# Street and parking lot lighting



## RedLED (Feb 24, 2020)

I have noticed all over the country there seems to be Neutral 4000k LED street lights and parking lot lights.

Are there any standards for color Temp.? They sure look neutral to me. I have a color meter somewhere, I may do a test and find out.

Thanks,

RL


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## archimedes (Feb 25, 2020)

Hey Red, this topic would generally go in Fixed Lighting instead of Transportation Lighting.

I'd move it for you, unless you (or the Transportation mods) feel strongly otherwise.

Please let me know.


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## RedLED (Feb 25, 2020)

I was not sure where to post this, I thought since it involves transportation, this would be the place. It seemed the fixed lighting was more consumer and residential. I did think about it, and decided to go here.

I will leave it up to you, and the transportation guy's to decide.

Thanks,

RedLED


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## Alaric Darconville (Feb 25, 2020)

It's a combination of the two. They are fixed lighting, but they present benefits AND drawbacks where traffic is concerned.

Streetlights can be problematic in certain traffic situations; it would be nice if they were less intense, and tended less towards blue. They'd also contribute less to light pollution if they had a much warmer color.


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## archimedes (Feb 25, 2020)

Sounds like here is good


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## RedLED (Feb 29, 2020)

I lived in London, with my family years ago, and the street lights were the yellow sodium lights, and the were awful. The color of the Fire Brigade trucks shifted way, way off. Back here I don't like the cool or orange tint lights, the neutral seem much better. 

This forum has some real professional people here, and I would like to hear from them. 

Thanks,

Best,

RedLED


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## bykfixer (Feb 26, 2022)

A few years back, while managing a city block improvement project in a small town, the designers picked out decorative poles with "gas lamp" looking tops. The globes were opaque "eggshell" like color and the bulbs were halogen, which surprised me. I did not know street lights still used halogen in some cases.

To the pedestrian walking about they were supposed to cast a nice glow and were spaced close enough for motorists to see by under a 25mph speed limit typical of a city block with much foot traffic.

The designers scratched their head about lights at intersections though. Those were much higher above. Where the gas lamp looking numbers were about 20 above the road the corner lights would be around 50 feet above the ground. And were supposed to illuminate about 3 times the area.

What to use, they said. One guy said to me "you're a flashlight guy what do you think?" "Who me?" For some reason my brain asked "what do they use in Florida where all those sea turtles lay eggs?"

I used to hear Rush Limbaugh speak of having to turn off his beach lights at certain times of year. Some research later I had found a manufacturer and a model that would provide a broad lighting based on what is used in Clear Water Florida on main highways without much light pollution. A slab configuration of LED's with a cobra head top. The LED "lamps" are user serviceable too, so if one or more fails the owner can unscrew and replace like a light bulb. 

I picked 3700 kelvin to mimic those halogen lamps and an output that would not blind people who had been travelling on unlit country roads that intersect with that city block. CRI was listed as 85 so I figured it wouldn't look all funky like those shopping mall lights that make a green car look gold.

Funny thing is I've never returned to that town after dark to see how it turned out. The client indicated they were pleased with the results so I've never taken time to see for myself.


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## PhotonWrangler (Feb 26, 2022)

I think 3700k is a great choice for street lights as it will render all of the grayish-brownish stuff on the ground better than higher color temps.


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## jtr1962 (Feb 26, 2022)

PhotonWrangler said:


> I think 3700k is a great choice for street lights as it will render all of the grayish-brownish stuff on the ground better than higher color temps.


NYC began their streetlight replacement with 4500K, which I thought were a perfect balance between too yellow and too blue. Incidentally, 4000K to 5000K maximizes your peripheral vision. Anything yellower degrades it, anything bluer just doesn't improve it. So these lights were pretty much ideal for their intended purpose of seeing things.

Then some people started complaining. Most of it was about light trespass, which is easily fixed with cutoffs or different optics. Instead, the city started replacing the lights on some streets with ones which are not only lower wattage, but also yellower. They look to be around 3000K. I can't stand them. While they're still better than the HPS they replaced, the much lower apparent brightness, and yellower color which hurts peripheral vision, definitely compromises safety. I've been meaning to write to them about all this, in the hopes they'll change them back. At least they kept the 4500K ones on highways and major arterials. I'd even gladly take 3700K over these. Still a little too yellow, but not so much so as to cast a depressing pallor over the entire neighborhood.


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## idleprocess (Feb 26, 2022)

jtr1962 said:


> Then some people started complaining. Most of it was about light trespass, which is easily fixed with cutoffs or different optics. Instead, the city started replacing the lights on some streets with ones which are not only lower wattage, but also yellower. They look to be around 3000K. I can't stand them. While they're still better than the HPS they replaced, the much lower apparent brightness, and yellower color which hurts peripheral vision, definitely compromises safety. I've been meaning to write to them about all this, in the hopes they'll change them back. At least they kept the 4500K ones on highways and major arterials. I'd even gladly take 3700K over these. Still a little too yellow, but not so much so as to cast a depressing pallor over the entire neighborhood.


Not a big fan of the US market's ongoing obsession with mimicking incandescent spectrum myself, but impact of excess blue on circadian rhythm is very real. And while this can be mitigated to a degree with directing the light where it's needed - downward - there's still lingering effect. In areas with wildlife the impact on native creatures can be quite pronounced: used to be a metal halide streetlight in front of a prior family home across the street from a tree that blue jays nested in and they would _scream all night_ because of that streetlight.

Suspect that pretty much any reasonable CCT white LED will be a huge step up over sodium lamps' destruction of _visual cognition_.


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## jtr1962 (Feb 26, 2022)

idleprocess said:


> Not a big fan of the US market's ongoing obsession with mimicking incandescent spectrum myself, but impact of excess blue on circadian rhythm is very real. And while this can be mitigated to a degree with directing the light where it's needed - downward - there's still lingering effect. In areas with wildlife the impact on native creatures can be quite pronounced: used to be a metal halide streetlight in front of a prior family home across the street from a tree that blue jays nested in and they would _scream all night_ because of that streetlight.
> 
> Suspect that pretty much any reasonable CCT white LED will be a huge step up over sodium lamps' destruction of _visual cognition_.


There's actually one way around that-use high CRI for streetlights. Look at the spectra of very high CRI LEDs of any CCT. There is no pronounced blue spike. So for any given lux level you reduce the amount of blue light substantially.

Based on my anecdotal observations, another benefit of high CRI lighting is that the apparent brightness is higher for any given lux level. Or put another way, you can negate the lower efficiency of high CRI lighting by lighting to lower levels, still using roughly the same power as before, while not sacrificing apparent brightness.

The final issue has to do with peripheral vision. All other things being equal (i.e. CRI, lux), higher CCT (up to maybe 5000K) results in better peripheral vision. If you use a lower CCT light, you have to increase the lux to have the same level of peripheral vision. And doing so probably gives you at least the same amount of blue light as the higher CCT solution, perhaps even more. Or put more succinctly, the only way you can get away with reducing blue light content is by sacrificing safety due to reduced peripheral vision (assuming similar CRIs for both high and low CCTs). Using low CCT LEDs to supposedly solve the blue light issue then isn't a viable solution.

However, you can reduce blue light without sacrificing peripheral vision by going to very high CRIs. Strangely, it's almost dogma for outdoor lighting that CRI 70 or so is "good enough". Higher CRIs (95 or better) not only makes everything look better, but it reduces the blue spike, and lets you lower lux levels also.


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## Alaric Darconville (Feb 28, 2022)

bykfixer said:


> The globes were opaque "eggshell" like color and the bulbs were halogen


I sure hope those globes were translucent, else they'd have just heated up, having halogen bulbs inside.


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## idleprocess (Feb 28, 2022)

jtr1962 said:


> There's actually one way around that-use high CRI for streetlights.


While I can subjectively confirm with this after swapping the lights in my office from _{whatever}_CRI to 90CRI, pricing and availability may preclude this for large numbers of streetlights where the volume is apt to be orders of magnitude greater.


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## Lynx_Arc (Feb 28, 2022)

High CRI may not be the best for streetlights..... there are studies that claim bluish lights reduce suicide and crime. Not sure however how valid they are.


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## jtr1962 (Feb 28, 2022)

idleprocess said:


> While I can subjectively confirm with this after swapping the lights in my office from _{whatever}_CRI to 90CRI, pricing and availability may preclude this for large numbers of streetlights where the volume is apt to be orders of magnitude greater.


While true, if the streetlight industry moved in the direction of high CRI it's almost trivial for LED manufacturers to give them the volume. In most cases it's a simple change of phosphor.


Lynx_Arc said:


> High CRI may not be the best for streetlights..... there are studies that claim bluish lights reduce suicide and crime. Not sure however how valid they are.


Bluish lights can still be high CRI. CRI is independent from CCT.


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## idleprocess (Feb 28, 2022)

jtr1962 said:


> While true, if


Market seems to care about upfront cost, energy savings, longevity, and a given CCT in about that order.



jtr1962 said:


> it's almost trivial for LED manufacturers to give them the volume. In most cases it's a simple change of phosphor.


I believe it's relatively trivial to adjust _CCT_ based on phosphor mixture. But all the other variables are, well, _variable_ batch-to-batch: making an efficient, high-output, right CCT/CIE coordinates, high CRI final product has _yield_ challenges.


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## LEDphile (Feb 28, 2022)

idleprocess said:


> I believe it's relatively trivial to adjust _CCT_ based on phosphor mixture. But all the other variables are, well, _variable_ batch-to-batch: making an efficient, high-output, right CCT/CIE coordinates, high CRI final product has _yield_ challenges.


CCT and CRI are both tied to the phosphor mix (and pump wavelength), along with the target CIE coordinates. There is, of course, some manufacturing variation in the die and phosphor mix that leads to variations in the chromaticity coordinates, efficacy, and forward voltage of the LEDs, but these are relatively minor at this point. And any of the major LED vendors (and some of the less major ones as well) can sell you LEDs from within a 5 SDCM step ellipse around the target center point, and have that represent essentially the entire production distribution for that CCT and CRI.


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## JustAnOldFashionedLEDGuy (Jun 5, 2022)

Peripheral vision with street lights has little to do with CCT or CRI. You need that blue light. Your scotopic vision is sensitive up past 500nm, but you have more density of blue receptors in your peripheral vision.


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## PhotonWrangler (Jun 6, 2022)

JustAnOldFashionedLEDGuy said:


> ...you have more density of blue receptors in your peripheral vision.


That's striking. Does this mean that our color perception varies across the field of view?


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## John_Galt (Jun 7, 2022)

JustAnOldFashionedLEDGuy said:


> Peripheral vision with street lights has little to do with CCT or CRI. You need that blue light. Your scotopic vision is sensitive up past 500nm, but you have more density of blue receptors in your peripheral vision.



Off the cuff, that sounds like a more optimal driving experience would be mixing lower cct light directly forward, with higher cct light to the edges of the roadway. Selective yellow headlamps with cold(er) white cct lamps providing road-edge illumination duty. The opposite of a low beam fog lamp arrangement (although fogs are not part of the low beam and should not be used in clear weather at normal speeds).


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## JustAnOldFashionedLEDGuy (Jun 7, 2022)

John_Galt said:


> Off the cuff, that sounds like a more optimal driving experience would be mixing lower cct light directly forward, with higher cct light to the edges of the roadway. Selective yellow headlamps with cold(er) white cct lamps providing road-edge illumination duty. The opposite of a low beam fog lamp arrangement (although fogs are not part of the low beam and should not be used in clear weather at normal speeds).



This has been discussed in the realm of street lights. Central vision which is what you see looking head is photopic/mesopic and hence why even HPS is pretty good at higher speeds. At low speeds where peripheral vision more comes into play, the higher CCT/more blue is beneficial. @PhotonWrangler, our color perception is predominantly central vision. It exist in the periphery, but resolution is obviously not great. I am not aware of any change in perception of colors in the periphery.


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## Alaric Darconville (Jun 13, 2022)

Night driving conditions don't use photopic or scotopic vision, rather mesopic vision.
Blue light may let you see some motion in the periphery but that's about it. Remember, blue light just doesn't work well with our optical system.

That higher-CCT light going off the edges of the roadway may be disadvantageous when you look directly into that illuminated field, and I'm not sure that's worth any advantage you MIGHT get seeing some defocused motion off to the side.


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## JustAnOldFashionedLEDGuy (Oct 4, 2022)

John_Galt said:


> Off the cuff, that sounds like a more optimal driving experience would be mixing lower cct light directly forward, with higher cct light to the edges of the roadway. Selective yellow headlamps with cold(er) white cct lamps providing road-edge illumination duty. The opposite of a low beam fog lamp arrangement (although fogs are not part of the low beam and should not be used in clear weather at normal speeds).



Sorry not been here for a while. This has been discussed over the years on/off in IES circles, and I remember it rearing its head w.r.t. adaptive headlights, but I have not kept up on where that has gone. Alaric or Virgil would be far more up to date on discussions in automotive.

However, it would be best to not talk blue and CCT, and talk rod and cone stimulus. You can achieve significant rod stimulus, hence providing enhancement to periphery and vision at lower levels, while not stimulating blue cones for glare, but you are stuck w.r.t. circadian stimulation because there is too much overlap between IPRG cells and rods w.r.t. stimulus spectrums. The light levels for street lighting (residential) do reach well into the lower ends of mesoptic. You can maximize rod stimulus w.r.t. IPRGC stimulus at around 530-535nm which narrow spectrum will not stimulate blue cones. You run into practical issues. Monochromatic LEDs at that wavelength have poor efficiency. Phosphor converted lime has pretty good efficiency, but does have spectral leakage.


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