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The LED's Challenge to High Pressure Sodium

Technology Connections · Youtube · 6 HN comments
HN Theater has aggregated all Hacker News stories and comments that mention Technology Connections's video "The LED's Challenge to High Pressure Sodium".
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Now that we know why street lights are orange, let’s look at whether or not they should still be so. The answer isn’t as straightforward as it might seem. Although newer technology seems to surpass HPS in nearly all respects, there are still considerations to be made.

Link to the Previous Video:
https://youtu.be/U1dMlVwUsrA

Technology Connections on Twitter:
https://twitter.com/TechConnectify

Sources (lot’s of great ones!):
Lighting Research Center study comparing induction and metal halide sources to HPS:
http://www.lrc.rpi.edu/researchAreas/pdf/GrotonFinalReport.pdf

US Department of Energy’s information on blue light sources in street lighting:
https://www.energy.gov/sites/prod/files/2017/03/f34/Street%20Lighting%20and%20Blue%20Light%20FAQs.pdf

University of Pittsburgh’s environmental assessment of LEDs (in case you are worried about the extra e-waste compared to the mercury and sodium):
https://www.sciencedaily.com/releases/2010/03/100308132136.htm

Some general info on spectral sensitivity of the human eye:
https://light-measurement.com/spectral-sensitivity-of-eye/

Basic info on light pollution (including relative impacts on sky glow) came from everyone’s favorite reliable source of knowledge:
https://en.wikipedia.org/wiki/Light_pollution

Spec sheet for the Cree LED
http://api.icentera.com/v2/getfile.aspx?f=E9CE983DDF2101638FA38D240926FE55E07EDD8D97F195ABD14AC9FFAF3CAF03C2995E6AD9E245B0

Product overview:
http://lighting.cree.com/products/outdoor/street-and-roadway/xsp-series

More info on spectral misalignment:
http://www.patmullins.com/sodiumpollution.html

Where Dr. Alan Lewis’ research is cited:
http://www.thelindy.com/uploads/Should_vision_influence_roadway_lighting_design.pdf


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Hacker News Stories and Comments

All the comments and stories posted to Hacker News that reference this video.
You might be interested in this video https://www.youtube.com/watch?v=wIC-iGDTU40.
I'm reminded of a Technology Connections video about what happened when his town switched from incandescent to LED stop lights <https://www.youtube.com/watch?v=GiYO1TObNz8>

Of course, while I was looking that up I found out he made a video about sodium vapour lights! <https://www.youtube.com/watch?v=wIC-iGDTU40>

Here's a quite good video about the pros and cons of LED vs high/low-pressure sodium street lamps: https://youtube.com/watch?v=wIC-iGDTU40 . It goes into lamp efficiency, how our eyes see differently at night, response time under different sorts of light, color temperature, circadian rhythm disruption, and light pollution.
teslabox
It's a good video, but it's also a case study in being 'almost right'. The almost-correct interpretations cascade and result in a faulty conclusion: that blue-white LED streetlights are better than orange-white streetlights. Various comments object to the faulty conclusion ([1], for example).

At the end he at least addresses his ignorance:

> [18:39] You may have noticed that I didn't talk about the blue light from LEDs, and how this is supposedly ruining our eyes. That's because the "science" behind this is questionable, at best.

> [18:55] [discussion of chart with percentage blue light of various light sources]

> [19:04] [...] but considering that our eyes can withstand the intensity of sunlight, which is far far greater than any normal artificial light source, and also has a lot of blue light, and ultraviolet, which definitely is harmful, I think the 'blue light' thing is just fear-mongering. If someone can point to some verified, peer-reviewed research supporting this, and not a dodgy website, I'll consider changing my stance. In any case, the high flexibility of LED technology means it can be tuned in pretty much any way we like.

The research on the harm of blue light is out there -- For example, one of the comments links to "Effects of blue light on the circadian system and eye physiology" [0]. (only partially read at this point - I don't know if this paper gets into the mechanism of damage done by blue light, as I understand it...)

The sun hangs high in the sky and casts light on everything. We never need to look at the sun directly, we use the sun's light indirectly, after it bounces off of things. The atmosphere scatters the sun's blue light before it gets to us [2]. Artificial lights hanging on poles emitting photons we can't avoid having beamed directly into our eyes... Blue photons have relatively higher energy levels, and different physiological effects, than orange photons... [note to self: expand on this.]

The preceding video was about High Pressure Sodium lights, which I thought was good too: https://www.youtube.com/watch?v=U1dMlVwUsrA

My transcription of the video's faulty conclusion (italics added):

> To conclude: although the High Pressure Sodium light is very efficient, its primary output color is misaligned with our nighttime visibility. Only about 1/4 of its light is actually effective at stimulating the cells in our eyes. Although the cool color temperatures of many LED replacements is harsh and aesthetically displeasing, studies have shown that it is not only more efficient, but also makes driving at night safer. There is, however, the potential for greater circadian rhythm disruption and larger amounts of skyglow, using these bluer light sources.

> Still, it seems clear that the High Pressure Sodium is on its way out. Advancements in LED technology are happening at a breakneck pace. Just 10 years ago, they weren't seen as viable, but today even the least efficient of LED replacements ends up emitting the efficiency of High Pressure Sodium once scotopic light output is considered.

> As it stands in 2018, we are faced with the choice of efficiency over aesthetics. I'm pretty sure I'd enjoy roadways lit with relatively-warm 3000K LEDS, and these also wouldn't disrupt sleep much. But you can save a lot more energy, and potentially have safer roadways, with 5700K lighting.

> Either way, it seems clear that LED technology will very soon overtake the tried-and-true High Pressure Sodium lamp, just as the High Pressure Sodium itself replaced the mercury-vapor lamp. And in 40 or 50 years, who knows what technology might light our roadways.

[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4734149/pdf/mv-... - "The radically different power spectrums can look similar when viewed directly by the eye, irrespective of how much blue emission is present."

[1] https://www.youtube.com/watch?v=wIC-iGDTU40&lc=Ugx6MYdsMY6I_...

[2] https://en.wikipedia.org/wiki/Rayleigh_scattering#Cause_of_t...

edit: this page has a discussion of drop-sag lights vs. proper fully-shielded lights: http://www.skykeepers.org/good-bad-lights-cv.html

kibwen
Thanks, I appreciate the thorough follow-up. :)
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.

Relevant Technology Connections video: https://www.youtube.com/watch?v=wIC-iGDTU40

Zak
Warm white LEDs put out a broad spectrum. That's a feature for most illumination use cases, but it's hard to filter out of a telescope.
jacobolus
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?)

The youtube channel Technology Connections has a couple of interesting articles about LED (and sodium-vapor lamp) bulbs in street lighting: https://www.youtube.com/watch?v=wIC-iGDTU40

(Actually, most if his videos are pretty interesting to explore, especially the ones about early TV)

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