1 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 2 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 3 00:00:08,670 --> 00:00:11,790 want to call it glow common in street lighting. 4 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 5 00:00:16,360 --> 00:00:17,619 to be used widely. 6 00:00:17,619 --> 00:00:19,400 But, why that color? 7 00:00:19,400 --> 00:00:21,820 Well, it’s special kind of light bulb. 8 00:00:21,820 --> 00:00:23,919 Thanks for watching, I hope you enjoyed the video. 9 00:00:23,919 --> 00:00:26,460 No, of course we’re gonna go into more detail than that! 10 00:00:26,460 --> 00:00:30,029 Much of the world’s street lighting (and indeed more broadly outdoor lighting) uses 11 00:00:30,029 --> 00:00:32,500 sodium vapor lamp technology. 12 00:00:32,500 --> 00:00:35,040 The most common is high pressure sodium. 13 00:00:35,040 --> 00:00:39,050 This artificial lighting technology is a type of discharge lamp. 14 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 15 00:00:44,140 --> 00:00:45,920 light from electricity. 16 00:00:45,920 --> 00:00:49,720 Among the earliest sources of artificial light is the incandescent light bulb. 17 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 18 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 19 00:00:59,120 --> 00:01:00,120 be wrong. 20 00:01:00,120 --> 00:01:01,989 But its principle of operation is really simple. 21 00:01:01,989 --> 00:01:03,180 Hot things glow. 22 00:01:03,180 --> 00:01:04,370 Make thing hot. 23 00:01:04,370 --> 00:01:06,130 Make thing hot without burning. 24 00:01:06,130 --> 00:01:07,549 Put hot thing in vacuum. 25 00:01:07,549 --> 00:01:09,409 Now that thing can’t burn away. 26 00:01:09,409 --> 00:01:10,409 Light! 27 00:01:10,409 --> 00:01:14,090 By running electric current through a thin wire, that wire will get hot because of resistance 28 00:01:14,090 --> 00:01:15,740 and it will glow. 29 00:01:15,740 --> 00:01:16,790 Tada! 30 00:01:16,790 --> 00:01:20,539 The earliest light bulbs used a carbon filament, but shortly thereafter improvements in the 31 00:01:20,539 --> 00:01:24,819 ability to make tungsten filaments allowed for a brighter and longer-lasting bulb due 32 00:01:24,819 --> 00:01:27,170 to tungsten’s much higher melting point. 33 00:01:27,170 --> 00:01:31,329 I must recommend this video by the Engineer Guy about the tungsten filament lamp. 34 00:01:31,329 --> 00:01:32,329 It’s great. 35 00:01:32,329 --> 00:01:33,579 I’ve put a link down below. 36 00:01:33,579 --> 00:01:36,539 But anyway, incandescent lights aren’t very efficient. 37 00:01:36,539 --> 00:01:40,049 Creating light through incandescence wastes the vast majority of electrical energy on 38 00:01:40,049 --> 00:01:44,439 radiation that isn’t visible light--simply infrared light and heat. 39 00:01:44,439 --> 00:01:48,840 Among the most common ways to measure efficiency is in lumens per watt, and incandescent bulbs 40 00:01:48,840 --> 00:01:51,799 are typically around 10 lumens per watt. 41 00:01:51,799 --> 00:01:56,209 Really efficient halogens and high-powered incandescents can reach 20 lumens per watt, 42 00:01:56,209 --> 00:01:57,209 but it’s still not great. 43 00:01:57,209 --> 00:02:00,460 But a discharge lamp, well that can be very efficient. 44 00:02:00,460 --> 00:02:05,420 When you send an electric discharge--basically a small electric arc--through an ionized gas, 45 00:02:05,420 --> 00:02:06,420 you get light! 46 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 47 00:02:09,700 --> 00:02:11,780 from Wikipedia which explains why. 48 00:02:11,780 --> 00:02:12,780 Ehem. 49 00:02:54,060 --> 00:02:57,870 In layman’s terms, if you create an arc discharge through some gases, then because 50 00:02:57,870 --> 00:03:01,190 of ions and stuff bouncing around, you’ll end up with photons and depending on what 51 00:03:01,190 --> 00:03:05,680 the gas is, these photons will be a specific frequency and thus will produce a specific 52 00:03:05,680 --> 00:03:06,730 color of light. 53 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 54 00:03:10,180 --> 00:03:12,530 of the colors produced by specific gases. 55 00:03:12,530 --> 00:03:16,030 The most common type of discharge lamp is actually the fluorescent lamp. 56 00:03:16,030 --> 00:03:19,810 The glass tubes in fluorescent lamps are filled with an extremely low pressure gas mixture 57 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 58 00:03:24,940 --> 00:03:26,680 the main discharge. 59 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 60 00:03:32,590 --> 00:03:37,430 ultraviolet light, which the phosphors that coat the glass will convert into visible light, 61 00:03:37,430 --> 00:03:41,900 and depending on the phosphors used you can get a very pleasant or very ghastly white 62 00:03:41,900 --> 00:03:44,370 light of various color temperatures. 63 00:03:44,370 --> 00:03:48,140 You can even use colored phosphors to make any color of light you want. 64 00:03:48,140 --> 00:03:51,760 Sodium vapor lamps rather than using mercury use...sodium. 65 00:03:51,760 --> 00:03:52,760 You guessed it! 66 00:03:52,760 --> 00:03:56,870 When sodium is ionized, its discharge is a very distinctive yellow hue with a wavelength 67 00:03:56,870 --> 00:03:59,330 of 589 nanometers. 68 00:03:59,330 --> 00:04:03,480 Low pressure sodium lamps emit light of pretty much just that wavelength. 69 00:04:03,480 --> 00:04:07,880 While useful, and actually the most efficient discharge lamp available, this light is monochromatic 70 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 71 00:04:11,940 --> 00:04:13,710 then it's not great. 72 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, 73 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. 74 00:04:21,610 --> 00:04:24,550 This is a 50 watt high pressure sodium lamp. 75 00:04:24,550 --> 00:04:29,500 This is the second smallest common size, with 35 watts occupying the smallest spot, but 76 00:04:29,500 --> 00:04:32,110 they go all the way up to 1,000 watts. 77 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 78 00:04:36,130 --> 00:04:37,870 don’t know is what rubies are. 79 00:04:37,870 --> 00:04:42,090 Of course this is synthetic, but due to the crazy reactivity of elemental sodium, it needs 80 00:04:42,090 --> 00:04:46,450 to be contained in something that will A) contain it without reacting with it and B) 81 00:04:46,450 --> 00:04:49,940 is quite strong and can withstand a lot of heat. 82 00:04:49,940 --> 00:04:52,220 Aluminum oxide fits the bill perfectly. 83 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. 84 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 85 00:04:59,880 --> 00:05:00,880 vaporizes. 86 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 87 00:05:04,520 --> 00:05:05,620 their output. 88 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. 89 00:05:10,560 --> 00:05:15,660 Due to an arc discharge having negative resistance, as current goes up, resistance goes down, 90 00:05:15,660 --> 00:05:19,930 and power consumed will just skyrocket without a ballast or choke to stop it from destroying 91 00:05:19,930 --> 00:05:20,930 itself. 92 00:05:20,930 --> 00:05:23,770 The ballast will have either two or three components. 93 00:05:23,770 --> 00:05:27,470 First is the actual ballast itself which is similar in construction to a transformer, 94 00:05:27,470 --> 00:05:31,520 then there is the ignitor which is needed to start the lamp, and some ballasts including 95 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 96 00:05:36,680 --> 00:05:39,520 brought about by the inductive nature of the ballast. 97 00:05:39,520 --> 00:05:43,460 As with many discharge lamps, high pressure sodium lamps generally go through a distinct 98 00:05:43,460 --> 00:05:44,930 warmup routine. 99 00:05:44,930 --> 00:05:48,170 When first powered on, the ignitor is working to strike the arc. 100 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. 101 00:05:52,870 --> 00:05:56,260 Quickly the mercury starts to vaporize, and as it does so the ionization of the mercury 102 00:05:56,260 --> 00:06:00,430 vapor releases a pale blue color, often appearing as grey. 103 00:06:00,430 --> 00:06:03,970 But then the distinctive yellow of the sodium discharge takes over. 104 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. 105 00:06:10,150 --> 00:06:13,040 This is what the light from low pressure sodium lamps looks like. 106 00:06:13,040 --> 00:06:16,730 But then the high pressure in high pressure sodium does its thing. 107 00:06:16,730 --> 00:06:20,710 The arc tube is very small, and the gases inside it become quite hot. 108 00:06:20,710 --> 00:06:24,930 In a space of given volume, with increased temperature comes increased pressure. 109 00:06:24,930 --> 00:06:29,590 This results in a phenomenon called pressure broadening, which causes ordinarily weak spectral 110 00:06:29,590 --> 00:06:34,460 emissions to become stronger, and thus the lamp emits more wavelengths of light. 111 00:06:34,460 --> 00:06:38,570 Once completely warmed up, the pressure broadening causes the light to appear less yellow and 112 00:06:38,570 --> 00:06:42,440 more white, though still with a prominent yellow cast. 113 00:06:42,440 --> 00:06:46,850 Color perception is subjective, but I’d call this a orangey-peachy-gold color with 114 00:06:46,850 --> 00:06:48,080 a hint of pink. 115 00:06:48,080 --> 00:06:49,080 You are… you, 116 00:06:49,080 --> 00:06:49,980 yes? 117 00:06:50,680 --> 00:06:51,720 You are warming up right, 118 00:06:51,720 --> 00:06:53,060 you’re on? 119 00:06:57,560 --> 00:06:58,560 OK Good. 120 00:06:58,570 --> 00:07:01,750 This is the most exciting part of the video, I guarantee it. 121 00:07:01,750 --> 00:07:05,000 I bet you’ve never had a video more exciting than this one. 122 00:07:06,220 --> 00:07:08,699 I don’t even know what this looks like on camera. 123 00:07:08,699 --> 00:07:10,070 So we’ll, we’ll just. 124 00:07:10,070 --> 00:07:11,670 I should--I should have looked into that! 125 00:07:11,670 --> 00:07:12,670 Yeah. 126 00:07:12,670 --> 00:07:13,860 That was good. 127 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, 128 00:07:18,060 --> 00:07:19,750 just like its arc. 129 00:07:19,750 --> 00:07:20,750 Ha! 130 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 131 00:07:25,150 --> 00:07:29,430 have an HPS bulb in any ordinary setting), you can tell that it’s much brighter. 132 00:07:29,430 --> 00:07:33,570 For half the energy of its incandescent equivalent, it’s producing about triple the light, going 133 00:07:33,570 --> 00:07:34,830 off lumens. 134 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 135 00:07:39,889 --> 00:07:40,889 incandescent. 136 00:07:40,889 --> 00:07:43,940 Some high pressure sodiums lamps are nearly twice as efficient as this one, producing 137 00:07:43,940 --> 00:07:45,790 150 lumens per watt. 138 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 139 00:07:50,090 --> 00:07:52,960 to travel farther than that of the “incandescent”. 140 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 141 00:07:56,520 --> 00:07:58,479 a standard white light. 142 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, 143 00:08:02,500 --> 00:08:06,100 closely matching the peak sensitivity of the cells in our eyes. 144 00:08:06,100 --> 00:08:09,020 But only under photopic, daylight conditions. 145 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 146 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. 147 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. 148 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 149 00:08:29,800 --> 00:08:32,360 source for general household illumination. 150 00:08:32,360 --> 00:08:36,080 Every artificial light source has what’s called a CRI, or color rendering index. 151 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, 152 00:08:42,310 --> 00:08:43,980 which the sun has. 153 00:08:43,980 --> 00:08:49,200 Incandescent lights has a CRI of 99, but most other light sources aren’t so high. 154 00:08:49,210 --> 00:08:53,430 Poor CRI plagued many fluorescent light sources, particularly early ones. 155 00:08:53,430 --> 00:08:57,640 Though the light of a CFL might appear perfectly white, the colors of objects underneath it 156 00:08:57,640 --> 00:08:59,240 might seem a little off. 157 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 158 00:09:05,200 --> 00:09:07,600 some colors to appear oddly. 159 00:09:07,600 --> 00:09:12,750 The average high pressure sodium lamps has a color rendering index of about, drumroll please. 160 00:09:12,750 --> 00:09:13,780 21. 161 00:09:14,320 --> 00:09:15,380 It’s pretty bad. 162 00:09:15,390 --> 00:09:18,839 Here’s an assortment of colorful objects as lit by normal white light. 163 00:09:18,839 --> 00:09:22,130 And now, observe how they look under high pressure sodium. 164 00:09:22,130 --> 00:09:25,390 I’ll show them as it warms up, because it demonstrates how when the sodium emission 165 00:09:25,390 --> 00:09:28,470 first comes into play, it is almost monochromatic. 166 00:09:28,470 --> 00:09:31,710 See how you can barely tell what color things are supposed to be? 167 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. 168 00:09:37,160 --> 00:09:40,750 The strangest-looking object I discovered was this can of La Croix. 169 00:09:40,750 --> 00:09:42,500 Take a look at this side by side. 170 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. 171 00:09:47,860 --> 00:09:50,080 Food in general looks… 172 00:09:50,080 --> 00:09:52,649 unappetizing under high pressure sodium lighting. 173 00:09:52,649 --> 00:09:53,970 Pasta and red sauce? 174 00:09:53,970 --> 00:09:56,920 The sauce will look more of a pukey-brown. 175 00:09:56,920 --> 00:09:58,310 Having some yellow tortilla chips? 176 00:09:58,310 --> 00:10:00,529 Yeah they’re more of a chartreuse now. 177 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 178 00:10:03,871 --> 00:10:07,570 suited for general illumination where they’ll run all night. 179 00:10:07,570 --> 00:10:11,610 So, street lights, parking lots, security lighting, and other dusk-to-dawn applications 180 00:10:11,610 --> 00:10:13,830 are where these lamps really shine. 181 00:10:13,830 --> 00:10:16,370 I came up with that all on my own. 182 00:10:16,370 --> 00:10:18,350 For these applications, they’re really great! 183 00:10:18,350 --> 00:10:23,209 They are very reliable, are long-lasting (24,000 hours is typical), usually have no trouble 184 00:10:23,209 --> 00:10:27,360 starting in the coldest of weather conditions, and also they are very color and brightness 185 00:10:27,360 --> 00:10:28,960 stable over their life. 186 00:10:28,960 --> 00:10:32,760 They will usually retain 80% of their original brightness by the time they go out. 187 00:10:32,760 --> 00:10:34,750 And, their color is very consistent. 188 00:10:34,750 --> 00:10:38,480 You’ve probably seen a parking lot with metal halide lighting, another type of discharge 189 00:10:38,480 --> 00:10:43,250 lamp, with each fixture a different shade of purple, green, or bluish light. 190 00:10:43,250 --> 00:10:47,430 Sodium lights generally are all the same looking with little to no variation among them. 191 00:10:47,430 --> 00:10:50,740 They also benefit from being able to perform a hot restrike. 192 00:10:50,740 --> 00:10:54,700 See a metal halide lamp cannot be restarted until it cools down nearly completely. 193 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 194 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 195 00:11:02,470 --> 00:11:03,950 brightness again. 196 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 197 00:11:07,960 --> 00:11:12,050 a brief power interruption, and they come back with nearly their peak intensity. 198 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. 199 00:11:17,320 --> 00:11:20,600 That said, their end-of-life failure mode is kind of odd. 200 00:11:20,600 --> 00:11:24,490 Over time, the sodium does react with the aluminum oxide, slowly. 201 00:11:24,490 --> 00:11:28,770 This causes the voltage required to maintain the arc to rise as they age. 202 00:11:28,770 --> 00:11:33,260 At a certain point, the arc-sustaining voltage will exceed the voltage the ballast can provide, 203 00:11:33,260 --> 00:11:34,820 and the light goes out. 204 00:11:34,820 --> 00:11:37,320 But, once it cools, it can be reignited. 205 00:11:37,320 --> 00:11:38,810 This process is called cycling. 206 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. 207 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. 208 00:11:49,220 --> 00:11:52,540 This happens over and over again until the lamp is replaced. 209 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 210 00:11:56,380 --> 00:11:58,530 fixture at fault, it needs a new bulb. 211 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 212 00:12:02,590 --> 00:12:04,980 effective light source for outdoor applications. 213 00:12:04,980 --> 00:12:09,600 It is also very low maintenance, with the lamps lasting about 5 years assuming an average 214 00:12:09,600 --> 00:12:11,910 of 12 hours daily operation. 215 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 216 00:12:17,010 --> 00:12:18,610 of economic sense. 217 00:12:18,610 --> 00:12:23,240 In recent years, the sodium vapor lamp is starting to be replaced with new LED lamps. 218 00:12:23,240 --> 00:12:24,420 But should they be? 219 00:12:24,420 --> 00:12:28,640 (yeah) Current LED technology is only about the same efficiency of old fashioned high 220 00:12:28,640 --> 00:12:30,040 pressure sodium. 221 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 222 00:12:34,910 --> 00:12:35,910 as long. 223 00:12:35,910 --> 00:12:38,029 And with a faulty driver it may fail sooner. 224 00:12:38,029 --> 00:12:40,830 Well, the answer is surprisingly complicated. 225 00:12:40,830 --> 00:12:45,029 It turns out that lumens aren’t quite the objective measurement they seem to be. 226 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 227 00:12:49,640 --> 00:12:54,769 nighttime conditions, only a quarter of those lumens actually mean anything to our eyes. 228 00:12:54,769 --> 00:12:58,670 In my next video, we’ll talk about current research that suggests our knowledge of light 229 00:12:58,670 --> 00:13:00,160 sensitivity is flawed. 230 00:13:00,160 --> 00:13:04,310 We’ll also discuss the problems of light pollution and circadian rhythm disruption, 231 00:13:04,310 --> 00:13:09,450 and how high pressure sodium and new LED lighting solutions are both double edged swords. 232 00:13:09,450 --> 00:13:11,910 Thanks for watching, I hope you enjoyed the video! 233 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 234 00:13:14,790 --> 00:13:15,830 consider subscribing! 235 00:13:15,830 --> 00:13:19,870 I’ve put some great links down below that go into the history of discharge lighting, 236 00:13:19,870 --> 00:13:23,390 along with some other great stuff for you light bulb nerds out there. 237 00:13:23,390 --> 00:13:26,790 Of course, thank you to everyone who supports this channel on Patreon! 238 00:13:26,790 --> 00:13:29,220 Patrons of the channel are who keep these videos coming. 239 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 240 00:13:32,610 --> 00:13:34,230 at my Patreon page. 241 00:13:34,230 --> 00:13:36,779 Thanks for your consideration, and I’ll see you next time! 242 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 243 00:13:40,431 --> 00:13:44,760 to work in a table lamp--this ballast is wired into an extension cord. 244 00:13:44,760 --> 00:13:49,920 As far as it knows, this plug is the lamp, this plug is its power supply. 245 00:13:49,920 --> 00:13:53,060 Not exactly the safest thing in the world but, it does work!