Streetlamps again - Na lamps changed for LED type

[chiltonstar]

My observing site (aka garden) has two visible streetlamps to the north, one at 50 m and one at 115 m. In summer, these are bearable but without leaves in winter cause quite a lot of LP. Both were sodium lamps until a few days ago, when one (at 50 m) was changed for an LED type lamp, so-called warm white I believe. Visibly, there is a lot less light pollution and the garden is very much darker. I took a phone image last night with a transmission grating taped over the phone lens to show the relative brightness of the two lamps, and a coarse spectrum showing where the light energy is concentrated (uncorrected for spectral response). 

In the image, the LED lamp is relatively dimmer despite being less than half the distance of the remaining sodium lamp. More worryingly, it's obvious how much of the LED's output is in the blue, which will cause scatter in hazy conditions (blue light scatters more that orange) so I suppose in due course, I may get less LP but may perhaps see more background scatter when conditions are less than perfect.

LED lamps are being blamed for a dramatic effect on UK's moth population because of this blue emission (moths only see blue light) - some councils have dealt with this by fitting yellow filters over the lamps. They get the added bonus too that the lamps don't get coated with flattened mozzies.

Chris

Edited March 4, 2022 by chiltonstar

[Zermelo]

4 hours ago, chiltonstar said:

some councils have dealt with this by fitting yellow filters over the lamps

Do you happen to have a reference for this, Chris?

[chiltonstar]

4 hours ago, Zermelo said:

Do you happen to have a reference for this, Chris?

I'll try and fish it out. It's one I found three years ago when I was writing the light pollution section for a local plan. May have been Gloucestershire or Gloucester, plus several others.

Chris