(quote)
Sodium is easier on your eyes at higher levels than Metal Halide. By higher levels I mean Photopic Vs. Scotopic vision. The jogging trail is lit at Photopic levels using a bluish light source that performs better at lower (Scotopic) light levels (think pre-dawn light).
I respectfully disagree....
While technically what you say may be true, my overall perception says different...
If I have been driving in sodium light for a while and then arrive to a place like DT Dallas where it is lit with Metal Halide, and my eyes and my psyche seem to have a weight lifted off of them ...
Instantly things are recognizable and the light seems to agree with life itself, similar to sunlight color and looks more natural...
Same driving around interchanges in Tulsa where sodium is on the lower cobraheads on the highway stretches and the exits are lit with MH tower lights (which are sodium fixtures re- fitted with MH due to vibration issues with the HPS ceramic arc tubes) and there is the same relief when you go into the white light ...
(quote) Metal Halide is 3-4 times more likely to cause skyglow than Sodium because of the way blue light scatters in the atmosphere. This is more of an environmental, biological or eco-tourism concern, but if you wanted a clear night sky, Metal Halide would be a bad choice.
I think a clear night sky in the city is not a likely scenario since this is a free country and people and companies can light their property, and will, no matter how ugly ... Even if I personally do not like the looks of someones lighting scheme (and I HATE the shotgun approach to lighting for the record) My only recourse is if they trespass light onto my property without my permission...
(quote)Despite Sodium's orangish color, the light can evoke a more warm and inviting feeling than the coldness of Metal Halide (an important point for architects).
I am not sure where you are getting your info from or what metal halide lamps you are looking at, but the metal halide lighting I have seen is not like the 80s bluish MH but VERY warm almost incandescent in appearance and not blue at all...Look at some spectrum charts of new color MH and see just how much better and fuller the spectrum of useable light is...
(quote) You get more Lumens-per Watt with Sodium than Metal Halide,
If you were thirsty, even VERY thirsty, would you prefer a glass of clean, clear water to drink, or a gallon of dirty water to quench your thirst...
I'll take a lower light level of quality lighting than a higher nember of unuseable lumens anyday..
think "glass of clean water"
as opposed to "bucket of dirty water"...
And last but not least, Sodium is the choice for streetlighting because the lamp life is twice that of Metal Halide, which translates to better maintenance economy (have to change them only half as often).
Not entirely true without a few comments...
HPS (orange) starts out with a golden white appearance and in some situations it is just barely tolerable and only sometimes pleasant...
since most outdoor lighting is relamped only when is goes out, HPS is allowed to go on living after it turns an obnoxious pinkish color for a long time til it dies...
MH indeed has a lesser lifespan but also should be replaced before it actually dies for the sake of light output and color...
However, the new (somewhat of a breakthrough) pulse start (and most lower wattage MH lamps already are) lamps have longer life and more stable color and lumen output...
In my opinion it is more likely a third less useable life and I would gladly replace lamps more oftem (slightly) and have quality lighting than a lot of light that is poor quality...
Woodland Hills started out with 1kw HPS fixtures in the 70s and changed out everything a number of years ago and the facility has a much more pleasing appearance now, than then, even if a lot of light is wasted through too high wattage distribution, that's another rant...
Walgreens @ 31st & Harvard recently changed out all HPS to MH and what a difference on how appealing the area without increasing wattage and maybe even lowering light levels...
They just changed the color..
But in2neon is correct that most high-intensity light sources are brighter in their first 100 hours (initial Lumens) than the rest of their lamp life (maintained Lumens), including Fluorescent lamps. How much their
intensity depreciates depends on the type of lamp.