Red means stop

[Jerra]

but why does green mean go? Is it because they're opposite colours?

[factor-fiction]

You could just as well ask why Red means stop

[bookbinder]

It's probably a case of: red means danger; green means it's safe.

[jno]

good question - I think the answer is 'probably' but I haven't been able to find anything definite.

http://en.wikipedia.o...ision_and_colorimetry

Red has long been used as a warning colour, perhaps because unlike blue and green it doesn't appear over a large area in nature (at least I can't think of any examples) and therefore stands out.

[jno]

this piece says traffic lights may be derived from port and starboard lights for ships, but doesn't say where that came from

http://en.wikipedia.o...raffic_lights#History

[chakka35]

This reminds me of a hobbyhorse of mine:

Looking at an old piece of electric cable it reminded me how sensible the colour-coding used to be:

RED for Line ('Live') - Red is the colour for danger

BLACK for Neutral - What is more neutral than black?

GREEN for Earth - Green for safety

Then some fatheaded committee or other got together and changed it all to the present system, which is:

BROWN for Line ('Live') - the colour of earth!

BLUE for Neutral - the symbolic colour of electricity!

YELLOW/GREEN for Earth - Quite meaningless.

Whereas the old system was self-evident, the new system is positively misleading.

And please don't say it is a help to colour-blind people. Pretty obviously such people should not be working on a job where getting the colours wrong could be lethal.

[saxy_jag]

Interesting that, chakka. The 'new' way is the only way I've ever learned and I remember it because green/yellow is the 'different' one (i.e. earth) and blue is the nearest colour to the neutral colour green (I think the acid/alkali scale has green as neutral). Therefore brown has to be live.

Re traffic lights - red is hot fire (danger), green is cool grass (safe).

Interesting that the 'official' colour of a first aid kit/paramedic is green, and an industrial 'safe place' sign is yellow.

[jno]

red is prosperity in China and mourning in southern Africa, as I recall. It may seem obviously heat/fire to us but other cultures think it just as obviously means something else.

[Captin Kirk]

anything to do with them being colours which can still be distinguised between if you are colourblind?

[jno]

well, red/green is allegedly the most common form of colour blindness, and I've got it to the extent that I can't see dark red flowers on a dark red bush (our camellias for instance) but I've never had trouble distinguishing between the much brighter reds and greens of traffic lights, so I wouldn't have thought it would be a problem on wires if they were sufficiently different in tone.

[chakka35]

Captin Kirk and jno, please read again the last sentence in my post.