I still don't understand this trend of replacing the sodium lamps with LED. The sodium lamps use roughly the same amount of energy, cast a light quality that is better for both humans and animals, and are already there, saving a bunch of money in doing replacements.
Why are all these cities undertaking huge renovations to go to LEDs?
Why would LEDs put Sodium vapor lights out of business?
Sodium lamps have the worst color rendering of any bulb. They produce a dark yellow glow which is generally a very low quality light. Additionally, there are serious waste disposal issues with sodium lamps. In particular, they have been known to start fires in the event that the lamp is broken and the sodium metal is exposed. The sodium can catch fire even in the event that the lamp is broken on the ground. For this reason it is safest to break sodium lights under water and then to subsequently dispose of the destroyed bulb. Lastly, HPS and LPS lights are monochromatic, so they can mess with your color vision if you look at them for an extended period of time.
Perhaps more importantly, in the last few years LED efficiency has surpassed that of even LPS and HPS lights and its efficiency improvements are progressing at a much more rapid rate. The largest selling point of LPS and HPS lights is the cheap selling price, the high energy efficiency (low operating costs), and the relatively long lifespan. LPS and HPS still retain these advantages over most conventional bulbs but they lose on all three counts to LEDs. In some areas (e.g. lifespan) they are drastically inferior to LEDs. The extremely low maintenance and replacement costs with LEDs is actually a major cost benefit over the long term. LED lifespan can be greater than 100,000 hours (more than four times that of LPS or HPS). Having to purchase one bulb versus 3 or 4 bulbs over the course of time is a significant selling point for LEDs. The bottom line is that having lost their traditional advantage of being the most energy efficient bulb on the market, there’s very little reason to use a sodium vapor light when LED lighting is available.
Just wanted to point out that the choice municipalities have made for street lighting is not really an LED technology limitation as much as different evaluation criteria.
For example, while sure, OSRAM advertises/sells street lighting LEDs that are broad spectrum (131 lm/W) [1] they also sell single-color LEDs like these amber ones that are actually even more efficient (141 lm/W) with an emission range almost entirely within 600-640nm [2].
This is almost as tight a range as LPS (which looks like about 580-610nm) [3], and it beats out HPS considerably [4].
This was a big deal in Tucson for a while. It used to be that there was a city ordinance that mandated public outdoor lighting was all sodium lamps because it was super easy for the local observatory to filter out that one frequency of light.
Warm white LEDs exist, with color quality exceeding that of sodium vapor in every way, but cities often use blueish LEDs because they're cheaper and more efficient.
As a person who has spent a decade as an amateur student of human color vision, let me state emphatically that “color quality” is a horrifically bad criterion for choosing nighttime street lamps. Nobody should be trying to read a book or critically evaluate photographs in the middle of the road at 3AM.
Street lamps should include as little short wavelength light as possible and should otherwise be as even (this means: use more lamps spaced closer and placed at lower height, diffused and shielded from the side) and dim as possible, so as to avoid causing distracting glare in people’s peripheral vision, and avoid causing high contrast between areas directly under the lamps and areas in shadow. Human vision is amazingly good at adapting to very low light levels. After adaptation, humans can navigate the environment by e.g. starlight, but at any rate can see just fine under sodium lamps.
But the way cities roll out LED street lighting is to put a small number of widely spaced very intense blue lamps high up in the air, not diffused and with little shielding from the side.
Every parameter has been optimized (pessimized?) for blasting away people’s night vision and causing enough glare to make seeing into the shadows all but impossible.
Extremely low color temperature LEDs would be fine, but don’t really have any especially great advantage over sodium lamps. (Except maybe for getting some government subsidy money?)
I thought the wider spectrum of light coming from LED streetlamps means they can be run at a lower brightness to provide the same visibility, which means less overall light pollution (less reflection back upwards) and less power usage.
The little wild creatures don't appreciate that visibility. If the recent report on biodiversity loss bothered you, avoiding LED outdoor lighting is one easy action to take locally.
There's not a lot of biodiversity on the streets anyways, so that's not a big deal. but the little wild creatures do appreciate less light in the woods, which is what you get from less light pollution.
> For this reason it is safest to break sodium lights under water [...]
This sounds like dangerous advice. Sodium reacts exothermically with water producing NaOH. In practice this means it will violently boil and splatter strongly alkaline lye around. (Source: this is how my high school chem prof lost some of his eyesight.)
The City of Chicago is funding a replacement of all it's sodium bulbs with LEDs solely off the energy cost savings [1]. I'm unsure what sodium lamps you're referring to that use a similar amount of energy as LEDs.
> The sodium lamps use roughly the same amount of energy
"The new LED lights will consume 50% less electricity than the existing High Pressure Sodium (HPS) lights. When fully implemented the new fixtures are estimated to save the City $10 million a year in utility costs. By consuming less electricity, the City is helping reduce its carbon footprint. LED fixtures last up to two-three times longer than HPS fixtures."
> cast a light quality that is better for both humans and animals
"Compared to HPS lights, LED lights make it easier to see the contrast between an object and its surroundings; so one can quickly and more accurately identify people, vehicles, road debris or other things on the street or sidewalk. The whiter light also enhances peripheral vision and improves the quality of video resolution"
> The new LED lights will consume 50% less electricity than the existing High Pressure Sodium (HPS) lights.
Not sure how they're going to achieve that. LEDs produce 37 to 120 lumens/watt, HPS and LPS produce 50 to 160 lumens/watt. The sodium lamps lose out only because they are omnidirectional and a mirror is required to aim their light down, so some of the light is blocked by the lamp itself. But overall LEDs don't save 50%.
> Compared to HPS lights, LED lights make it easier to see the contrast between an object and its surroundings;
This is true, but it's a red herring. While that might increase safety in one regard, the light cast by an LED is very blue, which affects both humans and animals, making their bodies think it is still daytime. This disturbs the natural hunting and migration patterns of the animals, and more importantly, disturbs the sleep of the humans.
Sleep deprived humans are for more dangerous than ones that have a harder time detecting object edges.
Also, shouldn't we consider quality of life issues when making these changes, and not just efficiency?
The availability of cheap overkill LEDs is making cities worse... It's especially noticeable when walking at night in areas with restaurants and nightlife.
It's not just street lightning, but also private buildings (maybe they're after that prison yard look?) and cars (giving pedestrians and drivers free lasik, nice!).
Maybe these are OK for highways, but this sucks big time for everywhere else.
They are just as terrible for highways. Getting hammered by blue glare in your peripheral vision is very distracting and destroys night vision, making it harder for drivers to see.
(For the same reason, LED car headlamps are horrifically bad for everyone other driver on the road.)
I don’t understand why there aren’t isn’t strict enforcement of laws about headlights yet. Do the police and politicians not see the danger themselves in the rear view mirror when they drive on the road?
> Do the police and politicians not see the danger themselves in the rear view mirror when they drive on the road?
They don't realize there's a problem, or they've just spent a lot of money "upgrading" their vehicle fleets and don't want to consider that they've been ripped off.
The vehicles of my local police departments and state highway patrol have had all their safe incandescents replaced with blinding LEDs. Flashing blue LEDs on the roof of the cars, flashing blue-white LEDs mixed in with the flashing red and blue LEDs, and blinding amber LEDs to warn of road hazards. The vehicles have blue-white spot lights, and sometimes they have blue-white light bars on to blind everyone within a quarter mile of the scene.
I think the police officers think their new lights are cool.
OSHA [0] should intervene, but I don't know that I can make a complaint on the police officers' behalf...
> Not sure how they're going to achieve that. LEDs produce 37 to 120 lumens/watt, HPS and LPS produce 50 to 160 lumens/watt. The sodium lamps lose out only because they are omnidirectional and a mirror is required to aim their light down, so some of the light is blocked by the lamp itself. But overall LEDs don't save 50%.
I did a quick search and found their RFI [1]. They are reducing electricity consumption by 50% because they are replacing 40+ year old light fixtures that have 70+ year old wiring:
> In the 1950s, the City installed new lighting infrastructure citywide; utilizing mercury vapor lamps. In the 1970s, the City performed a system-wide lighting upgrade; replacing the mercury vapor fixtures with high-pressure sodium fixtures. This project was only a lamp head upgrade; the City retained the 1950s era electrical poles, wiring, and infrastructure. Over the years as underground wiring has failed, City crews have often replaced underground wiring with aerial wiring. In 2009, using available federal funding, the City replaced high-pressure sodium streetlight fixtures with more energy efficient ceramic metal halide fixtures along Western Avenue and Lake Shore Drive. That fixture replacement undertaking did not include upgrading the electrical infrastructure.
Nobody is going to “on the fly configure” color temperature of street lamps. It would add cost and complexity, be less energy efficient, compromise longevity, and is not a worthwhile feature in that context.
In practice, all “white” LEDs (even the very warm ones) consist of a blue LED + a yellow phosphor, and for efficiency reasons in contexts like street lamps the phosphor is never set up to absorb all of the blue light, which means that the intense blue glare inevitably is there clobbering people’s night vision.
It would be possible to make LEDs appropriate for street lighting, but the lighting industry does not currently sell them.
That's ONE way to make white LEDs. Another, more expensive but much better way, is to use an RGB LED and tune the driver to emit the color you want from the triad.
They're getting cheap enough now (insanely cheap, in fact) that it is now feasible to fit street lamps with them.
Imagine the use that could be had if you could change the color of street lamps on demand. Guide vehicles in an evacuation, direct police to a particular location by coloring a lamp red, or something. Direct ambulance by coloring a lamp blue. I don't know. Seems like it could be useful.
It's less about the LED being suitable for street lamps than it is about the lensing chosen to direct the light to the proper locations under the lamp.
> more expensive but much better way, is to use an RGB LED
This is better for displays (or maybe stage lighting, art projects, fancy effects, ...) but not better for standard room lighting, and definitely not better for street lamps.
Using street lamps as information sharing devices makes a cute 1 minute demo, and sounds cool to sci-fi fans, but in practice would be gimmicky and not very effective.
The actual light coming out of “RGB” LEDs necessarily has a quite spiky spectrum, because they overemphasize supporting a wide color gamut. They also include more short wavelength light than is desirable for nighttime use (compromising night vision). e.g. https://cdn2.goughlui.com/wp-content/uploads/2015/12/hue-def...
> It's less about the LED being suitable for street lamps than it is about the lensing chosen to direct the light to the proper locations under the lamp.
I’m not quite sure what you are trying to say with this bit. For best lighting, there would be more lamps spaced closer together, placed at lower height, orange in color and individually dim, and diffused and well shielded from the side. These are all features which would be helpful for any type of lamp.
Unfortunately, the LED streetlamps adopted by cities are high up, widely spaced, much too blue, extremely intense, and not shielded from the side.
The color rendering index of low pressure sodium bulbs is vastly inferior to that of a typical white LED. High pressure sodium bulbs are even worse in that regard.
For backlighting LCD screens, sure. But for street lighting, I don't want a good CRI. I want to minimize blue light, harsh shadows, and glare. The old yellow sodium lights were nice. The new LED streetlights around me are terrible.
A new supermarket by me installed all LEDs for the parking lot, and used warm white ones. You wouldn't even be able to tell they aren't incandescent without looking. I really hope more word gets out to not use "bright white" LEDs for outdoor lighting.
It depends on the type of sodium lamp. High pressure sodium bulbs emit light in an extremely narrow bandwidth around 589.3 nm, earning them a color rendering index of -44 (out of 100). Low pressure sodium bulbs broaden this range enough to earn a CRI of 24. These are the peach colored ones you are familiar with.
That's exactly why the light quality of sodium is better. Because at night you want yellow lights so you don't screw up the sleep patterns of both humans and animals.
It's generally my experience that street lighting is not very helpful while driving. It often reduces the contrast ratio between an object illuminated by my headlights and the background as well as the light fixtures themselves being a source of glare.
I'm not sure if that's serious, sarcasm, or reducto ad absurdum. Regardless, I've actually looked in to published research on the matter in the past. I don't have links to studies handy, but here's what I remember finding:
Street lighting does not reduce car-car collisions, and in most conditions, does not reduce collisions at all. The major exceptions were pedestrian crossings without traffic lights, and when illuminating curves or obstacles. I don't recall finding a comparison between overhead street lighting and reflectors or marker lights for curves and obstacles, but it seems to me those might provide the same benefit with less glare, energy consumption, and light pollution.
LED lights are now common in suburbs as they sprawl into habitats. Migrating birds get confused as they fly over cities. Coastal cities and towns mess with aquatic animals.
My guess is LED lights are supposed to last a lot longer. The human cost of replacing lights is probably a lot more than the cost of the bulb. Labor is expensive.
Not really. The rated life of sodium is 24,000 hours, and LED is 25,000. With a lot of money you can get LEDs with rated life up to 200,000 hours, but that's not typically what cities are buying.
That's just the average rated life of an LED street lamp. But if you do that math, that's about 5.7 years at an average of 12 hours a day. So these lamps were probably rated closer to 50,000 hours. You can also get sodium lamps that last that long. It's just an average.
Not all are. In the county I live in, they are still using sodium lamps. The one exception I'm aware of is a pilot program at a commuter parking lot, where they use LED lamps.
Why are all these cities undertaking huge renovations to go to LEDs?