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I imagine this one is identical to the UK where the flashing yellow allows you to proceed if/when the crossing is clear of pedestrians.

BTW when visiting Oz a few years ago, it took me some time to work out what a “PED XING” was on your American style (worded) road signs. It finally twigged when I nearly ran over one! Just joking!


[This message has been edited by Hutch (edited 04-21-2006).]

I've never really seen the point of the red-&-amber phase here. All it seems to do is encourage certain drivers to start off before green. It's also interesting to note that where we have a separate green "filter" arrow for turns, that can just come on with the red without any amber first.

Our neighbors across the water in Ireland have lights which just go straight from red to green, as do those in the Channel Islands.

By the way, we do not have any amber or red arrows, and for North American readers, neither do we have turns on red (except where there's the aforementioned green arrow illuminated simultaneously).


As Hutch said, that's standard for our pedestrian crossing lights. It's not used where there are also pedestrian lights at an intersection with regular lights. It's only on the lights which are normally located in the middle of the block with the sole purpose of stopping traffic for pedestrians to cross.

Whereas American lights flash the "Don't walk" or "red hand" immediately before going back to the solid "Don't walk" indication, ours flash the "green man" (walk) signal, and the amber for cars flashes at the same time.

http://www.highwaycode.gov.uk/signs01.htm

http://www.highwaycode.gov.uk/18.htm#172

They've started introducing different types of pedestrian crossing lights recently though, some of which now use the regular red/amber before green. Why we need a half dozen different types with varying light placement and different sequences, I have no idea.




One thing I have noticed about some French lights is that there's actually very little difference between the colors. In the U.K., the U.S., etc. red and amber are clearly and distinctly red and amber.

Some of the lights in France seem to use a reddish-orange for one and a not-so-reddish-orange for the other, and at first glance you can't actually tell which is which (without looking at the position on the signal head).


I've had to explain this American sign to a few fellow Brits before:




[This message has been edited by pauluk (edited 04-22-2006).]

The irony is that the orange lights are ON for the shortest time, you expect them to last the longest.
The red ones do most ON hours but I haven't seen those faulty yet.

How is the life span of LEDs calculated? are the like incandecants where they have xyz hours life. Or are they like flourecents where you shorten there life the more they are switched off and on?

Kenbo, Welcome to ECN.

Leds: Their lifespan is based upon 'running' hours at their nominal operating voltage and current. ( around 100,000 hrs )
In case of Red Led's 1.7 volts dc 20 mA
Yellow and Green Led's 2.2 volts dc 20 mA
Blue and White Led's 3.6 volts dc 20 mA
to give some examples. ( Data sheets are usually available from the LED suppliers.
and quoted values above may vary a little )

An LED is a light emitting diode. In forward biased mode at the U.nom and I.nom, the LED emits light. Is an LED subjected to a higher current The LED will overheat and fail eventually or loose a lot of it's brightness before failing altogether.
An LED does not like to be reversed biased and a reverse voltage of about 5 to 6 volts dc can be fatal for the LED.
An LED can be pulse driven at a lot higher current provided the ON OFF ratio is adequate for a cool down period of the LED.
e.g. 100mA for 50mSec and OFF for 500 mSec.

Under normal running conditions LED's don't get warm at all.

The newer Luxeon LED's like the 1, 3 and 5 Watt types are a whole different cattle of fish. These are supplied with data sheets and have to be adhered too otherwise they will fail earlier than expected and they are expensive to destroy by means of a wrongly applied voltage and the like.

An LED is not affected by the amount it's switched ON or OFF.
Effectively at 50 or 60 Hz ac the Led will pulse at the frequency. It's important that an antiparrallel diode is fitted across the LED to protect it from reversed applied voltage.

In traffic lights LED's are usually fitted in strings of 5 or 6 in series with a suitable dropper resistor to avoid loosing all the LED's in case one LED failed.

Led on photo is Red LED on 230 Volts 50 Hz
2 x 33k resistor and 1N4007 diode in series.
1N914 or eq. in antiparrallel.
yields about 3 mA through LED for a long lifespan.



edited for typo's and photo insert. Raymond

[This message has been edited by RODALCO (edited 04-26-2006).]

[This message has been edited by RODALCO (edited 04-26-2006).]

[This message has been edited by RODALCO (edited 04-27-2006).]