Why do street lights flicker in snowy weather?

[Eddie]

In the UK we currently have cold winds and snow.

A radio phone-in got a lot of people talking about flickering street
lights.

Is there a real connection between bad weather and flickering street
lights. If so then how does it work?

 

[Adrian C]

Can you be precise? Frequency of flickering? Snow required? humidity?
Cold? Exceptions?

Tea.

 

[Archimedes' Lever]

Can you be precise? Frequency of flickering? Snow required? humidity?
Cold? Exceptions?

Light reflecting off the snow causes the opto-sense switch to trip?

I have seen light flicker in good weather, so your claim of cause and
effect are likely flawed.

IOW, it isn't the weather or the temperature. It is observer error.

 

[Eddie]

Can you be precise? Frequency of flickering? Snow required?
humidity? Cold? Exceptions?

The flicker I saw a few days ago was about 2 or 3 times a second.

The radio callers weren't specific about their local conditions but
just said "my street light is flickering here too".

In my case in South East England a cold snap was just starting and
there was about 2 inches of snow and temperatures were a few degrees
below freezing. The winds were unusally high for the area (perhaps
VERY roughly 30 mph).

It could just be coincidence but the radio callers got me thinking
that maybe there's an electrical explanation. Any observations or
ideas?

 

[johnwright]

The flicker I saw a few days ago was about 2 or 3 times a second.

The radio callers weren't specific about their local conditions but
just said "my street light is flickering here too".

In my case in South East England a cold snap was just starting and
there was about 2 inches of snow and temperatures were a few degrees
below freezing. The winds were unusally high for the area (perhaps
VERY roughly 30 mph).

It could just be coincidence but the radio callers got me thinking
that maybe there's an electrical explanation. Any observations or
ideas?

I wouldn't have thought there was anything electrical about it, unless
it was variation in the supply. Most street lights are low pressure
sodium lights and run internally at about 100C in order to vapourise the
sodium - all internally generated by the initial argon/neon discharge -
one reason they take several minutes to warm up as do most light
sources other than incandescent or LED light sources being notable
exceptions.

This in itself makes them insensitive to ambient conditions.

There would be a variation in warm up time depending on the ambient
temperature - the colder it is the longer it takes. (You can see this
with CFL lights especially ones used outside. The ones I have in my yard
take several minutes to produce full output especially when its really
cold outside). Even the HP sodium lights you often see take time to warm
up as well. They are like LP sodium lights except the two well known
sodium lines are pressure broadened to give better colour rendering.

 

[Steve Firth]

It could just be coincidence but the radio callers got me thinking
that maybe there's an electrical explanation. Any observations or
ideas?

Yes, it's quite simple. Callers to local radio stations are drawn from
the lower 5% of human ability. Anything they say can be safely ignored
because it's bound to be vacuous crap. HTH.

What local radio needs is another James Stannage to tell the dimwits
phoning in that they are indeed dimwits who are a waste of oxygen that
could be used more productively on keeping slugs alive.

 

[Mike Barnes]

What local radio needs is another James Stannage to tell the dimwits
phoning in that they are indeed dimwits who are a waste of oxygen that
could be used more productively on keeping slugs alive.

Sadly, I don't think there will never be another James Stannage. Thanks
for reminding me of him. You and he have a lot in common.

 

[Steve Firth]

Sadly, I don't think there will never be another James Stannage. Thanks
for reminding me of him. You and he have a lot in common.

Such kind words, and I do actually mean that. I had a deal of respect
for the bloke ever since I accidentaly tunesd into Piccadilly Radio when
I was a student. Listening to him baiting the drunks who phoned in late
on Friday night was a pleasure.

 

[Tzortzakakis Dimitrios]

In the UK we currently have cold winds and snow.

A radio phone-in got a lot of people talking about flickering street
lights.

Is there a real connection between bad weather and flickering street
lights. If so then how does it work?

Because of utility privatisation they don't service the lights, exchanging
blown bulbs with fresh ones?

 

[Mike P]

Yes, it's quite simple. Callers to local radio stations are drawn from
the lower 5% of human ability. Anything they say can be safely ignored
because it's bound to be vacuous crap. HTH.

What local radio needs is another James Stannage to tell the dimwits
phoning in that they are indeed dimwits who are a waste of oxygen that
could be used more productively on keeping slugs alive.

Heh. I remember him. Alan Beswick was another local radio hero...

Mike P

 

[jmfbahciv]

Steve Firth wrote:

<snip> that wasn't helpful at all.

/BAH

 

[jmfbahciv]

In the UK we currently have cold winds and snow.

A radio phone-in got a lot of people talking about flickering street
lights.

Is there a real connection between bad weather and flickering street
lights. If so then how does it work?

When I lived in Massachusetts, the only times my lights flickered was
during lightning storms. Most of that occurred when demand was almost
equal to capacity.

Can you describe the flickering? Were the lights really flickering
or was the snow so bad that snow blown sideways blotted out the light
momentarily?

/BAH

 

[Andrew Gabriel]

The flicker I saw a few days ago was about 2 or 3 times a second.

I've seen this with SOX (low pressure sodium) lamps as one of
the end-of-life failure modes, although it's not the most common
SOX failure mode. With the 35W SOX used on smaller roads, it could
be the starter repeatedly restarting a lamp which isn't sustaining
an arc anymore.

The radio callers weren't specific about their local conditions but
just said "my street light is flickering here too".

Description too devoid of information to even guess on the
cause. They could each be describing something completely
different.

In my case in South East England a cold snap was just starting and
there was about 2 inches of snow and temperatures were a few degrees
below freezing. The winds were unusally high for the area (perhaps
VERY roughly 30 mph).

If the streetlamps have their own didicated overhead
supply (now very rare in the UK), then maybe that's
arcing somewhere in the wind.

 

[James Sweet]

In the UK we currently have cold winds and snow.

A radio phone-in got a lot of people talking about flickering street
lights.

Is there a real connection between bad weather and flickering street
lights. If so then how does it work?

Cold temperature raises the strike voltage of discharge lamps. HID lamps
have small arc tubes which warm up quickly and are less prone to this,
but low pressure sodium lamps common in Europe (the saturated orange
ones that are pink when they first come on) have long discharge tubes
with a lot of surface area and are electrically more similar to
fluorescent lamps may have more trouble in cold weather. If the strike
voltage is higher than the peak voltage the ballast can deliver, the arc
will extinguish. If the voltage is just barely sufficient, the lamp can
flicker.

 

[TKM]

Cold temperature raises the strike voltage of discharge lamps. HID lamps
have small arc tubes which warm up quickly and are less prone to this, but
low pressure sodium lamps common in Europe (the saturated orange ones that
are pink when they first come on) have long discharge tubes with a lot of
surface area and are electrically more similar to fluorescent lamps may
have more trouble in cold weather. If the strike voltage is higher than
the peak voltage the ballast can deliver, the arc will extinguish. If the
voltage is just barely sufficient, the lamp can flicker.

This explanation confirms what I see with such lamps in cold weather. The
older the lamp, the higher the strike voltage and so the more likely it is
to flicker. Eventually, the energy from the flickering arc should warm the
lamp enough to sustain it without flickering (unless the lamp is at
end-of-life) so it would be interesting to hear from anyone who has watched
a flickering lamp for a while to see if that indeed does happen.

Someone mentioned that the cause of the flicker might be due to the
luminaire's photocell getting mixed signals due to reflection from the snow.
Photocells usually have a delay circuit built in; otherwise, they would
react to lightning flashes or headlight beams sweeping by.

TKM

 

[Andrew Gabriel]

This explanation confirms what I see with such lamps in cold weather. The
older the lamp, the higher the strike voltage and so the more likely it is
to flicker. Eventually, the energy from the flickering arc should warm the
lamp enough to sustain it without flickering (unless the lamp is at
end-of-life) so it would be interesting to hear from anyone who has watched
a flickering lamp for a while to see if that indeed does happen.

With the SOX I've seen doing this, the flicker is happening when fully
run-up. I haven't watched one of these during run-up, so I don't know
if it happens during run-up. Temperature wasn't low when this happened,
and I suspect that's not relevant.

I don't have a sample dead one with this failure mode (which isn't
common), so I can't inspect the lamp to see what visible failure
indication there might be. As a pure guess, I might speculate that
the emission material is sputted off the electrodes, and it can't
sustain an arc in thermionic emission mode. The 35W SOX has an
ignitor/starter which is probably repeatedly trying to start it.
The larger ones use a leakage reactance transformer to provide both
the starting voltage and current limiting, because the arc voltage
is too high for a simple series ballast on 240V, and so don't need
an ignitor/starter. I don't think I've seen the larger ones flashing;
when the emission coating wears out, they seem to fail to light up
at all (or with only a very dim glow around the electrodes which
you can't see from the ground).

IME more common failure mode of SOX is the arc tube develops a leak
and the sodium is ejected into the outer vacuum tube, where it often
forms an opaque mirror coating on the inside of the bulb facing
the ejection point, so the light no longer escapes through part of
the bulb (can block out most of it eventually). The arc tube seems
to be able to lose a lot of sodium in this way, yet still work, but
eventually it turns into a dim red neon light which never runs-up
(nicknamed a "red burner"), as there's no longer enough sodium left
in the arc tube, just the neon starting gas.

 

[johnwright]

Because of utility privatisation they don't service the lights, exchanging
blown bulbs with fresh ones?

I don't think they ever did. They did a planned maintenance thing which
was replacing all the bulbs whether working or not. I saw a private
contractor doing that the other day.

 

[James Sweet]

Someone mentioned that the cause of the flicker might be due to the
luminaire's photocell getting mixed signals due to reflection from the snow.
Photocells usually have a delay circuit built in; otherwise, they would
react to lightning flashes or headlight beams sweeping by.

TKM

Many photocells, particularly older ones, are thermal. The CdS cell
controls current flowing through a piece of resistance wire wound around
a bimetal strip. When sufficient light falls on the cell, the strip is
heated, it bends and opens the contacts. This inherently creates a
delay. Electronic photocells are designed with hysteresis for the same
reason, normally the delay is around a minute.

 

[James Sweet]

With the SOX I've seen doing this, the flicker is happening when fully
run-up. I haven't watched one of these during run-up, so I don't know
if it happens during run-up. Temperature wasn't low when this happened,
and I suspect that's not relevant.

Another characteristic of SOX is that the lamp voltage (and power
consumption) rise rather significantly over the life of the lamp. This
causes the same issue, eventually the voltage is higher than the ballast
can supply and the arc will become unstable and flicker. These things
usually fail due to either sodium depletion or the electrode seals fail
from the corrosive action of the heated sodium, but an older lamp
coupled with colder weather, especially if the ballast is a choke rather
than a leak autotransformer, they can do this instead. HPS lamps will
not restrike hot, so when they reach end of life they normally will
cycle, but SOX will usually restrike even hot, so they can flicker.

 

[MadManMoon]

Another characteristic of SOX is that the lamp voltage (and power
consumption) rise rather significantly over the life of the lamp. This
causes the same issue, eventually the voltage is higher than the ballast
can supply and the arc will become unstable and flicker. These things
usually fail due to either sodium depletion or the electrode seals fail
from the corrosive action of the heated sodium, but an older lamp
coupled with colder weather, especially if the ballast is a choke rather
than a leak autotransformer, they can do this instead. HPS lamps will
not restrike hot, so when they reach end of life they normally will
cycle, but SOX will usually restrike even hot, so they can flicker.

What most often happens is that the lamp shuts off completely, and then
restarts, which takes it just as long to pump up as before because the
run temp is far higher than the shut off idle temp, even if after only a
couple minutes.

I used to make a joke and said that I shut them off 'with my aura' all
the time because we often saw them shutting off as we approached while
out getting a buzz, back in 'the day'.