WEBVTT Kind: captions Language: en 00:00:00.130 --> 00:00:04.440 In many parts of the world, if you’re taking a stroll outside or driving your car around 00:00:04.440 --> 00:00:08.670 at night time, you’re likely to be basked in the orange-peach-gold-yellow whatever you 00:00:08.670 --> 00:00:11.790 want to call it glow common in street lighting. 00:00:11.790 --> 00:00:16.360 This particular hue of light has been a staple of outdoor lighting for decades, and it continues 00:00:16.360 --> 00:00:17.619 to be used widely. 00:00:17.619 --> 00:00:19.400 But, why that color? 00:00:19.400 --> 00:00:21.820 Well, it’s special kind of light bulb. 00:00:21.820 --> 00:00:23.919 Thanks for watching, I hope you enjoyed the video. 00:00:23.919 --> 00:00:26.460 No, of course we’re gonna go into more detail than that! 00:00:26.460 --> 00:00:30.029 Much of the world’s street lighting (and indeed more broadly outdoor lighting) uses 00:00:30.029 --> 00:00:32.500 sodium vapor lamp technology. 00:00:32.500 --> 00:00:35.040 The most common is high pressure sodium. 00:00:35.040 --> 00:00:39.050 This artificial lighting technology is a type of discharge lamp. 00:00:39.050 --> 00:00:44.140 Discharge lamps are very common in many applications because they are a very efficient way of creating 00:00:44.140 --> 00:00:45.920 light from electricity. 00:00:45.920 --> 00:00:49.720 Among the earliest sources of artificial light is the incandescent light bulb. 00:00:49.720 --> 00:00:54.470 Many, many people were working on its invention, so to say one person invented it is disingenuous 00:00:54.470 --> 00:00:59.120 at best, so I’m just not gonna say anything because, well, no matter what I say I’ll 00:00:59.120 --> 00:01:00.120 be wrong. 00:01:00.120 --> 00:01:01.989 But its principle of operation is really simple. 00:01:01.989 --> 00:01:03.180 Hot things glow. 00:01:03.180 --> 00:01:04.370 Make thing hot. 00:01:04.370 --> 00:01:06.130 Make thing hot without burning. 00:01:06.130 --> 00:01:07.549 Put hot thing in vacuum. 00:01:07.549 --> 00:01:09.409 Now that thing can’t burn away. 00:01:09.409 --> 00:01:10.409 Light! 00:01:10.409 --> 00:01:14.090 By running electric current through a thin wire, that wire will get hot because of resistance 00:01:14.090 --> 00:01:15.740 and it will glow. 00:01:15.740 --> 00:01:16.790 Tada! 00:01:16.790 --> 00:01:20.539 The earliest light bulbs used a carbon filament, but shortly thereafter improvements in the 00:01:20.539 --> 00:01:24.819 ability to make tungsten filaments allowed for a brighter and longer-lasting bulb due 00:01:24.819 --> 00:01:27.170 to tungsten’s much higher melting point. 00:01:27.170 --> 00:01:31.329 I must recommend this video by the Engineer Guy about the tungsten filament lamp. 00:01:31.329 --> 00:01:32.329 It’s great. 00:01:32.329 --> 00:01:33.579 I’ve put a link down below. 00:01:33.579 --> 00:01:36.539 But anyway, incandescent lights aren’t very efficient. 00:01:36.539 --> 00:01:40.049 Creating light through incandescence wastes the vast majority of electrical energy on 00:01:40.049 --> 00:01:44.439 radiation that isn’t visible light--simply infrared light and heat. 00:01:44.439 --> 00:01:48.840 Among the most common ways to measure efficiency is in lumens per watt, and incandescent bulbs 00:01:48.840 --> 00:01:51.799 are typically around 10 lumens per watt. 00:01:51.799 --> 00:01:56.209 Really efficient halogens and high-powered incandescents can reach 20 lumens per watt, 00:01:56.209 --> 00:01:57.209 but it’s still not great. 00:01:57.209 --> 00:02:00.460 But a discharge lamp, well that can be very efficient. 00:02:00.460 --> 00:02:05.420 When you send an electric discharge--basically a small electric arc--through an ionized gas, 00:02:05.420 --> 00:02:06.420 you get light! 00:02:06.420 --> 00:02:09.700 I wasn’t very good at Chemistry in high school, so I’m just gonna read the passage 00:02:09.700 --> 00:02:11.780 from Wikipedia which explains why. 00:02:11.780 --> 00:02:12.780 Ehem. 00:02:54.060 --> 00:02:57.870 In layman’s terms, if you create an arc discharge through some gases, then because 00:02:57.870 --> 00:03:01.190 of ions and stuff bouncing around, you’ll end up with photons and depending on what 00:03:01.190 --> 00:03:05.680 the gas is, these photons will be a specific frequency and thus will produce a specific 00:03:05.680 --> 00:03:06.730 color of light. 00:03:06.730 --> 00:03:10.180 I’ve put a link to the Wikipedia article down below because it has some great images 00:03:10.180 --> 00:03:12.530 of the colors produced by specific gases. 00:03:12.530 --> 00:03:16.030 The most common type of discharge lamp is actually the fluorescent lamp. 00:03:16.030 --> 00:03:19.810 The glass tubes in fluorescent lamps are filled with an extremely low pressure gas mixture 00:03:19.810 --> 00:03:24.940 made mostly of argon or neon used as a starter gas, and a wee bit of mercury which produces 00:03:24.940 --> 00:03:26.680 the main discharge. 00:03:26.680 --> 00:03:32.590 Mercury vapor on its own produces a very cyanish blue light, but it also produces a TON of 00:03:32.590 --> 00:03:37.430 ultraviolet light, which the phosphors that coat the glass will convert into visible light, 00:03:37.430 --> 00:03:41.900 and depending on the phosphors used you can get a very pleasant or very ghastly white 00:03:41.900 --> 00:03:44.370 light of various color temperatures. 00:03:44.370 --> 00:03:48.140 You can even use colored phosphors to make any color of light you want. 00:03:48.140 --> 00:03:51.760 Sodium vapor lamps rather than using mercury use...sodium. 00:03:51.760 --> 00:03:52.760 You guessed it! 00:03:52.760 --> 00:03:56.870 When sodium is ionized, its discharge is a very distinctive yellow hue with a wavelength 00:03:56.870 --> 00:03:59.330 of 589 nanometers. 00:03:59.330 --> 00:04:03.480 Low pressure sodium lamps emit light of pretty much just that wavelength. 00:04:03.480 --> 00:04:07.880 While useful, and actually the most efficient discharge lamp available, this light is monochromatic 00:04:07.880 --> 00:04:11.940 with a color rendering index of zero, so it is only useful as street lighting, and even 00:04:11.940 --> 00:04:13.710 then it's not great. 00:04:13.710 --> 00:04:17.830 Low pressure sodium lights are going to appear on this channel in the not-too distant future, 00:04:17.830 --> 00:04:21.610 but for now we’re sticking with high pressure sodium which is far more common these days. 00:04:21.610 --> 00:04:24.550 This is a 50 watt high pressure sodium lamp. 00:04:24.550 --> 00:04:29.500 This is the second smallest common size, with 35 watts occupying the smallest spot, but 00:04:29.500 --> 00:04:32.110 they go all the way up to 1,000 watts. 00:04:32.110 --> 00:04:36.130 In the center of the bulb is a small tube made of aluminum oxide--which for those that 00:04:36.130 --> 00:04:37.870 don’t know is what rubies are. 00:04:37.870 --> 00:04:42.090 Of course this is synthetic, but due to the crazy reactivity of elemental sodium, it needs 00:04:42.090 --> 00:04:46.450 to be contained in something that will A) contain it without reacting with it and B) 00:04:46.450 --> 00:04:49.940 is quite strong and can withstand a lot of heat. 00:04:49.940 --> 00:04:52.220 Aluminum oxide fits the bill perfectly. 00:04:52.220 --> 00:04:56.280 Inside the tube there’s a bit of xenon, as well as an amalgam of mercury and sodium. 00:04:56.280 --> 00:04:59.880 The mercury is added in high pressure sodium lamps to control the rate at which the sodium 00:04:59.880 --> 00:05:00.880 vaporizes. 00:05:00.880 --> 00:05:04.520 It also helps to improve the color rendering of the lamps by adding some blue light to 00:05:04.520 --> 00:05:05.620 their output. 00:05:05.620 --> 00:05:10.560 Just like any discharge lamp, a ballast is needed to limit the current the bulb can consume. 00:05:10.560 --> 00:05:15.660 Due to an arc discharge having negative resistance, as current goes up, resistance goes down, 00:05:15.660 --> 00:05:19.930 and power consumed will just skyrocket without a ballast or choke to stop it from destroying 00:05:19.930 --> 00:05:20.930 itself. 00:05:20.930 --> 00:05:23.770 The ballast will have either two or three components. 00:05:23.770 --> 00:05:27.470 First is the actual ballast itself which is similar in construction to a transformer, 00:05:27.470 --> 00:05:31.520 then there is the ignitor which is needed to start the lamp, and some ballasts including 00:05:31.520 --> 00:05:36.680 this one will place a large capacitor across the leads to help correct the poor power factor 00:05:36.680 --> 00:05:39.520 brought about by the inductive nature of the ballast. 00:05:39.520 --> 00:05:43.460 As with many discharge lamps, high pressure sodium lamps generally go through a distinct 00:05:43.460 --> 00:05:44.930 warmup routine. 00:05:44.930 --> 00:05:48.170 When first powered on, the ignitor is working to strike the arc. 00:05:48.170 --> 00:05:52.870 Once it’s been struck, it briefly glows a pinky-blue color as the xenon is ionized. 00:05:52.870 --> 00:05:56.260 Quickly the mercury starts to vaporize, and as it does so the ionization of the mercury 00:05:56.260 --> 00:06:00.430 vapor releases a pale blue color, often appearing as grey. 00:06:00.430 --> 00:06:03.970 But then the distinctive yellow of the sodium discharge takes over. 00:06:03.970 --> 00:06:10.150 As the sodium vaporizes, the lamp emits a very pure yellow color, which is not at all white. 00:06:10.150 --> 00:06:13.040 This is what the light from low pressure sodium lamps looks like. 00:06:13.040 --> 00:06:16.730 But then the high pressure in high pressure sodium does its thing. 00:06:16.730 --> 00:06:20.710 The arc tube is very small, and the gases inside it become quite hot. 00:06:20.710 --> 00:06:24.930 In a space of given volume, with increased temperature comes increased pressure. 00:06:24.930 --> 00:06:29.590 This results in a phenomenon called pressure broadening, which causes ordinarily weak spectral 00:06:29.590 --> 00:06:34.460 emissions to become stronger, and thus the lamp emits more wavelengths of light. 00:06:34.460 --> 00:06:38.570 Once completely warmed up, the pressure broadening causes the light to appear less yellow and 00:06:38.570 --> 00:06:42.440 more white, though still with a prominent yellow cast. 00:06:42.440 --> 00:06:46.850 Color perception is subjective, but I’d call this a orangey-peachy-gold color with 00:06:46.850 --> 00:06:48.080 a hint of pink. 00:06:48.080 --> 00:06:49.080 You are… you, 00:06:49.080 --> 00:06:49.980 yes? 00:06:50.680 --> 00:06:51.720 You are warming up right, 00:06:51.720 --> 00:06:53.060 you’re on? 00:06:57.560 --> 00:06:58.560 OK Good. 00:06:58.570 --> 00:07:01.750 This is the most exciting part of the video, I guarantee it. 00:07:01.750 --> 00:07:05.000 I bet you’ve never had a video more exciting than this one. 00:07:06.220 --> 00:07:08.699 I don’t even know what this looks like on camera. 00:07:08.699 --> 00:07:10.070 So we’ll, we’ll just. 00:07:10.070 --> 00:07:11.670 I should--I should have looked into that! 00:07:11.670 --> 00:07:12.670 Yeah. 00:07:12.670 --> 00:07:13.860 That was good. 00:07:13.860 --> 00:07:18.060 This light is extremely efficient, and the output it makes with only 50 watts is pretty striking, 00:07:18.060 --> 00:07:19.750 just like its arc. 00:07:19.750 --> 00:07:20.750 Ha! 00:07:20.750 --> 00:07:25.150 If I put it side-by-side with a 100 watt equivalent LED bulb (in a lamp that would never, EVER 00:07:25.150 --> 00:07:29.430 have an HPS bulb in any ordinary setting), you can tell that it’s much brighter. 00:07:29.430 --> 00:07:33.570 For half the energy of its incandescent equivalent, it’s producing about triple the light, going 00:07:33.570 --> 00:07:34.830 off lumens. 00:07:34.830 --> 00:07:39.889 This particular lamp produces 78 lumens per watt, which is 4 to 8 times greater than an 00:07:39.889 --> 00:07:40.889 incandescent. 00:07:40.889 --> 00:07:43.940 Some high pressure sodiums lamps are nearly twice as efficient as this one, producing 00:07:43.940 --> 00:07:45.790 150 lumens per watt. 00:07:45.790 --> 00:07:50.090 Also, and this is hard to demonstrate on video, but the light from the sodium lamp appears 00:07:50.090 --> 00:07:52.960 to travel farther than that of the “incandescent”. 00:07:52.960 --> 00:07:56.520 The walls on the opposite side of the room seem much, much brighter than they do with 00:07:56.520 --> 00:07:58.479 a standard white light. 00:07:58.479 --> 00:08:02.500 Some of that has to do with the sodium D-line, that’s the main yellow spectral emission, 00:08:02.500 --> 00:08:06.100 closely matching the peak sensitivity of the cells in our eyes. 00:08:06.100 --> 00:08:09.020 But only under photopic, daylight conditions. 00:08:09.020 --> 00:08:13.290 This gets kinda complicated and we’ll get into it, but the peak sensitivity of the average 00:08:13.290 --> 00:08:20.210 human eye is 555 nanometers, and the HPS lamp’s peak output of 589 isn’t far off. 00:08:20.210 --> 00:08:26.310 But don’t fixate on that too much because, spoiler alert, this turns out to be a bad thing. 00:08:26.310 --> 00:08:29.800 Before we move on to their advantages, let’s quickly discuss why we don’t use this light 00:08:29.800 --> 00:08:32.360 source for general household illumination. 00:08:32.360 --> 00:08:36.080 Every artificial light source has what’s called a CRI, or color rendering index. 00:08:36.080 --> 00:08:42.310 A CRI of 0 means it’s impossible to distinguish color, and a CRI of 100 is a perfect score, 00:08:42.310 --> 00:08:43.980 which the sun has. 00:08:43.980 --> 00:08:49.200 Incandescent lights has a CRI of 99, but most other light sources aren’t so high. 00:08:49.210 --> 00:08:53.430 Poor CRI plagued many fluorescent light sources, particularly early ones. 00:08:53.430 --> 00:08:57.640 Though the light of a CFL might appear perfectly white, the colors of objects underneath it 00:08:57.640 --> 00:08:59.240 might seem a little off. 00:08:59.240 --> 00:09:05.200 A cheap CFL might have a CRI as bad as 70, which will be generally OK but which can cause 00:09:05.200 --> 00:09:07.600 some colors to appear oddly. 00:09:07.600 --> 00:09:12.750 The average high pressure sodium lamps has a color rendering index of about, drumroll please. 00:09:12.750 --> 00:09:13.780 21. 00:09:14.320 --> 00:09:15.380 It’s pretty bad. 00:09:15.390 --> 00:09:18.839 Here’s an assortment of colorful objects as lit by normal white light. 00:09:18.839 --> 00:09:22.130 And now, observe how they look under high pressure sodium. 00:09:22.130 --> 00:09:25.390 I’ll show them as it warms up, because it demonstrates how when the sodium emission 00:09:25.390 --> 00:09:28.470 first comes into play, it is almost monochromatic. 00:09:28.470 --> 00:09:31.710 See how you can barely tell what color things are supposed to be? 00:09:31.710 --> 00:09:37.160 As the pressure broadening occurs, you can start to see color, but it is still just odd. 00:09:37.160 --> 00:09:40.750 The strangest-looking object I discovered was this can of La Croix. 00:09:40.750 --> 00:09:42.500 Take a look at this side by side. 00:09:42.500 --> 00:09:47.860 The sodium light mutes all of the color differencesin the background, and the text becomes bizzare looking. 00:09:47.860 --> 00:09:50.080 Food in general looks… 00:09:50.080 --> 00:09:52.649 unappetizing under high pressure sodium lighting. 00:09:52.649 --> 00:09:53.970 Pasta and red sauce? 00:09:53.970 --> 00:09:56.920 The sauce will look more of a pukey-brown. 00:09:56.920 --> 00:09:58.310 Having some yellow tortilla chips? 00:09:58.310 --> 00:10:00.529 Yeah they’re more of a chartreuse now. 00:10:00.529 --> 00:10:03.871 Of course, their slow warm up time would be inconvenient for home use, so they’re really 00:10:03.871 --> 00:10:07.570 suited for general illumination where they’ll run all night. 00:10:07.570 --> 00:10:11.610 So, street lights, parking lots, security lighting, and other dusk-to-dawn applications 00:10:11.610 --> 00:10:13.830 are where these lamps really shine. 00:10:13.830 --> 00:10:16.370 I came up with that all on my own. 00:10:16.370 --> 00:10:18.350 For these applications, they’re really great! 00:10:18.350 --> 00:10:23.209 They are very reliable, are long-lasting (24,000 hours is typical), usually have no trouble 00:10:23.209 --> 00:10:27.360 starting in the coldest of weather conditions, and also they are very color and brightness 00:10:27.360 --> 00:10:28.960 stable over their life. 00:10:28.960 --> 00:10:32.760 They will usually retain 80% of their original brightness by the time they go out. 00:10:32.760 --> 00:10:34.750 And, their color is very consistent. 00:10:34.750 --> 00:10:38.480 You’ve probably seen a parking lot with metal halide lighting, another type of discharge 00:10:38.480 --> 00:10:43.250 lamp, with each fixture a different shade of purple, green, or bluish light. 00:10:43.250 --> 00:10:47.430 Sodium lights generally are all the same looking with little to no variation among them. 00:10:47.430 --> 00:10:50.740 They also benefit from being able to perform a hot restrike. 00:10:50.740 --> 00:10:54.700 See a metal halide lamp cannot be restarted until it cools down nearly completely. 00:10:54.700 --> 00:10:59.230 If there’s a momentary power interruption, it may be 3 to 5 minutes before these lights 00:10:59.230 --> 00:11:02.470 can reignite, and then it will be another minute or two until the light is up to full 00:11:02.470 --> 00:11:03.950 brightness again. 00:11:03.950 --> 00:11:07.960 But high pressure sodium lamps are able to re-strike the arc just a few seconds after 00:11:07.960 --> 00:11:12.050 a brief power interruption, and they come back with nearly their peak intensity. 00:11:12.050 --> 00:11:17.320 It’s actually kind of neat to see the arc form in the arc tube when a hot restrike occurs. 00:11:17.320 --> 00:11:20.600 That said, their end-of-life failure mode is kind of odd. 00:11:20.600 --> 00:11:24.490 Over time, the sodium does react with the aluminum oxide, slowly. 00:11:24.490 --> 00:11:28.770 This causes the voltage required to maintain the arc to rise as they age. 00:11:28.770 --> 00:11:33.260 At a certain point, the arc-sustaining voltage will exceed the voltage the ballast can provide, 00:11:33.260 --> 00:11:34.820 and the light goes out. 00:11:34.820 --> 00:11:37.320 But, once it cools, it can be reignited. 00:11:37.320 --> 00:11:38.810 This process is called cycling. 00:11:38.810 --> 00:11:44.660 A cycling HPS lamp will appear to start normally, but once it reaches full brightness, it goes out. 00:11:44.660 --> 00:11:49.220 After it cools, it fires up again, and then when it reaches full brightness, it goes out. 00:11:49.220 --> 00:11:52.540 This happens over and over again until the lamp is replaced. 00:11:52.540 --> 00:11:56.380 So remember, if you see a sodium light going on and off and on and off, it’s not the 00:11:56.380 --> 00:11:58.530 fixture at fault, it needs a new bulb. 00:11:58.530 --> 00:12:02.590 But in the end, the high pressure sodium lamp is a very efficient, very robust, and very 00:12:02.590 --> 00:12:04.980 effective light source for outdoor applications. 00:12:04.980 --> 00:12:09.600 It is also very low maintenance, with the lamps lasting about 5 years assuming an average 00:12:09.600 --> 00:12:11.910 of 12 hours daily operation. 00:12:11.910 --> 00:12:17.010 So even though their color is… odd and they are slow to warm up, they still make a lot 00:12:17.010 --> 00:12:18.610 of economic sense. 00:12:18.610 --> 00:12:23.240 In recent years, the sodium vapor lamp is starting to be replaced with new LED lamps. 00:12:23.240 --> 00:12:24.420 But should they be? 00:12:24.420 --> 00:12:28.640 (yeah) Current LED technology is only about the same efficiency of old fashioned high 00:12:28.640 --> 00:12:30.040 pressure sodium. 00:12:30.040 --> 00:12:34.910 And with a commonly rated life of 50,000 hours, a drop-in replacement may only last twice 00:12:34.910 --> 00:12:35.910 as long. 00:12:35.910 --> 00:12:38.029 And with a faulty driver it may fail sooner. 00:12:38.029 --> 00:12:40.830 Well, the answer is surprisingly complicated. 00:12:40.830 --> 00:12:45.029 It turns out that lumens aren’t quite the objective measurement they seem to be. 00:12:45.029 --> 00:12:49.640 While the sodium light may have an efficiency of 150 lumens per watt, it might be that in 00:12:49.640 --> 00:12:54.769 nighttime conditions, only a quarter of those lumens actually mean anything to our eyes. 00:12:54.769 --> 00:12:58.670 In my next video, we’ll talk about current research that suggests our knowledge of light 00:12:58.670 --> 00:13:00.160 sensitivity is flawed. 00:13:00.160 --> 00:13:04.310 We’ll also discuss the problems of light pollution and circadian rhythm disruption, 00:13:04.310 --> 00:13:09.450 and how high pressure sodium and new LED lighting solutions are both double edged swords. 00:13:09.450 --> 00:13:11.910 Thanks for watching, I hope you enjoyed the video! 00:13:11.910 --> 00:13:14.790 If this is your first time coming across the channel and you liked what you saw, please 00:13:14.790 --> 00:13:15.830 consider subscribing! 00:13:15.830 --> 00:13:19.870 I’ve put some great links down below that go into the history of discharge lighting, 00:13:19.870 --> 00:13:23.390 along with some other great stuff for you light bulb nerds out there. 00:13:23.390 --> 00:13:26.790 Of course, thank you to everyone who supports this channel on Patreon! 00:13:26.790 --> 00:13:29.220 Patrons of the channel are who keep these videos coming. 00:13:29.220 --> 00:13:32.610 If you’d like to join these amazing folks that support what I do, why not take a peek 00:13:32.610 --> 00:13:34.230 at my Patreon page. 00:13:34.230 --> 00:13:36.779 Thanks for your consideration, and I’ll see you next time! 00:13:36.779 --> 00:13:40.431 For the thousands of people, I’m sure, that were wondering how I got the sodium light 00:13:40.431 --> 00:13:44.760 to work in a table lamp--this ballast is wired into an extension cord. 00:13:44.760 --> 00:13:49.920 As far as it knows, this plug is the lamp, this plug is its power supply. 00:13:49.920 --> 00:13:53.060 Not exactly the safest thing in the world but, it does work!