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Patterns in LED Traffic Lights in Austin TX

Nearly all of the traffic lights in Austin TX are now using LEDs.
That said,

All the Green lights are arranged in a circle. There is clearly a
center LED, and all the other LEDs are arranged in circles around the
center.

All the Red lights are arranged in a honeycomb pattern. Thus along
the edges, you can see these little black notches where the honeycomb
pattern doesn't quite fit the circle.

All the Yellow lights are arranged differently. I can't remember
exactly how at the moment, because I so rarely close enough to the
light when it is yellow to examine the pattern.

The "burning" question is why? Why would all the LED lights in Austin
follow this rule? Does it have something to do with how many LEDs
they are trying to pack in to get an even brightness when green is
compared to red is compared to yellow? (One Guess) Or is it just a
design thing (another Guess). I have done some web searches, as have
some other engineers I know, and we have all come up empty.

Thanks!
 
Nearly all of the traffic lights in Austin TX are now using LEDs.
That said,

All the Green lights are arranged in a circle. There is clearly a
center LED, and all the other LEDs are arranged in circles around the
center.

All the Red lights are arranged in a honeycomb pattern. Thus along
the edges, you can see these little black notches where the honeycomb
pattern doesn't quite fit the circle.

Are they actually a "honeycomb pattern" which is a hexagon or are
they octagonal like a "stop" sign?

This could be for the benefit of those that are color blind so
that they could distinguish exactly what the light means like they
used to have the lights arranged in a particular pattern if they were
in the horizontal rather in the usual vertical.
 
Nearly all of the traffic lights in Austin TX are now using LEDs.
That said,

All the Green lights are arranged in a circle. There is clearly a
center LED, and all the other LEDs are arranged in circles around the
center.

All the Red lights are arranged in a honeycomb pattern. Thus along
the edges, you can see these little black notches where the honeycomb
pattern doesn't quite fit the circle.

All the Yellow lights are arranged differently. I can't remember
exactly how at the moment, because I so rarely close enough to the
light when it is yellow to examine the pattern.

The "burning" question is why? Why would all the LED lights in Austin
follow this rule? Does it have something to do with how many LEDs
they are trying to pack in to get an even brightness when green is
compared to red is compared to yellow? (One Guess) Or is it just a
design thing (another Guess). I have done some web searches, as have
some other engineers I know, and we have all come up empty.

Thanks!

LED voltages vary with efficiency. I don't recall if the voltage
varies with color. Anyway, they may change the number of LEDs in a
string depending on operating voltage.

I recall the high efficieny LEDS are higher voltage.
 
J

John

Jan 1, 1970
0
Nearly all of the traffic lights in Austin TX are now using LEDs.
That said,

All the Green lights are arranged in a circle. There is clearly a
center LED, and all the other LEDs are arranged in circles around the
center.

All the Red lights are arranged in a honeycomb pattern. Thus along
the edges, you can see these little black notches where the honeycomb
pattern doesn't quite fit the circle.

All the Yellow lights are arranged differently. I can't remember
exactly how at the moment, because I so rarely close enough to the
light when it is yellow to examine the pattern.

The "burning" question is why? Why would all the LED lights in Austin
follow this rule? Does it have something to do with how many LEDs
they are trying to pack in to get an even brightness when green is
compared to red is compared to yellow? (One Guess) Or is it just a
design thing (another Guess). I have done some web searches, as have
some other engineers I know, and we have all come up empty.

Thanks!

You made some good guesses!

There are specifications for traffic signals. You can buy the specifications
at http://www.ite.org/

Among other things, the intensity, color, and angular emission
characteristics are specified. It is a very competitive business, so it
behooves the manufacturer to use as few LEDs as possible while still meeting
the specifications. Different manufacturers arrange the LEDs differently. In
addition, different colors using different quantities of LEDs may give rise
to different arrangements.

Signals are submitted to the state's department of transportation for
examination and, once approved, the manufacturer is put on a list of
approved suppliers. When a city is interested in changing from incandescent
to LED, they get the approved manufacturer list from the state. This gives
them a starting point. I don't know if the cities are required to use the
approved ones, but wouldn't you? As a result, you will see a certain
uniformity from city to city within the state.

You didn't ask about the rest of this, but I'm on a roll.

It might interest you to know that another specification for LED traffic
signals is power factor. Yep! They have power factor correction built into
each one. Night time dimming is optional. Maximum power is specified. Power
savings over incandescent is significant. As I recall, incandescent was
about 100 to 150 watts while the LED signals were on the order of 30 watts.
Imagine how much money that saves the taxpayer in electricity.

As I recall, cities replaced incandescents about once a year. The LED
signals usually have a 5-year warranty (but may last longer). That is a big
savings in bucket-truck trips. Also, when an incandescent goes out, it's
out. LED signals may loose an LED in a string causing a group of LEDs to go
out, but the signal is still functional. The current that is no longer used
in the dead string may be diverted to the active strings maintaining pretty
much the same overall intensity. The higher current may shorten the life of
the remaining LEDs, but at least the signal will still function and can be
replaced when convenient.

That's a few of the things I remember from working in the industry about 7
years ago. I'm sure technological advances have dated some of my comments,
but, there you are.

Cheers,
John
 
D

Don Klipstein

Jan 1, 1970
0
It might interest you to know that another specification for LED traffic
signals is power factor. Yep! They have power factor correction built into
each one. Night time dimming is optional. Maximum power is specified. Power
savings over incandescent is significant. As I recall, incandescent was
about 100 to 150 watts while the LED signals were on the order of 30 watts.
Imagine how much money that saves the taxpayer in electricity.

They got the power consumption for red and green ones down to 11-15
watts, and around 15 watts or a little more for yellow, a good 3 years
ago, maybe more.

The really efficient red and green LEDs have 2-3 times the luminous
efficiency of superlonglife vibration resistant incandescents, and roughly
2/3 of the light from incandescents is blocked by the red and green
filters.
As I recall, cities replaced incandescents about once a year. The LED
signals usually have a 5-year warranty (but may last longer). That is a big
savings in bucket-truck trips. Also, when an incandescent goes out, it's
out. LED signals may loose an LED in a string causing a group of LEDs to go
out, but the signal is still functional. The current that is no longer used
in the dead string may be diverted to the active strings maintaining pretty
much the same overall intensity. The higher current may shorten the life of
the remaining LEDs, but at least the signal will still function and can be
replaced when convenient.

That's a few of the things I remember from working in the industry about 7
years ago. I'm sure technological advances have dated some of my comments,
but, there you are.

- Don Klipstein ([email protected])
 
Are they actually a "honeycomb pattern" which is a hexagon or are
they octagonal like a "stop" sign?

This could be for the benefit of those that are color blind so
that they could distinguish exactly what the light means like they
used to have the lights arranged in a particular pattern if they were
in the horizontal rather in the usual vertical.

There are descriptions of lights on the web where the shape provides
a clear indication of the meaning of the light (i.e. Octagonal for the
red).
It seems that various other countries have traffic lights like this.
However, the shape difference here in Austin is so slight that only
when
you are very close can you see the difference. So while my
engineering
friends and I discussed this as a theory, it was pretty easy to
reject.
It does make me curious what light frequencies they pick for the
lights,
since staying a way from true red and green is supposed to make
traffic lights friendly to the color blind. But that is another
question...

Paul
 
D

default

Jan 1, 1970
0
Nearly all of the traffic lights in Austin TX are now using LEDs.
That said,

All the Green lights are arranged in a circle. There is clearly a
center LED, and all the other LEDs are arranged in circles around the
center.

All the Red lights are arranged in a honeycomb pattern. Thus along
the edges, you can see these little black notches where the honeycomb
pattern doesn't quite fit the circle.

All the Yellow lights are arranged differently. I can't remember
exactly how at the moment, because I so rarely close enough to the
light when it is yellow to examine the pattern.

The "burning" question is why? Why would all the LED lights in Austin
follow this rule? Does it have something to do with how many LEDs
they are trying to pack in to get an even brightness when green is
compared to red is compared to yellow? (One Guess) Or is it just a
design thing (another Guess). I have done some web searches, as have
some other engineers I know, and we have all come up empty.

Thanks!

Good observation - I hadn't noticed it but it is the same here South
East
 
So here are pictures of the traffic lights.

http://www.flickr.com/photos/[email protected]/

Nearly all the traffic lights in Austin use the pattern you see for
the green for green, the yellow pattern for yellow, and the red
pattern for red.

I say "nearly". A few days ago I noticed at the north end of town a
red light which used the green pattern.

So perhaps Austin is using three different vendors? Or perhaps the
intensity of the LEDs varies, and the pattern is picked to accommodate
different numbers of LEDs (I Haven't actually counted the LEDs, but to
my eye, the Yellow has more LEDs than the Green, which has more than
the Red.
 
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