In my last video we talked about the high pressure sodium lamp and its ubiquitous, use in outdoor lighting already, this type of lighting is starting to be phased out with various, technologies, with new LED technology among, the most common, now, given the robust nature of the sodium lamp and its proven track record in providing an efficient light source reliably, does, it make sense that we switched to newer light sources well. As usual in life there, are pros and cons so, let's start with a basic question why, do we use outdoor, lighting for, street lighting specifically. The basic answer is to improve safety particularly, pedestrian. Safety, the, odds of a crash of any kind are greater at night because it's harder to see with, the aid of artificial, roadway lighting a driver, can see much farther than their cars headlights shine especially, to the sides now, of course there are disadvantages, to large amounts of street lighting which we'll get to but, assuming safety, is the goal our sodium lamps good well, no, not, really remember, how I said that the sodium d-line is close to our eyes peak sensitivity but, only under photopic, daylight, conditions well. It turns out that our eyes see quite differently at night than during the day under. Night time schoo topic lighting conditions, our eyes actually see bluish light better and that, makes sense after all moonlight, and Starlight are pretty blueish so under these dimly lit conditions having, a greater sensitivity to, blue light would, mean we can see better, underscore. Topic lighting conditions, only the rod cells in our eyes are activated, rod, cells cannot distinguish, color but they are much more sensitive to light than the cone cells the, peak sensitivity of the rod cells is around 498. Nanometers, which, is a green blue color now. Of course under street lighting our cone cells are still active we can after all see colors and are not exclusively, using the rod cells this, dim but not quite dark lightning scenario, is often called mosaic vision, a mix, of the two still. Stimulation. To the rod cells will be far more visible and is more important, so, then how well does the light from sodium vapour lamps line up with our school topic light sensitivity, not, well this, is the CIE 1951. S go topic luminosity, function graph the, x-axis. Is the wavelength of light in nanometers and the y-axis is the eyes relative, sensitivity to these wavelengths under school topic nighttime conditions as you, can see peak sensitivity is around the 500 nanometer mark and where's, the wavelength produced by a sodium vapour discharge it's. About here 589. Nanometers the. Rod cells are barely activated, by a sodium discharge, while, the discharge may be extremely. Efficient at producing visible, light at night, time this light is fundamentally, misaligned with, our eyes sensitivity. See if you look at the response curves of schoo topic and photopic conditions, together you can see that the sodium discharge, lines up great with our photopic, vision but. When our eyes are adjusted, to nighttime lighting, conditions it's actually, pretty bad this, is why focusing, on the sodium d-line emissions seemingly perfect alignment with our vision is somewhat. Of a farce, while, it's true during the day it's, literally, quite far from the truth at night aside, from the simple spectral misalignment. Of the sodium lamp research, shows that people can indeed to see better under light sources with a bluer spectral, content in peter, moran tazed research for the lighting Research Center at the Rensselaer Polytechnic Institute, linked. Below survey, respondents, strongly, preferred the light from a 6,500, K correlated, color temperature, light source over that, of high-pressure sodium with, metrics of visibility, brightness, safety, and security color, rendering and overall, preference, all favoring, the newer light source which, also used only 55%, of the energy of the high-pressure sodium lamps it replaced the.
Study Which by the way is really comprehensive, and worth taking a look at was done in 2008, which was a tad before LED technology became, economically viable the. Study compared induction, lighting which is sort of like fluorescent lighting and worth a video on its own one day because it's pretty neat if not so practical any longer as well, as metal halide lighting to the sodium lamps for the purpose of creating a recommendation to a local utility, company, the. Conclusion, was that metal halide didn't make sense due to higher maintenance costs, but, induction, would make tons of sense but, I also liked this final recommendation, white. Light emitting diodes should be considered as replacements, for HPS street lighting in about three years time when, their efficacy is higher and their cost has reached reasonable, levels to be economically, viable growing. Utilities, may want to consider postponing decisions. On street light replacements, until, white LEDs become economically, available well, it's been about ten years since that study and LEDs, are economically. Viable in fact, they've become in, right oblique anomic, Lee viable but, before we move on to them let's go over the main issue once more because. Of the spectral, misalignment. Of the sodium vapour lamp with our school topic and Mesaba Clyde sensitivity, it takes, more light output, from a sodium lamp to produce the same visible, light level from, a bluer light source, in fact dr. Alan Lewis of the New England College of Optometry measured. Individual's, response time to a hazard approaching from the sides and found, that in well-lit areas such as a major motorway, a high-pressure sodium light system needs to produce 3.9, times as much light as a metal, halide source, to achieve the same response time the. Effect is even greater in dimly lit areas where, he found that 7.8. Times as much light from high-pressure sodium was required to match response, time under cooler metal, halide light sources so it seems as though the high-pressure sodium light is less efficient, than it appears on paper and that roadways safety is greatly increased when light sources are used that are tuned to our schoo topic and mazovick light sensitivity, it's. Looking pretty bad for high pressure sodium but. There's one thing that HPS, technology, doesn't do that bluer light sources might that, my friends is circadian rhythm, disruption, research. Has suggested that the color of light we are exposed, to has a great impact on what time our biological clocks, think it is the. Shorter wavelength of daylight Sun and blue sky may, help keep us awake by suppressing melatonin production, and, the long wavelength, light of the sunset may, signal our bodies to sleep by allowing melatonin, to seep into our blood streams to. Help us understand, the impact different light sources can have on circadian rhythm disruption light. Sources are characterized, by their melon optic content, there's, a great source from the US Department of Energy linked down below which goes over this in much greater detail, but as a general overview with, high pressure sodium technology, normalized, at one for both schoo topic light content, and Mellon optic light content a metal, halide lamp with a color temperature of about 4,000, K will, have about 2.5, to 2.8, times as much schoo topic light content, but, also produces, 3.16. 23.7. Five times as much melon topic light content, if, you look at the various color temperatures, of LED light sources you, can see that as the color temperature increases, both, schoo topic light content, and melon, Opik light content, increase however.
Melon, Topic light content increases at a greater rate than schoo topic light what this means is there's a trade-off and it's, complicated. The, higher the color temperature the more scotopic, light it produces which means you could use less light and thus less energy so you get the same perceived brightness and safety levels but, because. Melon Opik light content, increases at a greater rate although, you may need less light of, a higher color temperature, it will disrupt circadian, rhythm, to a greater extent you. Can see that high-pressure sodium has among the lowest melon, Opik light content, of any light source with, only amber leds and low pressure sodium producing. Less melon Opik light so, then we're presented, with a choice we. Can clearly use less energy and expect, a safer, nighttime driving experience, with light sources of higher color temperatures, but. This may cause unwanted, side effects that sodium lighting largely, doesn't and this, is completely, ignoring aesthetic, preferences, I myself, generally. Detest, cooler lighting as I find it hard and unpleasant but I can't acknowledge its safety advantages, in my area, and interstate, 88 many, of the roadway lights have been changed, from high pressure sodium to LED the. Change is dramatic with, visibility greatly. Enhanced, once under the cooler light as much. As I don't like the color I can tell that it's a lot safer, visibility. In my periphery is tremendously, better and I'm certain, these new lights are using less energy than those they replaced before I move into the conclusion of this video let's discuss the issue of light pollution light. Pollution is exactly what it sounds like excess. Light in our environment, that is irritating, unnecessary, poorly, distributed or in general unwanted. Outdoor. Lighting is by far the most prolific, source of light pollution and it has gotten so bad that people living anywhere near a city can barely, see the night sky, there's, even an anecdote, about a widespread blackout, in Los Angeles causing, many panicked, 911. Lifelong. Residents, who had never seen the Milky Way before and were a little scared of it light pollution is a complicated, problem but the LED may actually help to solve it now, to be clear the solutions I'm about to offer aren't exclusive, to LEDs but the way light is emitted from an LED chip makes, controlling it relatively, easy, so, first let's discuss one of the biggest causes of light pollution lights. That point up this. Is less obvious than it seems but it's in important, right, outside my apartment are, dropped lens Cobra luminaires containing, high-pressure sodium lights because. The lens protrudes, downward. From the fixture a lot, of light escapes to the sides and indeed upwards, I'm, on the fourth floor of my building and my eye level is above these street lights but, I can still see the source of the light this. Is not ideal for a number of reasons first, a lot of light is being wasted by lighting up things that are not, the road that's, kind of dumb but secondly.
A Lot of this light is going up into the sky granted. This style of fixture isn't the worst offender, but a better design would be a flat lens that does not allow light to escape above, the horizontal. This. May still throw light farther to the sides than necessary, but, none of it will end up lighting the sky the. Worst offenders, for this kind of light pollution are lights that illuminate buildings. By shining upwards, wall, pack lights without shielding, and these, decorative, fixtures, I'll admit they're pretty but, they're really wasteful, recently. I was on an airplane flying, into Chicago, at night I took some videos as we landed, and you can see the difference between a well-managed, light and a poorly managed light this, roadway is lit well I cannot, see the actual light sources I can only see the reflected, light from the road that's. What we want as we, got closer to the airport these, neighborhoods, had tons, of lights that were visible from above much. Of the light produced by these lamps is shining into the sky and being wasted, I should. Not be able to see the actual light source from an airplane yet. I can this. Is contributing, to sky glow sky, glow is what makes the night sky hard to see when you're close to a city this, is probably the most widespread light, pollution problem, and while it's not caused exclusively. By poorly designed fixtures, they, are a major component but. Once again the, solutions, the sky glow are complicated. Largely. Because light sources that cause the least amount of sky glow are, high and low pressure sodium in fact. Low pressure sodium is used widely around large astronomical, observatories, because they're nearly monochromatic, light, output can easily be filtered out eliminating. Any sky glow they create I saw. A large number of people saying that high-pressure sodium can also be filtered out but, I don't think that's true due to the pressure broadening and their spiky or output, someone. Correct me if I'm wrong but I could only find references, to low pressure sodium being used around observatories. Anyway. Where it gets tricky is that an LED light source has about three times as much sky glow impact, than a high-pressure sodium light but. Also you need less of it so perhaps the sky glow impact is similar, in, addition, the sky glow impact of incandescent lighting is barely higher than low pressure sodium so. It could be that led street lighting correlated, to a 2700. K color temperature, causes less sky glow than high-pressure sodium but. I think further research needs to be done there in any case what makes LEDs potentially, much better at reducing sky, glow is the optical, systems that can be combined with them early. LED fixtures may have used a large number of small 1 watt LEDs, and tiny, lenses to direct their light some. Really bad designs may have simply had an exposed, chip providing, little directional, control you, still see this a lot in cheap floodlight fixtures, but, newer fixtures, like these from Cree will use large chip onboard admit errs like these 10 watt chips but larger and because, they only emit light in one direction it's very easy to control their output with a lens you can see on the spec sheet that there are five lenses in total the larger fixtures have more most. Importantly, the optic system is customizable, depending. On fixture height and spacing you may need a wider spread of light or a shorter one due. To the customizable. Optics you can get wonderfully, consistent, lighting on a road surface such as this area here this, may also help prevent light pollution because, less overall light is needed the, hot spots of Lights you see from above here I mean some areas get too much light and others get too little a Morse, code Opik light source with better and more consistent control, may, not only reduce light pollution but. May use less energy and provides safer driving now many of these developments, are rather new especially the newer optic designs but, the advantages, of LED lighting become confused, when drop-in, replacement, bulbs are used I don't, have any major issues about going this route after, all replacing, the entire fixture, can be costly and some, drop-in designs are fairly good but, the optic, system of a sodium mercury, vapor or metal halide fixture, is designed, to reflect and project light emanating, from a tiny arc tube which, an LED drop-in can't recreate. Many of the complaints regarding poor light distribution and LED replacement lamps may simply be from the use of these replacements. Then. There's the issue with existing ballasts. Some, drop in lamps claim to work with existing ballasts, but I have a few misgivings, regarding how, well their power supplies deal with the voltage the ballast provides, particularly.
If The high voltage igniter sends, some crazy voltage, spikes to the LED dropping I'm, sure they can be designed to cope but, it still worries me someone so then we have a series of complicated, choices to make Soniya, vapor lights are pretty efficient have only a moderate contribution, to sky glow caused, only minor circadian. Rhythm disruption if any and have a proven track record of reliability, but. Their color also makes them far less effective. At improving safety, and due, to the misalignment, of their output with our scope topic light sensitivity, they require more light and thus use a lot more energy than a wider light source perhaps. Less an issue but still important is that they contain both mercury. And elemental, sodium meaning. Their disposal, is far more dangerous and complicated if we were to switch to a white LED source with a color temperature of about 5,000, K nighttime. Visibility would, be greatly increased, studies. Have shown that people see hazards, far sooner under this light and as the bluer wavelengths, match our schoo topic and mess up at color sensitivity more closely we, can use less of it while also achieving a greater safety benefit this, reduces, the need for energy, however. This bluer light contributes, more to circadian, rhythm disruption and, sky glow but some of that is mitigated, by the lower output required, by these light sources still. Many, people may not find the aesthetics, of this light source pleasing, one. Possible, compromise would be to use a warmer, color temperature, LED light source data. From the US Department of Energy tells us that a 3000, K LED, light would produce 1.89, to two point three nine times as much go topic light as a high pressure sodium lamp while increasing, Mellon optic content between two point one and two point nine nine times, because. Of its greatest go topic output a 3,000, K LED replacement should, only need to produce about half as much light as a high-pressure sodium lamp this. Effectively, cuts the circadian rhythm disruption potential. In half to placing. It near about the same as high-pressure sodium the, greatest downside, to using a warm color temperature, LED is in their efficiency, the, efficiency of. These lights is very similar to that of an average high pressure sodium lamp at 67. Lumens per watt these 3000, K LEDs are just slightly less efficient, than the sodium lamp featured in my last video although. You would need only about half as much light output, there are high pressure sodium lamps, which approach 150. Lumens per watt this. Would mean that a 3000, K LED will use just about as much energy as a very, efficient, high pressure sodium lamp I'd, still call that good but it makes replacement, less compelling, to. Normalize the effects of scotopic light content, I've multiplied, the lumens per watt number by this Co topic light content, for the following light sources as you, can see the normalized, efficiency, of the LED goes up considerably as the color temperature does due, to both luminous, efficiency and greater scotopic content, this, is likely why most LED street lamp installations, are done with the bluish 50 700 K and higher color temperatures, you. Can use the least amount of energy to produce the same amount of perceived brightness and safety, however. The normalized, efficiency, of even the 3000, k LED is very similar to that of high-pressure sodium and few, HPS lamps actually output 150. Lumens per watt also. The calculated, lumens per watt of the LED is based on the input power of the fixture so, the losses in the ballast which are fairly high for high pressure sodium aren't, accounted for here to conclude although the high pressure sodium light is very efficient, its primary, output color is misaligned, with our nighttime visibility only. About a quarter of its light is actually effective, at stimulating the, cells in our eyes although. The cool color temperature, 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 sky glow using these bluer light sources, still. It seems clear that the high pressure sodium lamp 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 meeting the efficiency, of high pressure sodium when, schoo topic 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, 5700. K lighting either. Way it seems clear that LED technology will, very soon overtake, the tried-and-true high pressure sodium lamp just, as the HP s lamp itself replaced, the mercury vapour lamp and in, 40 or 50 years who, knows what technology, might light our roadways. So. I have a couple of things to close out first you may have noticed in my chart that the mercury vapor lamp had a normalized efficiency, of over 100 lumens per watt and the, 50 watt sodium lamp in the last video was only 78 lumens, per watt mercury. Vapor bulbs do have considerable, operating, disadvantages, compared to high pressure sodium most, notably their steady decrease in light output as they age but, I think it is somewhat humorous that our current understanding of, the visual system suggests. That sodium light may have been a step backwards, in some situations, 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 you. Can clearly see in this chart that there is blue light content, and nearly all light sources and lower, color temperature, LEDs have less blue light content, than their higher color temperature, varieties, I don't. Doubt that blue light can disrupt circadian rhythm that much seems certain 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, that it can be tuned in pretty much any way you'd like I also want to give a shout-out to V Westlife for the suggestion, of LED fixtures with both high and low color temperatures, that, will switch to the warm light later in the night I think, that's a great idea though. Obviously it would add expense to any fixture however. I was surprised to learn that the cree LED fixtures, i've been using as a reference are, all capable of dimming and they have a 0 to 10 volt control input to enable this reducing. Light levels to perhaps 50% of normal after midnight might become a common practice and i think that would be pretty wise maybe. This will get combined with technology similar to Philips warm glow and we'll get incandescent, like lightning at night for, those worried about light pollution for astronomical observatories. There are amber, LED streetlights available designed to replace low pressure sodium lights this, is also great news for wildlife many, animals cannot see the wavelength of light produced by low pressure sodium so, this light source is used where lights may be disruptive, one, particular, example is near beaches where sea turtles lay their eggs after. They hatch baby sea turtles follow moonlight, to the ocean and street, lighting was confusing, the poor things and they were travelling inland since. They cannot see the wavelength of a low pressure sodium light or its amber LED equivalent, they, aren't confused and successfully. Make it to the ocean where they belong as a last little tidbit the spec sheet from Cree says that their LED cobrahead replacements, should produce at least 95, percent of, their original light output, after a hundred, thousand, hours assuming. The driver and heatsink are robust enough these fixtures should last well beyond twenty years that. Is impressive, thanks, for watching I hope you enjoyed the video if you haven't subscribed, to technology, connections, yet and you like my nerdy deep dives into whatever floats through my head what, are you waiting for hit the button please, as. Always thanks, to everyone who supports this channel on patreon, you are all making a big difference and it's super awesome of you if you're, thinking of joining these awesome people and becoming a patron yourself why, not check out my patreon page thanks. For your consideration and I'll see you next time.
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2018-06-20