Hello, today we are in my living room next to the Christmas tree because I am going to do a little more advanced video about the electrical properties of midget Christmas lights like these. Now many of us know that these lights operate with all the bulbs in series, so the line voltage, 120 volts here in the United States, is divided equally among all the bulbs in the string. We'll take a look at that, but there's more to it than just taking the voltage divided by the number of bulbs because different sets operate at different currents, different amperages. And that's important if you go changing bulbs between different sets or if you save one set for spears or if you're buying replacement bulbs, it's important to know not just the voltage of the bulb but also what current they're designed to operate at. So in this video we're going to take a look at different string voltages and also different currents. We'll measure the current of different strings and I'll also show you how to measure the voltage in current of individual bulbs. First of all, I mentioned that these lights are wired in series. That means that if this is the plug and these are the light bulbs in the string, the light bulbs are connected one after another. So the voltage, when you plug this light set into the wall, the voltage has to go through each bulb in series before going back out to the wall. In C7 and C9 lights, the bulbs are wired in parallel so each bulb would be right across the AC line. With this series set up, if you remove one bulb, the whole string stops working because the current has to flow through each bulb. If there's a break any place in the circuit, if you take one of these bulbs out, the lights all go out. Now the reason that a burned out bulb doesn't make the rest of the lights go out is there's little shunts inside of these bulbs that will complete the circuit even if the filament burns out, or at least they're supposed to. It doesn't always work but that's a subject for a different video. Now two terms are important to understand. This is basic electronics but it's good to review it here. The voltage is the pressure, the force of the electrons forcing electricity through the lights through the set. Current is a measurement of that flow through the set. If you plug this set into the wall in North America, your wall outlet is right around 120 volts. It can vary a little bit but let's say it's 120 volts. That's the pressure behind those lights. Once the lights are working, the glow and current will flow through the set. So again, current is that flow through the lights and you can measure that current at any point along this string and it will be the same. So we're going to measure some lights in a moment and one set will be about 18 milliamps. Current is measured in amperes or amps for short. So you can measure that current at any point in this set. We're going to measure it right here at the plug. But still that current is equal through every bulb. Now because these bulbs are wired in series, you take the available voltage, let's say it's 120 volts, and you divide it equally among all of the bulbs in the set, assuming that every bulb is identical in its characteristics. If you take 120 volts, divide it by a light set with 50 lights that gives 2.4 volts per bulb. We'll round it off to 2.5 for our purposes today. Or if you have a set of 35 lights, that same voltage divided among 35 bulbs is 3.43 volts or we'll say 3.5. Likewise, a set of 20 lights will be 6 volts per bulb and a set of 10 lights, like you might find in a tree tapper, will be 12 volts per bulb, basic math. And for most people, that's the end of the story, but there's more to it. It's important to consider the amount of current that flows through the set if you go to change bulbs. So here I have two sets of miniature Christmas lights. Each set has 35 lamps. And I'm using this device here called a kilowatt to measure the current through each set. These are pretty handy devices for measuring how much power a device uses. You can measure voltage, which here is 121.8 volts at the moment. You can measure the amperage, which is current, or the wattage, which is voltage times amperage. So for the first set, I'll connect this 35 light set. You can see they're all on. And it is drawing 0.18 amperes. Now I'll connect the second set and see how much it draws. This set of 35, again they're all working, only draws 0.12 amps. Now in both cases, each bulb is getting about 3.5 volts because they're 35 light sets. So basic math, 120 lights, excuse me, 120 volts divided by 35 is 3.5 volts per light. But if I take a bulb out of this set and I take a bulb out of this set, they're both 3.5 volt bulbs. They should be interchangeable, right? Let's try it. So I'll take the bulb from the first set, plug it into the second set, and look how dim it is compared to the others. Maybe it's hard to tell on camera, but I think you can see how much dimmer this bulb is. Even though it is a 3.5 volt bulb. So even though those are both 3.5 volt bulbs, they draw different amounts of current when they're operating. So at 3.5 volts, the bulb on the left would draw 18 milliamps. A bulb from the set on the right would only draw 0.12 milliamps. This is important, again, if you're going to replace burned out bulbs or if you're going to take a set of lights and keep the bulbs as spare. Or even if you're going to buy replacement bulbs, you have to make sure that you're not only by bulbs that are the correct voltage, but also the correct amperage. Now, in my case, I don't buy packs of replacement bulbs. I just buy an extra set and use that as spares. So when I save the bulbs out of a set, or if I save the bulbs out of a broken or a damaged set, I have to be careful to keep those bulbs separated by voltage and by current. Now let's look at the characteristics of an individual bulb from each one of those sets. First, here's my test setup. On the left is a variable power supply. This can produce between 0 and 12 volts alternating current or direct current. Incandescent bulbs don't care whether you use AC or DC. For this test, we're using alternating current, just like the bulbs would get in a set, but the same results would be true if we were using direct current. This meter here is measuring the voltage across the bulb, and this meter on the right is measuring the current through the bulb. I have the variable power supply set to just about 3.5 volts close enough for our purposes, and you can see that there is 183 milliamps flowing through that bulb. That's the same as 0.183 amps, as we saw on the kilowatt meter. So we have the same results. 3.5 volts across the bulb, just like it would be in the set, 180 milliamps or 0.18 amps through the bulb. This is a bulb from the set on the left that you saw earlier. Now let's try a bulb from the set on the right. This is also a 35 light set. 3.5 volts across the bulb. I'm going to remove it from its base just to make it a little easier to access the wires. I'll take this little mini-grubber and hook on to each wire, if I can. And we'll turn it up to 3.5 volts. Right above there, and you can see on our current meter running about 0.12 amps, 122 milliamps, same difference. This is a good test setup as well. If you have a bunch of spare bulbs that you don't know what they fit, you don't know what voltage or amperage they are, you can use this setup to adjust the voltage until the bulb looks about right as far as brightness. Then you can see what voltage is operating at and what current it's operating at. Then you'll know as characteristics when you put it in stock to use later. I hope you found this video interesting. When I was researching the characteristics of miniature lamps in Christmas lights, I really couldn't find much online as far as specifications or any other videos that really explained this concept. It took me quite a while to figure out why bulbs at the same voltage wouldn't be compatible in different sets, wouldn't be interchangeable. I finally realized it's because of the different currents in the bulbs. So that's all for now. Thank you for watching. You