On 11/11/2015 13:04, MartinR wrote:

The recent post on light pollution reminded me that the reflection of street light off clouds,
typically sodium yellow or orange, has been becoming whiter recently,
no doubt due to the
proliferation of LED lighting. Even car headlights are becoming
whiter as xenon and LED become more common.

This from someone who lives south of Coventry. I'm not sure whether other local authorities
are moving over to less power-hungry lighting.

The ones moving from low pressure sodium to anything else are in for a
big shock. At upto 200 lumens per W the big orange yellow sodium Dline
based streetlamps are still the most efficient light source known.

White LEDs are getting closer to half that but at a much higher cost.

Big problem for astronomers is that sodium light could be more easily
filtered out at the telescope whereas broadband white light cannot.

LPS lighting is mandated where absolutely essential in the vicinity +/-
50km around major optical observatories (they prefer none at all).

--
Regards,
Martin Brown