OT Slightly - LED street lighting to be installed in Canada - not long for here ?

The latest locale to join Toronto and Raleigh in the LED City
initiative is none other than the home of the Wolverines, which
recently announced plans to replace about 1,400 street lights with
light-emitting diodes. The city is claiming that it will be the
nation's first to "convert all downtown street lights to LED
technology," and it's hoping to save around $100,000 per year in doing
so. Not surprisingly, Research Triangle Park-based Cree will be
providing the components for Ann Arbor's transformation, and it sounds
like it'll take a couple of years before the $630,000 project is
actually completed. Hopefully, it won't take quite that long before
the Maize and Blue can topple Ohio State again.

Taken from http://www.engadget.com/2007/10/19/a...ced-with-leds/
where there are other links

Is this going to be good or bad for clear skies ?

wrote:
The latest locale to join Toronto and Raleigh in the LED City
initiative is none other than the home of the Wolverines, which
recently announced plans to replace about 1,400 street lights with
light-emitting diodes. The city is claiming that it will be the
nation's first to "convert all downtown street lights to LED
technology," and it's hoping to save around $100,000 per year in doing
so. Not surprisingly, Research Triangle Park-based Cree will be
providing the components for Ann Arbor's transformation, and it sounds
like it'll take a couple of years before the $630,000 project is
actually completed. Hopefully, it won't take quite that long before
the Maize and Blue can topple Ohio State again.

Taken from
http://www.engadget.com/2007/10/19/a...ced-with-leds/
where there are other links

Is this going to be good or bad for clear skies ?

Well, LED's only work with one polarity (all diodes work like a one way
valve, letting current flow one way but not the other) so on alternating
current they will flicker at the same frequency as the mains (50 Hz in the
UK i think) which means there are 25 periods of darkness per second.

Could this mean we could use mains current as the clock to phase CCD's so
they are only "on" when the LED street lights are off. If whole cities are
LED lit we could, by phasing our light capture periods with the LED nulls,
have a huge improvement in the results we couyld acheive in built up areas.

Les

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think?"...Valerie Emmanuel

Les Hemmings a.a #2251 SA

Wasn't it Les Hemmings who wrote:

Well, LED's only work with one polarity (all diodes work like a one way
valve, letting current flow one way but not the other) so on alternating
current they will flicker at the same frequency as the mains (50 Hz in the
UK i think) which means there are 25 periods of darkness per second.

I'd guess that they'll probably use flicker-free LED lights for street
lighting. Such things do exist. Some people (e.g. me) find the flicker
from LEDs extremely annoying. I find it painful to look at the new LED
traffic lights that have been installed around here, and would go
bananas if whole streets were lit that way.

By the way: 50Hz would mean 50 periods of darkness per second, not 25.

--
Mike Williams
Gentleman of Leisure

On or about 2007-10-19,
Mike Williams illuminated us with:
Wasn't it Les Hemmings who wrote:

Well, LED's only work with one polarity (all diodes work like a one way
valve, letting current flow one way but not the other) so on alternating
current they will flicker at the same frequency as the mains (50 Hz in the
UK i think) which means there are 25 periods of darkness per second.

I'd guess that they'll probably use flicker-free LED lights for street
lighting. Such things do exist. Some people (e.g. me) find the flicker
from LEDs extremely annoying. I find it painful to look at the new LED
traffic lights that have been installed around here, and would go
bananas if whole streets were lit that way.

By the way: 50Hz would mean 50 periods of darkness per second, not 25.

Errm, sorry to be a paid, but wouldn't it be 100? 2 zero crossings per
cycle, no?

--
Mark
Real email address | If variety is the spice of life,
is mark at | why do we use cinnamon?
ayliffe dot org |

Wasn't it Mark Ayliffe who wrote:
On or about 2007-10-19,
Mike Williams illuminated us with:
Wasn't it Les Hemmings who wrote:

Well, LED's only work with one polarity (all diodes work like a one way
valve, letting current flow one way but not the other) so on alternating
current they will flicker at the same frequency as the mains (50 Hz in the
UK i think) which means there are 25 periods of darkness per second.

I'd guess that they'll probably use flicker-free LED lights for street
lighting. Such things do exist. Some people (e.g. me) find the flicker
from LEDs extremely annoying. I find it painful to look at the new LED
traffic lights that have been installed around here, and would go
bananas if whole streets were lit that way.

By the way: 50Hz would mean 50 periods of darkness per second, not 25.

Errm, sorry to be a paid, but wouldn't it be 100? 2 zero crossings per
cycle, no?

No. All diodes work like a one-way valve, letting current flow one way
but not the other. So they're dark for the whole half cycle where the
current flows in the opposite direction.

I guess one way to make flicker free LED lights would be to use pairs of
LEDs arranged with opposite polarity, so that both half cycles are used.

I also guess that for street lights, they'd be using "white" LEDs. The
way most "white" LEDs work is that the LED itself actually emits blue
light, but it is coated with a phosphor that absorbs some of that blue
light and fluoresces with a broad spectrum yellow light. The blue and
yellow give the appearance of white light, with loss of colour fidelity
in the red and green. The fluorescence effect lags behind the light
emitted from the LED.

--
Mike Williams
Gentleman of Leisure

Mike Williams wrote:
Some people (e.g. me) find the flicker
from LEDs extremely annoying. I find it painful to look at the new LED
traffic lights that have been installed around here, and would go
bananas if whole streets were lit that way.


The new LED cats eyes on the M20 leave trails like tracer shells in my
mirrors at night. And if i move my eyes i can see the flicker too...

Let hope there are not too many 50Hz stimulated epileptics out there...

Les

--
Remove Frontal Lobes to reply direct.

"These people believe the souls of fried space aliens inhabit their
bodies and hold soup cans to get rid of them. I should care what they
think?"...Valerie Emmanuel

Les Hemmings a.a #2251 SA

On or about 2007-10-20,
Mike Williams illuminated us with:
Wasn't it Mark Ayliffe who wrote:
On or about 2007-10-19,
Mike Williams illuminated us with:
Wasn't it Les Hemmings who wrote:

Well, LED's only work with one polarity (all diodes work like a one way
valve, letting current flow one way but not the other) so on alternating
current they will flicker at the same frequency as the mains (50 Hz in the
UK i think) which means there are 25 periods of darkness per second.

I'd guess that they'll probably use flicker-free LED lights for street
lighting. Such things do exist. Some people (e.g. me) find the flicker
from LEDs extremely annoying. I find it painful to look at the new LED
traffic lights that have been installed around here, and would go
bananas if whole streets were lit that way.

By the way: 50Hz would mean 50 periods of darkness per second, not 25.

Errm, sorry to be a paid, but wouldn't it be 100? 2 zero crossings per
cycle, no?

No. All diodes work like a one-way valve, letting current flow one way
but not the other. So they're dark for the whole half cycle where the
current flows in the opposite direction.

Fair enough. My mistake. It's too many decades since I studied this
stuff obviously!

I guess one way to make flicker free LED lights would be to use pairs of
LEDs arranged with opposite polarity, so that both half cycles are used.

That or use a full wave rectifier. But your suggestion is more likely
I'd agree. Presumably unless you're spending more cash to supply them
with DC, you'd pretty much do that anyway for more than one LED?

I also guess that for street lights, they'd be using "white" LEDs. The
way most "white" LEDs work is that the LED itself actually emits blue
light, but it is coated with a phosphor that absorbs some of that blue
light and fluoresces with a broad spectrum yellow light. The blue and
yellow give the appearance of white light, with loss of colour fidelity
in the red and green. The fluorescence effect lags behind the light
emitted from the LED.

The Cateye one I use on my bike does look very white. More so than the
blue tinged headlights you see on some cars these days and definitely
not green or yellow as some of the early ones were. But I've not
inspected it carefully enough to see whether I can see any phospher.

--
Mark
Real email address | "Did you sleep well?"
is mark at | "No, I made a couple of mistakes."
ayliffe dot org |

In uk.sci.astronomy message , Fri, 19
Oct 2007 23:40:33, Les Hemmings
posted:
wrote:
The latest locale to join Toronto and Raleigh in the LED City
initiative is none other than the home of the Wolverines, which
recently announced plans to replace about 1,400 street lights with
light-emitting diodes.

...
Is this

going to be good or bad for clear skies ?

They will require new fittings, and it's likely that any modernisation
of fittings will give, for efficiency, better direction of the light.


Well, LED's only work with one polarity (all diodes work like a one way
valve, letting current flow one way but not the other) so on alternating
current they will flicker at the same frequency as the mains (50 Hz in the
UK i think) which means there are 25 periods of darkness per second.

If directly driven with AC, 50 darks per second. But, at the very
least, it seems sensible to use full-wave rectification, so 100 darks
per second.

Being forward diodes, LEDs need to be driven by a current source rather
than a voltage source; that would, at least, narrow the darks.

Normally, AIUI, adjacent houses in a street are driven from different
legs of a 3-phase supply (one can see this where supply is overhead); it
seems likely that street lights would be likewise.

The AC mains could be stepped down to a suitable voltage by a 50Hz
transformer; but to generate high current low voltage DC from mains it's
much better to use a switching regulator IIRC; that switches at high
frequency (probably above audio; but ask a dog) and uses less magnetic
material.

I've done some of that myself, in a non-lighting context.

But one really needs to hear from the actual designers of such fittings
to see what is deemed cost-effective nowadays.

Could this mean we could use mains current as the clock to phase CCD's so
they are only "on" when the LED street lights are off. If whole cities are
LED lit we could, by phasing our light capture periods with the LED nulls,
have a huge improvement in the results we couyld acheive in built up areas.

It seems unlikely that enough flicker at 50 or 100 Hz would be
acceptable to users of the light. At switching frequencies, I'd expect
individual lamp standards to run at similar but different frequencies.


--
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Wasn't it who wrote:
Thus spake Les Hemmings ) unto the assembled
multitudes:

The new LED cats eyes on the M20 leave trails like tracer shells in my
mirrors at night. And if i move my eyes i can see the flicker too...

Coo, is that what they are? How are they powered - is it just by the light
of oncoming vehicles? There are some similar such items on the eastbound
A27 for a stretch after you exit the Southwick tunnel.

http://www.aixtron.com/press/0211e.htm

"Power is generated via solar cells and a storage battery."

But if that's the case, it's odd that they flicker.

--
Mike Williams
Gentleman of Leisure

On Sun, 21 Oct 2007 13:14:04 +0100, Mike Williams
wrote:

Wasn't it who wrote:
Thus spake Les Hemmings ) unto the assembled
multitudes:

The new LED cats eyes on the M20 leave trails like tracer shells in my
mirrors at night. And if i move my eyes i can see the flicker too...

Coo, is that what they are? How are they powered - is it just by the light
of oncoming vehicles? There are some similar such items on the eastbound
A27 for a stretch after you exit the Southwick tunnel.

http://www.aixtron.com/press/0211e.htm

"Power is generated via solar cells and a storage battery."

But if that's the case, it's odd that they flicker.
Not really.
The most efficient way to drive LED's, is with a PWM drive. This is
what is done with all the LED car light, and given the 'storage
battery' voltage won't match the requirements of the LED's, this is
the way the cat's eyes wll be done.

Best Wishes