"Brimstone" wrote in message
...
Paul Terry wrote:
In message
,
MIG writes

[ blue lights on street lamps]

A wild guess: maybe it's to do with distinguishing between power off
and the lamp failing?

That's possible, but I posted here a long time ago about new street
lamps on the South Circular that have a very distinct (and not at all
feint) blue lens pointing upwards.

This is very obvious from above, but can only be seen from ground
level if standing a very long way from the lamp post concerned.

If it is some sort of pilot lamp, it seems very badly positioned.

I didn't receive any plausible replies when I posted about this, but I
have seen it suggested that modern "cobra" street lamps are so well
designed to prevent night-sky pollution, that they need an upward
aspect in blue in order to delineate the location of major roads for
aircraft that, due to failure of automatic systems, are having to
rely on visual navigation at night.

Lit roads are perfectly visible even if you can't see individual lamps.
Besides, there are usually much better markers than roads - sports stadia
are very distinctive, for example.

....
Possibly they're markers for police and other emergency helicopters?

That sounds the most likely. They would want to know where the posts are
when trying to land on a road.

Colin Bignell

"nightjar" cpb@insert my surname here wrote:

Possibly they're markers for police and other emergency helicopters?

That sounds the most likely. They would want to know where the posts are
when trying to land on a road.

Hmm, which road in Camden Town do you think you could land a helicopter
on?

"Steve Firth" wrote in message
. ..
"nightjar" cpb@insert my surname here wrote:

Possibly they're markers for police and other emergency helicopters?

That sounds the most likely. They would want to know where the posts are
when trying to land on a road.

Hmm, which road in Camden Town do you think you could land a helicopter
on?

I don't know the area, but my local Police helicopter pilot reckoned he
could land his Twin Squirrel in an area about 15m wide and 25 m long. if he
really had to. Like most Police helicopter pilots, he was ex-military.

Colin Bignell

"nightjar" cpb@insert my surname here wrote:

"Steve Firth" wrote in message
. ..
"nightjar" cpb@insert my surname here wrote:

Possibly they're markers for police and other emergency helicopters?

That sounds the most likely. They would want to know where the posts are
when trying to land on a road.

Hmm, which road in Camden Town do you think you could land a helicopter
on?

I don't know the area, but my local Police helicopter pilot reckoned he
could land his Twin Squirrel in an area about 15m wide and 25 m long. if he
really had to. Like most Police helicopter pilots, he was ex-military.

http://maps.google.co.uk/maps?f=q&so...e=&q=camden+to
wn&sll=51.543693,-0.140076&sspn=0.005278,0.012424&ie=UTF8&t=h&ll=51. 5396
36,-0.142924&spn=0.002639,0.006212&z=18&iwloc=addr

http://tinyurl.com/az2oxc

It's not an area where I can see a helicopter landing in the street.

In message , nightjar
writes

"Brimstone" wrote in message
...

Possibly they're markers for police and other emergency helicopters?

That sounds the most likely. They would want to know where the posts are
when trying to land on a road.

You'd never land a helicopter on the road concerned. The south circular
in these parts is a narrow single-carriageway road, with buildings right
up to the pavement.

Also, most buildings are higher than the lamp posts - I can clearly see
the upward-pointing blue lights from my second floor because they are
just below window level. They are very hard to see from pavement level.

I wondered if they could be for aircraft recognition because we are
close to the spot where the Battersea heliport flight paths cross the
incoming Heathrow flight path, albeit at a lower level. But if these
lights are appearing in other parts of London, that would not be the
reason and, as has been pointed out, there is plenty of light diffusion
on main roads to see their positions from the air.

Given that the blue light is in the position normally occupied by the
dusk - dawn light sensor, I wonder if the blue glow is some way of
making the sensor more accurate in densely-lit areas?
--
Paul Terry