I've been reading for some time, the wonderfulness of "keeping the existing lighting" of various communities, streets, etc.  Especially lately, the debate over Wilshire Blvd. in LA.  Here in my hometown of Buffalo, NY, I've seen upgrades (sometimes two or three times over) on various streets and I understand the need to replace lights, poles, etc.  Three examples of this:

1. McKinley PKWY., the street where I grew up saw two upgrades (three if you include the changeover from Incandescent to 400 watt MV  before I was born) in my lifetime. The first was the changeover from 400-watt mercury (Westinghouse OV-25 Luminaires along with LM, GE, and T/B replacement lumes) to 250-watt HPS (CH OVM along with T/B, Cooper, and GE replacement Lumes) in 1986.  The second was a pole changeover to 14' Central Park style luminaires with 175-watt metal halide in 2004.

2. Cumberland Avenue-1985, replacing 6.6A series incandescent on 10' poles with 100-watt HPS (CH OV-15 Luminaires) on 25' Davit poles, and an upgrade to 150-watt HPS (Cooper OVZ) in 1999.

3. Grant St-Road reconstruction saw the replacement of 400-watt MV to 250-watt HPS (assorted GE, T/B, and CH lumes) upgraded to 400-Watt MH (CH OVX, GE M-400R3), and a repoling with Holophane 250-watt HPS teardrop lumes.

What I'm trying to get at is that it's not always a bad thing to upgrade, especially where energy efficiency, better lighting, or repoling when the old poles have deteriorated badly. 

Thoughts?

I can't say I'm too thrilled about the major high pressure sodium upgrade in the City of Pittsburgh in 2005, there were Westinghouse OV-25 Remote Ballast 400 watt mercs replaced with Cooper Lighting OVZ 70-250 watt high pressure sodium streetlights throughout the city.

Now the skies are even more polluted, not a very good trade off.

In the same city, I did see some General Electric M-400A2 200 watt high pressure sodium fixtures replaced with Holophane 175 watt metal halide teardrop lights but they're already having problems.

The Chief concern shouldn't be whether you can see the entire blanket of stars in the sky, but whether you can avoid that car that is heading towards you in whiteout conditions.  HPS light has the distinct advantage of cutting through fog and heavy snow.  As to the Holophanes, Someone needs to improve the QC at the factory.

Well honestly...I CAN'T see well under HPS....I actually see a lot better with MV or MH...or even CMH....but with HPS......things seem darker.....and colors don't look good......I have made more mistakes driving under HPS than under mercs or MH!

I'm just the opposite.  I guess it's because Buffalo started its changeout early (Mid 1970s) so I'm used to the light.

While it is true that light spectra in the redder regions cut through fog and other "whiteout" conditions due to the longer wavelengths, general night time illumination has to be "de-rated" because our eyes don't work as well under yellow to red in night time adjusted vision.

And because longer wavelengths are less easily reflected or scattered, the illuminated area also tends to be more shadowy. Even the dark sky website admits that due to the way we see at night, sodium lighting may actually lose some efficiency and metal halide gain efficiency v.s. the actual lumens-per-watt comparison. I would also speculate that mercury vapor may also benefit from this little-discussed piece of info. Although, this may only apply to very low light levels.

Here is more info to judge for yourself.

The problem with HPS is that their longer wavelengths travels much farther into the sky than the shorter wavelengths of white and blue light sources such as MH and MV. So with the increased lumen output of HPS lamps, you are setting yourself to more severe light pollution problems. There are lots of mercs on the freeway that runs through Simi Valley where I live, and they don't seem to have problems in fog nor rain. And since they are well maintained, most have bright lamps. HPS is still more efficient tho. Also everyone has their own preference in lighting.

I live in a mostly merc area...and I don't see orange sky as often.....the sky in my area at night looks more purplish white with some green and a very tiny HINT of orange......

But go to Chicago.....the sky is ORANGE like crazy! (gets better if you GET OUTTA CHICAGO and go to suburbs which is 99% mercs)

So HPS is no-no ......LPS is much better to use!.... Mercs and Clear Mercs and CMH are the BEST choices......

now imagin a cycling HPS light in front of your bedroom window........now how are you feeling?

Sure the road looks brighter in HPS....but I find more sad looking trees in HPS area than in merc area............if you go to the LA area where there's more incandescents and mercs (I watched Jeremiah's video) WOW it looked so 1950's with a LOT more TREES! Very green looking and more cheerful!

Also HPS isn't even natural color....I would accept White HPS.....

@Jace - I don't have to imagine. I had a couple sleepless nights because of a cycling HPS until I called the power company. I even asked them to leave the old bulb at my door but they didn't.

How did you ask them? If you asked on the internet...they def won't..........trust me......on the phone is same thing...because you are not contacting the Lineman HIMSELF.......trust me I can't really do that either.......I hope one day you meet a really nice lineman...