Cobrahead Streetlights: Cutoff or Non-Cutoff?

[KEK Inc.]

Non-Cutoff General Electric M400


Semi-Cutoff AEL 125
(Photo Cred:  MdCastle)

Full-Cutoff General Electric M400


(General Electric M400s and AEL 125/A325s use a very similar design.)

[Duke87]

Sodium vapor lighting in any fixture is disgusting. There are several newer technologies that give whiter light and use less energy.

[KEK Inc.]

Sodium vapor lighting in any fixture is disgusting. There are several newer technologies that give whiter light and use less energy.

I feel like they do a better job lighting things up.  The new LED lights don't light up nearly as much -- at least in Seattle.  I feel much safer walking down a street at night with sodium vapor lighting than LED lighting. 

Crime in the University District of Seattle has increased since Seattle has switched most residential streets to LED lighting.  Doesn't necessarily have to be the cause of the crime rate increase, but I wouldn't be surprised.  Dim streets can definitely increase the threat of crime.

[myosh_tino]

I feel like they do a better job lighting things up.  The new LED lights don't light up nearly as much -- at least in Seattle.  I feel much safer walking down a street at night with sodium vapor lighting than LED lighting. 

I noticed the new LED lights were significantly dimmer than the old sodium vapor streetlights.  I thought it was just me...

I'm guessing that the relative dimness (is that even a word?) was the main reason why cities were allowed to switch back to a whiter streetlight.  I remember, back in the day, streetlights were bright and produced a white light but because these lights interfered with the Lick Observatory on Mt. Hamilton, cities were required to switch to sodium vapor.  The orangish sodium vapor light apparently doesn't affect the observatory as much.

[KEK Inc.]

I noticed the new LED lights were significantly dimmer than the old sodium vapor streetlights.  I thought it was just me...

I'm guessing that the relative dimness (is that even a word?) was the main reason why cities were allowed to switch back to a whiter streetlight.  I remember, back in the day, streetlights were bright and produced a white light but because these lights interfered with the Lick Observatory on Mt. Hamilton, cities were required to switch to sodium vapor.  The orangish sodium vapor light apparently doesn't affect the observatory as much.

The cities around Lick Observatory (and other observatories in the U.S.) were asked to use low pressure sodium vapor lamps.  San Jose, and many of the surrounding cities use them.  The big island of Hawaii and San Diego uses them as well for the observatories. 

  Here's an American Electric Lighting SP2 lamp. 

American Electric Lighting SRX (used for residential usually). 

High pressure sodium vapor lamps have been a thing for a while, and Lick observatory wouldn't like them even though CalTrans uses them on all of the freeways.  (Intersting enough, you can see some low pressure sodium vapor Philips lamps in San Diego freeways).  Many cities including Cupertino, Milpitas, Downtown San Jose, Santa Clara, etc. use high pressure sodium vapor lights.  Now with how big the South Bay has sprawled, it's irrelevant since the light pollution is bad.  In fact, most cities in the country have used high pressure sodium vapor lamps for the past 40 years. 

That said, mercury vapor lamps are still used, even with cobraheads in some areas.  They're more prevalent on rural properties.  Mercury, when vaporized, emits a more white-blue light, and it was common from 1948-1970.  Our lovely controlling government banned sales of mercury vapor light fixtures in 2008.  It will be illegal to sell bulbs in 2016. 

[Duke87]

I'm guessing that the relative dimness (is that even a word?) was the main reason why cities were allowed to switch back to a whiter streetlight.  I remember, back in the day, streetlights were bright and produced a white light but because these lights interfered with the Lick Observatory on Mt. Hamilton, cities were required to switch to sodium vapor.  The orangish sodium vapor light apparently doesn't affect the observatory as much.

The reason observatories like sodium vapor is because it only emits one specific wavelength of light in the visible spectrum, so it's very easy for the telescopes to just filter out.

As for dimness, it's interesting: LED lights do produce fewer lumens than other technologies, however because the light is of better quality they allow people to see just as well with less of it. The reason they appear dimmer with streetlights is because LEDs are rather directional - unless countered with lenses or whatnot, they don't spread light over as wide an area as metal halides do, so changing the lights over if not done properly can create dark spots where they previously didn't exist.

Even still, LEDs are the big sexy thing that lots of people are looking into and they get all the attention - but there are other altenrative technologies out there that can be used for street lighting which do not have the directional problem and I would argue are better suited for the application: induction lighting (which is not a new technology), electronically-ballasted high intensity discharge (EHID) lighting, and light emitting plasma (LEP). Particularly the latter two.

[KEK Inc.]

It is interesting that there are no lens for LED lights.  I think it would spread it better.  It's blinding to look at directly, but the light does not really spread out.

The biggest problem with LEDs for Road equipment are that they don't produce substantial heat to melt ice build up.  I don't see it being a big problem with street lights too much; however, it's an issue with traffic signals.

[Scott5114]

Funnily enough, that's one of the two major reasons for switching to LED–the reason LEDs use less energy than incandescent is because LEDs do not waste as much energy as heat as incandescents do.

[KEK Inc.]

Funnily enough, that's one of the two major reasons for switching to LED–the reason LEDs use less energy than incandescent is because LEDs do not waste as much energy as heat as incandescents do.

In the long term, you break even on total cost in colder areas.  You have to hire people to clear ice from traffic lights during the cold season.  LEDs have a high initial cost; however, the low energy and low maintenance makes them worth it.  Plus, if a diode fails in a traffic signal or streetlight, the light as a while will still be functional.

[roadfro]

The City of Las Vegas has been on an aggressive push to change out high pressure sodium vapor cobrahead street lights with LED cobrahead cutoffs. It was a jarring change when I came home from Reno in June and they'd changed out to LEDs on my residential street (where there is only lighting at intersections), as it did seem much darker at first. Then I realized what Duke87 about the light being directional instead of glowing outward from all directions of the cobrahead bubble. In any event, Las Vegas' main arterial streets are still lit quite nicely, although I think they are using a brighter LED fixture on the arterial streets.

I think Henderson has used induction lighting in a cobrahead housing since at least this time last year. I haven't really driven between the two enough to see the difference in light output at night.


Reno has changed out cobrahead fixtures affixed to traffic signal poles only, not starting a wholesale changeout just yet.

On some recent projects in northern Nevada, especially the I-80 project through Reno-Sparks, NDOT has changed out standard cobraheads to LED cobraheads. Most of the new signs along that stretch are unlit, but those that are lit--due to size (the APLs at US 395) or being on curves where the sign isn't adequately lit by headlights--are lit from above using LED fixtures instead of HPS bulbs.

The biggest problem with LEDs for Road equipment are that they don't produce substantial heat to melt ice build up.  I don't see it being a big problem with street lights too much; however, it's an issue with traffic signals.

The fix there, or at least a considerable help, is to use 3/4 or cutaway visors on the signal lenses. You also presumably get the bonus of the visors costing less due to using less material.

[KEK Inc.]

NDOT has changed most of the lights in Carson City and the Nevada side of So. Lake Tahoe since 2010.

Again, I don't see why they don't use them on normal adjusted cobrahead fixtures with semi-cutouts.  I believe Hubbell actually made an LED model of its high pressure sodium RLC fixture.

A standard Hubbell RLC Cobrahead:


Here's actually a standard Hubbel RL Cobrahead (used for residential roads usually) with a LED retrofitting.


Slap on a convexed dome and I would support LEDs more.

@ Roadfro:  The visors wouldn't help in that situation.  The snow was blowing horizontally, and it stuck to the road signs as well.

[cpzilliacus]

San Jose, and many of the surrounding cities use them.  The big island of Hawaii and San Diego uses them as well for the observatories. 

  Here's an American Electric Lighting SP2 lamp. 

I have seen these along the Caltrans-maintained freeways all around San Diego County, presumably to make the viewing environment better for the Palomar Observatory located  on a mountain ridge in the northern part of the county.

[KEK Inc.]

I have seen these along the Caltrans-maintained freeways all around San Diego County, presumably to make the viewing environment better for the Palomar Observatory located  on a mountain ridge in the northern part of the county.

As I briefly mentioned in that post, I find it surprising that Santa Clara County doesn't follow suite. 

The more common ones I see in San Diego Country are extended versions of the Philips SRP

[StogieGuy7]

I hate to say it, but the old mercury vapor lights still do the best job!  Yes, I understand the various reasons for moving away from them, but I never liked the creepy pinkish hue of the high-pressure sodium lights.  Back in the late 70's and 1980's, people called them "crime lights" because (supposedly) they were first installed in high-crime areas.

About 5 years ago, we lived on a street that still had the old-fashioned incandescent bulbs.  They emitted a very pleasant, warm glow.  They're not particularly efficient, yet I grew fond of the light that they gave off.  I haven't seen the LED streetlights as yet, but it would be nice if the light they give off is visually more similar to cross between the Hg and incandescent bulbs.  The LED's certainly are efficient, a point that is very important these days. 

[DaBigE]

Unfortunately, LED streetlighting seems to require a bit more forethought than just simply swapping a lightbulb. There are two LED corridor installations near me that are a night and day difference from each other. One location was part of a complete road reconstruct...completely new streetlights and wiring. While these LEDs are very pleasing to the eye in terms of color, either the pole spacing or the LED unit type are all wrong (or both). There are more hot spots and unlit areas than with the previous HPS lighting.

The other location was a retrofit of existing HPS bulbs. No pole relocation was done along the entire corridor. In contrast to the other location, this corridor is, IMHO, lit perfectly. Not only is the color very true and pleasent, it is very, very even. There are no hot spots or dark areas; nothing but very evenly distributed lighting along the whole corridor.

It seems like the LED streetlights have a large learning curve. Not all LED units are created the same. When done properly, LED lighting can be a huge improvement. Local police tout that they feel they can get better perp descriptions due to the whiter light. Neighbors like them beause they can be aimed better and control light spill-off better (when properly spec'd/planned).

As for LED traffic lights, the smaller visors help marginally, if any at all, WRT snow build-up. Wisconsin has used the cut-off visors for as long as I can remember, and snow build-up isn't any less. Granted, the type of snow storm makes a huge difference. Wind-blown, wet snow is the worst, but ususally only effects lights facing one direction. We don't always get storms with that, so it isn't a problem with every snowfall that passes thru. When LED traffic lights were new, the problem of the lenses being covered was a hot topic, with virtually all news outlets having a story about them and the occassional crash that resulted from a driver assumming incorrectly. Below is a photo of the "high-tech" snow clearing tool they used.



With the blizzard that came thru last week, many signals were once again partially obscured, but there wasn't a peep made about them, nor have I seen any effort to clear them. Drivers have apparently learned to adapt.

[Mergingtraffic]

I like the pre-cursor to the copperheads, the round sphere like copper-heads used in the 60s and 70s at least around here in the Northeast.