What colour should streetlamps be?

[DaveS]

It's not just a matter for astronomers.

The huge light pollution caused by streetlights is very bad for any wildlife in the area, as well as messing with our circadian rhythms. Especially harmful is the horrid blue spike of unfiltered "white" LEDs

The sooner we realise that we are diurnal creatures who need darkness at night the better.

[GunZenBomZ]

Many councils have already started doing that. Not sure if yours has started yet but it looks like they have plans to if they haven't already

https://new.devon.gov.uk/streetlighting/part-night-lighting/

Great link & I'd hope more councils see sense with regard to turning off lighting. Only towns require localized lighting as they attract more people  for events & do's. Villages & outlying areas need to be darkened & the quicker this takes place the better it will be for nocturnal creatures & wildlife in general with the knock on effect of helping night-time hobbyists.

[pipnina]

Great link & I'd hope more councils see sense with regard to turning off lighting. Only towns require localized lighting as they attract more people  for events & do's. Villages & outlying areas need to be darkened & the quicker this takes place the better it will be for nocturnal creatures & wildlife in general with the knock on effect of helping night-time hobbyists.

Not sure whether those are in effect yet... Here in Plymouth we definately don't have dimming periods or even off periods for any of our street lamps and we're in devon. Although... Plymouth city council is seperate...

Exeter doesn't have its own council, does it? I'll have to ask my sister if the street lamps turned off/dimmed there.

[FenlandPaul]

Thanks Paul, that would be interesting to know.

RE: stage lanterns, only the cheapest use bare RGB, it's increasingly common to add white, for pastel shades and / or amber for better warm colours. Some go to RGBAW, and there's a new trend for adding "UV" which is actually just 405 nm violet, to give better deep blues (Congo Blue for those who know). ETC use up to 7 discrete colour LEDs in their top end (ie. expensive!) lanterns.

Sorry to take this OT!

OK so I spoke to one of our engineers today.  An RGB mix was an approach that was played about with in the very early days of white-light LED.  However there were three key problems.  Firstly, different coloured LEDs require different forward voltages, so optimising the drivers is very difficult - you get a much more efficient system by driving the same "flavour" LED chip, and it's been efficiency and reliability that has driven the LED revolution.  Secondly, you require a lot more LEDs to get the same lumen output.  This drives up the cost and so isn't very attractive to manufacturers.  Thirdly, the LEDs would need to be placed very close together for the light output to appear white, particularly if the lights are in low-ceiling applications.  Otherwise the eye will perceive the three individual colours and it would give a very unsatisfactory feel.   This creates manufacturing challenges. This can be overcome by projecting the light onto a surface, but that would lead to a significant loss in usable lumens.  Since lumens per watt is so important to the manufacturers (or, more specifically, manufacturers' marketing departments!!), it's not really a viable option.

Hope that helps.  All comes back to proper control and proper direction.

Paul

[DaveS]

Thanks Paul

I thought it might be something like that.

Stage lanterns need the LEDs to be very close together to get good blending without multi-coloured shadows, Chip-On-Board being one solution, where all the LEDs are mounted on the same small (Ceramic?) board.

[bitnick]

Talking about efficacy (lumens per watt, lm/W), did you know that the sun is about 95 lm/W? Or that the theoretical maximum efficacy for any light source, regardless of technology, is about 310 lm/W (for white light at about 5800 K and a colour rendering index of 93 - for monochromatic light at the peak of sensitivity of the human eye, 555 nm "laser green", it's 683 lm/W).

 

This is the point at which all incoming energy is converted into useful photons.

 

All of this from an article called Spectral Extravaganza: The Ultimate Light on Tom Murphy's site Do The Math. Well worth a read! (It even mentions the color temperature of Sirius and Rigel! )

Looking at current top-of-the-line white LEDs, they are somewhere around 130 lm/W (see eg Luxeon Star Rebels). Quite amazing really - we only have one doubling of efficacy left before it's as good as it gets!

[beamer3.6m]

Why are street lights not red.

[D4N]

Why are street lights not red.

Noes don't suggest that!

Peak emission would likely be 656nm wiping out any chance of seeing any nebulosity

[DaveS]

630 nm LEDs are much more common as well as appearing brighter. Whether they are far enough into the red not to affect the rods is another matter.

[pipnina]

Well, I've found out that Plymouth (where I live) is doing the same thing as the rest of Devon... Sort of.

They are replacing every street lamp with the new LEDs http://www.plymouth.gov.uk/ledstreetlighting.htmThis is, as expected, mostly to save money in the long run but it seems like it'll be beneficial, although not quite as good as what's happening to the rest of devon.

It's been stated that only street lamps on main roads will be dimmed, and there will be no switch off period unlike with the rest of devon. But considering it's the non-residential city centre (which is pretty much one large main road) that is the biggest source of glow for 30 miles, it's probably going to get lamps that have less light spill and are going to be dimmed. thing is they're replacing them slowly but surely. Perhaps I'll make a time-lapse video with my camera with a shot taken every friday... That should map the LP change very well.

Hopefully more councils across the country will 'see the light' _{I'm so sorry}

    ~pip