WEBVTT Kind: captions Language: en 00:00:00.000 --> 00:00:04.280 If you’ve ever wondered how street lights know that it’s dark outside, 00:00:04.280 --> 00:00:08.110 well there’s a good chance it’s thanks to one of these. 00:00:08.110 --> 00:00:10.937 This is a photocell light control. 00:00:10.937 --> 00:00:15.385 It has a light sensor on its side and a few electrical connections on the bottom, 00:00:15.385 --> 00:00:21.316 and when wired appropriately into a light fixture, it will prevent that light from coming on when the sun’s up 00:00:21.316 --> 00:00:23.460 (and turn it on when the sun sets). 00:00:24.300 --> 00:00:28.368 But… how exactly is it doing that? 00:00:28.368 --> 00:00:31.720 Simply saying “a light sensor turns the light off” 00:00:31.720 --> 00:00:36.000 doesn’t really explain what’s actually going on inside of here, does it? 00:00:36.364 --> 00:00:39.420 After all, what even is a sensor? 00:00:40.200 --> 00:00:47.758 Perhaps that sounds like a silly question, but the thing inside of this that actually turns on and off the light it controls… 00:00:48.000 --> 00:00:49.607 is a thermostat. 00:00:50.040 --> 00:00:55.722 Yeah, this thing is a little more rube-goldbergy than it might seem at first glance. 00:00:55.722 --> 00:00:59.995 The actual light sensing doodad is likely a familiar sight. 00:00:59.995 --> 00:01:08.616 Take a look at a common night light and you’ll find a smaller but very similar looking component under this bit of clear plastic. 00:01:08.616 --> 00:01:14.922 The squiggly dark orange line through a shiny metal plate is the tell-tale of a photoresistor, 00:01:14.922 --> 00:01:20.264 an electronic component also known as a light-dependent resistor or LDR. 00:01:20.264 --> 00:01:27.240 As its name might suggest, the electrical resistance of this component changes based on the amount of light that hits it. 00:01:28.020 --> 00:01:32.900 We can see this in action if I take this  apart and hook up a multimeter. 00:01:32.900 --> 00:01:38.503 Notice that as more light hits the photoresistor, the measured resistance decreases. 00:01:38.503 --> 00:01:45.293 In other words, the more light that hits it, the more easily electric current can flow through this component. 00:01:46.560 --> 00:01:51.594 You might have realized that  this is backwards to the goal of a nightlight - 00:01:51.594 --> 00:01:54.431 the nightlight should come on when it’s dark, 00:01:54.431 --> 00:02:00.060 and the photoresistor on its own would make it harder to light the bulb at night and easier during the day. 00:02:00.780 --> 00:02:05.880 Accordingly, the photoresistor is only part of the equation - hence the circuit board. 00:02:06.420 --> 00:02:11.880 In addition to the photoresistor, there’s  also an ordinary resistor and a thyristor.   00:02:12.540 --> 00:02:17.233 This trio of istors is what actually makes the circuit function. 00:02:17.233 --> 00:02:23.273 Power flows in from the live pin and up through this bit of copper which passes for a lamp holder these days. 00:02:23.580 --> 00:02:26.784 Once it’s made it through the filament of the incandescent bulb, 00:02:26.784 --> 00:02:32.536 it comes back down this other bit of copper and hits one side of the thyristor. 00:02:32.536 --> 00:02:36.787 That thyristor is a semiconductor which serves both as a diode 00:02:36.787 --> 00:02:41.413 (meaning it only allows current to flow through it in one direction, which, fun fact, 00:02:41.413 --> 00:02:46.586 has the side-effect of only running the lamp at half-power which’ll greatly extend its life) 00:02:46.586 --> 00:02:56.580 but also, and more importantly, it serves as a power switch, interrupting the circuit and preventing the lamp from lighting unless it sees a control input. 00:02:57.720 --> 00:03:02.664 This is pretty confusing to look at so I’ve drawn this as a circuit diagram. 00:03:02.664 --> 00:03:08.370 What we really have here is an ordinary lamp circuit with  the thyristor interrupting it in the middle.   00:03:08.940 --> 00:03:12.521 As drawn, this would never light the bulb. 00:03:12.521 --> 00:03:19.462 But if we provide an input by way of a bit of current flowing to the gate of the thyristor, that’s its middle pin, 00:03:19.462 --> 00:03:25.740 then it will relax and allow current to flow from one side to the other, which will complete the circuit and light the lamp. 00:03:26.700 --> 00:03:30.620 That activation current comes from the resistor here. 00:03:30.620 --> 00:03:36.249 It provides a path for current to flow between this point and the thyristor’s gate. 00:03:36.249 --> 00:03:43.283 With this in the circuit by itself, now the light will never go out (assuming the bulb isn’t burnt out). 00:03:43.283 --> 00:03:49.200 The resistor will always provide enough current for the thyristor to activate and allow the light to turn on. 00:03:50.100 --> 00:03:54.839 However, that resistor is a 2 megaohm resistor. 00:03:54.839 --> 00:04:02.160 It lets a tiny, tiny amount of current through itself, in fact barely enough to activate the thyristor.   00:04:02.453 --> 00:04:08.820 It would thus be very easy to disrupt that input,  which is precisely what the photoresistor is for. 00:04:09.600 --> 00:04:15.403 Notice that it’s connected between the neutral pin of the plug and this point here. 00:04:15.403 --> 00:04:16.935 When it’s dark enough, 00:04:16.935 --> 00:04:24.639 the resistance of the photoresistor is sufficiently high to where it doesn’t affect anything about the circuit and the lamp lights. 00:04:24.639 --> 00:04:28.709 But when light hits it, its resistance falls. 00:04:28.709 --> 00:04:35.611 Once it’s low enough, it provides an alternative path for that activation current coming from the resistor to take, 00:04:35.611 --> 00:04:41.161 so that current bypasses the thyristor’s gate and the lamp doesn't light. 00:04:41.161 --> 00:04:42.000 It's pretty simple. 00:04:42.600 --> 00:04:50.093 Because of the way this circuit works, some current is always flowing - but it’s hardly any at all. 00:04:50.093 --> 00:04:58.338 That 2 megaohm resistor, at 120V, dissipates a whole 0.0072 watts. 00:04:58.338 --> 00:05:00.885 And that’s assuming it's wired directly to neutral. 00:05:00.885 --> 00:05:06.936 Which it isn’t - it’s in series with the lamp filament, which adds another 400 ohms or so. 00:05:06.936 --> 00:05:12.268 The thyristor needs absolutely miniscule amounts of current to become activated, 00:05:12.268 --> 00:05:19.429 so while this circuit is technically drawing a little power during the day, it’s practically zero. 00:05:19.429 --> 00:05:27.661 Also noteworthy, thyristors exhibit a sort-of latching behavior and, once activated with sufficient current flowing through the gate, 00:05:27.661 --> 00:05:32.540 stay activated until the zero-crossing of the AC power cycle. 00:05:32.540 --> 00:05:38.693 This is why the lamp will fade to life as it gets dark rather than just snap to full brightness. 00:05:38.693 --> 00:05:43.980 When most but not all of the activation current bypasses through the photoresistor, 00:05:43.980 --> 00:05:51.180 the thyristor will periodically kick the lamp to life at the tail end of each power cycle,  behaving much like a dimmer switch does. 00:05:51.720 --> 00:05:57.600 This circuit is really quite elegant and it works just fine for controlling a tiny little light bulb.   00:05:58.140 --> 00:06:01.794 But it’s not enough to control a street light 00:06:01.794 --> 00:06:04.980 which might have a lightbulb like this - 00:06:04.980 --> 00:06:08.507 and this thing draws 1,000 watts. 00:06:08.507 --> 00:06:11.747 For this, you’re gonna need something a lot more robust. 00:06:11.747 --> 00:06:14.105 Like the thing I showed you at the beginning. 00:06:14.105 --> 00:06:19.801 This light control can interrupt the full 15 amps of a standard US lighting circuit, 00:06:19.801 --> 00:06:23.822 and in fact is even rated for up to 277 volts. 00:06:23.822 --> 00:06:31.585 This style, with its twist-lock plug, is commonly used atop individual light fixtures and meant for easy replacement, 00:06:31.585 --> 00:06:38.003 but they’re also available in little modules like this that  you wire into whatever you want to control. 00:06:38.700 --> 00:06:41.451 There are two important things to note about these things: 00:06:41.451 --> 00:06:47.735 First, the photoresistors on them are a lot larger than what we see in the nightlight. 00:06:47.735 --> 00:06:51.764 And second, both of them have three electrical connections. 00:06:51.764 --> 00:06:57.713 There’s the incoming power, the switched outgoing power, and neutral as well. 00:06:57.713 --> 00:07:06.770 That tells us that the photocontrols operate independently of the loads they control, and likely consume a little bit of power themselves. 00:07:06.770 --> 00:07:12.808 Now you might think that there’s some sort of logic circuitry in these things controlling a relay or something, 00:07:12.808 --> 00:07:16.651 but their operation is in fact much simpler than that. 00:07:17.434 --> 00:07:19.128 Let’s pop the cover off this one. 00:07:19.500 --> 00:07:21.839 It’s pretty empty in here, isn’t it? 00:07:21.839 --> 00:07:29.014 We just have the photoresistor on a little mounting plate, then some kind of component touching a small circuit board. 00:07:29.014 --> 00:07:36.186 It’s clear that this component is the actual switch as it has fairly large wires connected to either side of it, 00:07:36.186 --> 00:07:39.019 but what do you suppose is going on beneath it? 00:07:39.019 --> 00:07:45.106 That little board has a lead going to the incoming power, and another going to the photoresistor. 00:07:45.106 --> 00:07:48.829 Then the other side of the photoresistor is wired straight to the neutral pin. 00:07:49.730 --> 00:07:54.120 To get a better idea of what’s going on, let’s remove that mystery component. 00:07:55.020 --> 00:07:58.140 Betcha didn’t think we’d find thermal paste in this thing, did ya? 00:07:58.680 --> 00:08:02.940 If you’ve ever done any sort of appliance repair, you might recognize this thing. 00:08:03.480 --> 00:08:06.026 This is a thermostatic switch. 00:08:06.026 --> 00:08:09.360 Normally it’s closed and will allow power to flow through. 00:08:10.020 --> 00:08:15.234 But inside of it there’s a bimetallic disc which will deform as temperature rises. 00:08:15.234 --> 00:08:15.895 [click] 00:08:15.895 --> 00:08:21.690 Once it’s past a certain temperature, that disc will snap and open the switch contacts inside. 00:08:22.500 --> 00:08:31.109 You often find these used as safety switches in appliances that produce a lot of heat, like clothes dryers or gas-fired furnaces. 00:08:31.109 --> 00:08:38.820 In those applications they might be called limit switches, and they’re designed to shut the appliance down if things are getting too hot. 00:08:39.600 --> 00:08:41.566 What’s it doing in here? 00:08:41.566 --> 00:08:48.035 Well, before I removed it it was pressing against this little circuit board with a little thermal paste in between. 00:08:48.035 --> 00:08:52.121 That circuit board has nothing on it but a couple of surface-mount resistors 00:08:52.121 --> 00:08:56.785 (as well as a PTC thermistor to serve as a fuse, but that’s not important right now). 00:08:56.785 --> 00:09:02.735 Those resistors are doing the simplest job a resistor can possibly do - produce heat. 00:09:03.636 --> 00:09:07.200 That’s right, this circuit board is functioning as a heater. 00:09:07.920 --> 00:09:11.801 Surface mount resistors are certainly an unconventional heating element,   00:09:11.801 --> 00:09:15.060 but that’s what they’re doing and they’re  doing a bang-up job, too, so don’t judge. 00:09:15.660 --> 00:09:18.479 But notice how that heater circuit is wired. 00:09:18.479 --> 00:09:24.600 It’s across live and neutral, but it makes a little diversion through our friend the photoresistor. 00:09:24.600 --> 00:09:29.669 Knowing what we’ve learned about photoresistors, think about what that would do. 00:09:29.669 --> 00:09:32.995 If I wire this up and we take a look with a thermal camera, 00:09:32.995 --> 00:09:39.070 in a dark room we can see that the heater is on,  but it’s just a little warm. 00:09:39.070 --> 00:09:46.000 It’s trying to heat up, but the photoresistor is in a state of high resistance, preventing power from flowing. 00:09:46.000 --> 00:09:53.028 When I shine a light onto the photoresistor, though, its resistance falls and the heater immediately gets warmer - 00:09:53.028 --> 00:09:55.759 in fact it gets pretty hot. 00:09:55.759 --> 00:10:00.760 So we have a heater circuit that gets hotter when more light hits this thing, 00:10:00.760 --> 00:10:05.633 and we have a limit switch that opens a circuit when it gets too hot. 00:10:06.540 --> 00:10:08.885 I wonder what would happen if we put them toget— 00:10:08.885 --> 00:10:11.220 oh, right, that's how it was when I got it. 00:10:11.820 --> 00:10:15.769 With it reassembled, here’s what we see in the thermal camera. 00:10:15.769 --> 00:10:20.894 Again, when powered on in the dark, we can see the faintest little hot-spot. 00:10:20.894 --> 00:10:26.616 But when I shine a light on the photoresistor, that hot spot gets bigger and... 00:10:26.616 --> 00:10:27.817 hot. 00:10:27.817 --> 00:10:31.983 The resistors on that board are dissipating about 2.5 watts, 00:10:31.983 --> 00:10:36.120 and the thermal paste is transferring that heat energy into the face of the thermal switch. 00:10:37.223 --> 00:10:40.226 The switch remains closed for about 2 minutes, 00:10:40.226 --> 00:10:41.082 but eventually 00:10:41.082 --> 00:10:41.767 [click] 00:10:41.767 --> 00:10:42.427 it opens. 00:10:43.200 --> 00:10:47.848 One thing to note is that the photoresistor is also a resistor in the circuit 00:10:47.848 --> 00:10:50.532 so it, too, dissipates a bit of heat. 00:10:50.532 --> 00:10:56.580 However, the big metal plate it’s mounted on doubles as a heat sink, so it’s barely visible to the thermal camera. 00:10:57.360 --> 00:11:02.335 I’ve wired up this totally-legit streetlight in a definitely-not-sketchy fashion 00:11:02.335 --> 00:11:06.244 to provide a demonstration of the photocontrol in action. 00:11:06.244 --> 00:11:15.120 Right now, the sun is up, so the photoresistor is letting enough current through to keep the heater powered and the thermostatic switch nice and toasty.   00:11:15.458 --> 00:11:22.868 But as we approach sundown, the heater slowly loses power as the photoresistor’s resistance increases, 00:11:22.868 --> 00:11:25.537 and thus its heat output falls. 00:11:25.537 --> 00:11:29.882 In this... simulated sunset, the heater instantly shuts off, 00:11:29.882 --> 00:11:32.700 but it takes a while for the thermostatic switch to cool down. 00:11:33.420 --> 00:11:37.551 Once it does, the switch will close, and the light turns on. 00:11:37.551 --> 00:11:38.418 [click] 00:11:38.418 --> 00:11:40.048 Ah, there we are. 00:11:40.048 --> 00:11:47.322 The delay is actually quite useful, especially for lighting technologies like the high pressure sodium lamp you see here. 00:11:47.322 --> 00:11:52.048 Ideally, you want to minimize the number of times these lamps start up, 00:11:52.048 --> 00:12:00.319 and the varying lighting conditions as the sun rises and sets could result in some wild behavior at dawn and dusk. 00:12:00.319 --> 00:12:06.087 The thermal mass of the thermostatic switch, along with its deadband between activation temperatures, 00:12:06.087 --> 00:12:13.353 provides the perfect combination of delay factors to ensure the light it controls doesn’t behave erratically. 00:12:14.006 --> 00:12:17.993 Some people would really like me to say the word “hysteresis.” 00:12:17.993 --> 00:12:18.833 You’re welcome! 00:12:19.200 --> 00:12:24.466 Now, earlier I said the resistors in here dissipate about 2 and a half watts. 00:12:24.466 --> 00:12:32.055 That means that, ironically, this thing consumes power in order to save power. 00:12:32.055 --> 00:12:38.627 Since the smallest lamp one of these might control is about 50 watts, it’s still definitely worth having one of these. 00:12:38.627 --> 00:12:39.304 [click] 00:12:39.304 --> 00:12:44.463 But putting one on top of every light fixture doesn’t always make sense. 00:12:44.463 --> 00:12:47.800 Not only does that make each light fixture more expensive, 00:12:47.800 --> 00:12:52.668 but it also means every single one is consuming a little bit of power all the time 00:12:52.668 --> 00:12:54.383 and that adds up. 00:12:54.383 --> 00:12:59.269 So in many cases, banks of streetlights are wired to a central location, 00:12:59.269 --> 00:13:04.380 and a single one of these things is used to control a contactor at the distribution point. 00:13:05.220 --> 00:13:10.980 The fact that these need power to turn things off also adds a fun little side-effect. 00:13:11.700 --> 00:13:18.443 The switch inside closes because the heater stopped heating, which usually happens because the sun set, 00:13:18.443 --> 00:13:20.160 but that’s not the only reason it can happen! 00:13:20.880 --> 00:13:24.290 If, for example, there's a power outage during the day, 00:13:24.290 --> 00:13:31.620 the switches inside every one of these things will cool down and close within just a few minutes despite the sun shining brightly.   00:13:32.340 --> 00:13:34.840 So when power comes back on, 00:13:34.840 --> 00:13:38.686 all those streetlights (and anything else controlled by one of these) 00:13:38.686 --> 00:13:45.761 will also come on for a minute or two before the internal heater warms up enough to shut them off again. 00:13:46.279 --> 00:13:49.020 I mean, it’s pretty inconsequential, really, but it’s still fun. 00:13:49.680 --> 00:13:56.251 Something notable about this photocontrol is that its design is actually quite a bit different from designs of the past, 00:13:56.251 --> 00:14:00.000 which you can perhaps tell by the massive lack of stuff inside of it. 00:14:00.720 --> 00:14:05.180 This is an old, standardized form-factor so the casing didn’t change 00:14:05.180 --> 00:14:10.680 but older versions often had something similar to what  we find inside this wire-in module.   00:14:11.400 --> 00:14:14.606 In practice, this is the same exact thing, 00:14:14.606 --> 00:14:22.221 with a photoresistor wired in-series with a resistor that acts as a heater, only allowing that heater to function during the day. 00:14:22.221 --> 00:14:25.329 But instead of heating an off-the-shelf limit switch, 00:14:25.329 --> 00:14:27.360 it heats this bimetallic bar. 00:14:28.140 --> 00:14:35.852 As it warms up, the bar starts bending downward and applying force to a spring-loaded switch contact through this screw. 00:14:35.852 --> 00:14:40.860 Once it’s warm enough (and thus bent enough), that switch contact snaps open. 00:14:41.820 --> 00:14:45.360 And on this particular module, it barely opens.   00:14:45.900 --> 00:14:48.230 Which is actually pretty disconcerting. 00:14:48.230 --> 00:14:53.227 But whatever, once the sun sets and the photoresistor restricts flow through the heater, 00:14:53.227 --> 00:15:00.115 the bar starts to cool back down, move back to its original shape, and eventually the switch contacts snap together again. 00:15:00.993 --> 00:15:07.965 Older versions of this puck-style twist-lock thingamajig  often had a very similar mechanism to this inside, 00:15:07.965 --> 00:15:13.560 perhaps with more robust contacts for handling  the inductive load of a big magnetic ballast. 00:15:14.340 --> 00:15:18.300 It’s not much of a surprise that this new one uses a limit switch, honestly, 00:15:18.300 --> 00:15:23.490 because that’s an off-the-shelf part used in gajillions of applications. 00:15:23.490 --> 00:15:30.334 The bimetallic bendy switch mechanism with a resistor taped to the bar  needs purpose-built parts. 00:15:30.334 --> 00:15:35.760 It also seems rather fiddly to put together, and it looks as though the screw tension needed calibration in the factory.   00:15:36.960 --> 00:15:42.220 This design, on the other hand, is a three-component circuit board which probably cost a few pennies, 00:15:42.220 --> 00:15:47.320 a dab of thermal paste, an off-the-shelf limit switch, and some screws. 00:15:47.320 --> 00:15:50.040 Wire in the photoresistor and you’re done. 00:15:50.603 --> 00:15:53.433 Is this as robust as the old designs? 00:15:54.198 --> 00:15:55.200 Who knows. 00:15:55.500 --> 00:15:59.295 But this surely isn’t the only way to handle this, is it? 00:15:59.295 --> 00:16:03.428 I mean, with microprocessor chips cheap as chips these days, 00:16:03.428 --> 00:16:13.245 wouldn’t a little code running on a microcontroller powering a relay make more sense than a heater running all day just to keep a thermostatic switch open? 00:16:13.980 --> 00:16:16.703 Well, take a look at this little fella. 00:16:16.703 --> 00:16:19.196 It’s like a baby version of the other one! 00:16:19.196 --> 00:16:23.040 And its photoresistor looks pretty small,  not much bigger than the night light’s. 00:16:23.820 --> 00:16:25.423 Let’s take a look inside. 00:16:26.234 --> 00:16:27.276 Oh. 00:16:27.276 --> 00:16:30.300 It literally is just a baby version of the other one. 00:16:31.320 --> 00:16:36.480 That actually surprised me quite a lot, but I guess it proves that if it ain’t broke… 00:16:36.480 --> 00:16:40.220 Perhaps there are more power-efficient ways to handle this task, 00:16:40.220 --> 00:16:42.078 in fact I’m certain there are. 00:16:42.078 --> 00:16:44.600 But, they all have trade-offs. 00:16:44.600 --> 00:16:51.675 Any solution involving a microcontroller is gonna need its own power supply to function which adds  costs. 00:16:51.675 --> 00:16:57.541 And then you’re gonna be sticking that thing on top of a light pole with the sun beating down on it day after day. 00:16:57.541 --> 00:17:00.556 Capacitors tend to not like that. 00:17:00.556 --> 00:17:05.942 Plus, then you’re gonna need to figure out a way to introduce hysteresis in software, 00:17:05.942 --> 00:17:08.548 and if there’s one thing I know about software, it’s 00:17:08.638 --> 00:17:09.982 [sound locks up] 00:17:09.982 --> 00:17:10.482 pre 00:17:10.842 --> 00:17:11.489 ee, and oft 00:17:11.827 --> 00:17:13.208 half baked. 00:17:13.560 --> 00:17:18.239 There is definitely something to be said for a simple solution like this, 00:17:18.239 --> 00:17:25.380 and besides, the power they consume is minimal - especially when you use one to control 100 light poles. 00:17:25.980 --> 00:17:28.894 What I think is most interesting about these things 00:17:28.894 --> 00:17:35.894 is they are a perfect demonstration of how to turn an electronic component into something that’s actually useful. 00:17:35.894 --> 00:17:41.015 It’s one thing to learn what a photoresistor does, 00:17:41.015 --> 00:17:43.680 and quite another to make something happen with it. 00:17:44.220 --> 00:17:47.142 And there’s more than one way to go about it! 00:17:47.142 --> 00:17:52.923 The nightlight shows an elegant semiconductor-based solution for low-power applications. 00:17:52.923 --> 00:17:58.781 And while turning a heater on and off with the sun might seem pretty off-the-wall, 00:17:58.781 --> 00:18:02.820 when you know that bimetallic strips get all bendy when they heat up, 00:18:03.420 --> 00:18:06.060 that presents an opportunity for actuating a switch.   00:18:06.960 --> 00:18:13.334 All that it takes to turn that into a useful product is for someone to make the connection. 00:18:14.235 --> 00:18:16.889 ♫ painfully smooth jazz ♫ 00:18:18.240 --> 00:18:21.114 The thing inside of here… hooh 00:18:21.114 --> 00:18:23.339 You’re gonna need something a lot more robust. 00:18:23.339 --> 00:18:25.800 Like the thing I showed you [clunk] at the begin--- crap! 00:18:27.480 --> 00:18:28.633 [frustration noises] 00:18:28.633 --> 00:18:30.139 ...and the lamp lights. 00:18:30.139 --> 00:18:34.320 But when light falls on it, its resistance falls. When 00:18:36.180 --> 00:18:40.140 Surface-mount resistors are certainly an  unconventional heating element but they're, but  00:18:41.160 --> 00:18:44.649 With a photoresistor wired in series with a res -- 00:18:44.649 --> 00:18:45.403 crap! 00:18:45.403 --> 00:18:47.294 However, that resist... 00:18:47.294 --> 00:18:50.263 However, that resistor is a two… 00:18:50.263 --> 00:18:51.140 however, 00:18:51.140 --> 00:18:52.404 maaahhhh 00:18:53.372 --> 00:18:55.069 What I think is most…. 00:18:55.069 --> 00:18:56.396 What I… [clears throat] 00:18:56.396 --> 00:18:57.855 What I think is ppppbbblb 00:18:59.026 --> 00:19:02.197 All it takes is to turn that… haaaaaaa 00:19:03.728 --> 00:19:07.111 What's going on inside these things is weirder than you thought, huh? 00:19:07.111 --> 00:19:09.672 Just like the title said. 00:19:09.672 --> 00:19:14.671 I didn't really know how they work, but when I realized the light would turn on the heater, it clicked. 00:19:15.617 --> 00:19:19.391 Both conceptually, and because the switch opened.