, the only standards are that they are "red", "green", and "yellow". There is no specification of what constitutes each of those colors.

As for what actually gets produced, it varies by manufacturer. As long as it looks green, the manufacturer is in the clear. So in some areas you might more bluish or yellowish greens.

I was watching a YouTube video,

and in the video the light uses what seems to be a blue bulb with a green lense.

*Not to say that this is the case with every design of the light! Clearly this light is a luminescent type. But, this is interesting how they pulled this off!

[Pink Jazz]

I know for incandescent signals, to aid those in red-green color blindness, the red signal was required to have a slight orange hue, and the green signal was required to have a slight blue hue.  However, I wonder if this has been changed for LED signals.

I have noticed though that frequently with LED signals though that green signals generally have clear lenses, although green-tinted lenses are now making a comeback with incandescent-look LED signals.

[jeffandnicole]

As far as I know, the only standards are that they are "red", "green", and "yellow". There is no specification of what constitutes each of those colors.

As for what actually gets produced, it varies by manufacturer. As long as it looks green, the manufacturer is in the clear. So in some areas you might more bluish or yellowish greens.

I was watching a YouTube video,

and in the video the light uses what seems to be a blue bulb with a green lense.

*Not to say that this is the case with every design of the light! Clearly this light is a luminescent type. But, this is interesting how they pulled this off!

If you look at the 8:04 mark, it's a clear bulb for the green light. 

[TheArkansasRoadgeek]

As far as I know, the only standards are that they are "red", "green", and "yellow". There is no specification of what constitutes each of those colors.

As for what actually gets produced, it varies by manufacturer. As long as it looks green, the manufacturer is in the clear. So in some areas you might more bluish or yellowish greens.

I was watching a YouTube video,

and in the video the light uses what seems to be a blue bulb with a green lense.

*Not to say that this is the case with every design of the light! Clearly this light is a luminescent type. But, this is interesting how they pulled this off!

If you look at the 8:04 mark, it's a clear bulb for the green light.

Ok, it was their cluelessness that made me look a little dumb. But, the video was cool.

[roadfro]

Ok, it was their cluelessness that made me look a little dumb. But, the video was cool.

It was cool, except for the whole "destroy the traffic signal head" part of it... I'd want to wire it up to a control box to play with it (my high school calculus teacher actually had a signal head wired up in this way, in our classroom).