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.

I have no idea whether this is true (despite quite a lot of fruitless
research), but I have noticed that most of these upwardly-directed blue
lights are on major trunk routes in the capital (specifically on TfL red
routes).

All of the new red-route lamposts around here also have two brackets,
about two metres apart vertically, with eyes that seem to be designed to
tie banners. No banner has ever appeared - if the only one that ever
does is "London Olympics 2012", I shall be even more despondent about
the hidden costs of "the games" - an awful lot of welded steel has gone
into these appendages.
--
Paul Terry