Wiring lights: Connecting light fixtures to a power source.
A light fixture is an electrical device which connects to a circuit in order to power an electric lamp such as an incandescent bulb. Understand that incandescent means something which emits light as a result of being heated. Luminescent refers to light that is not emitted from a form of heat and thus does not necessarily require electricity. Here we are dealing with electric lamps which are held in place and supplied electric current through a device called a fixture. Other types of fixtures and devices can be powered in similar fashion, and this article presupposes that you are dealing with prefabricated fixtures and established electrical circuitry, like what you would find already constructed into buildings or even in a car or computer.
To get started, it’s always good to be knowledgeable about the basics of working with electrical wire, because wire transmitting electricity is what you will be dealing with here. Furthermore, consider that many regions have strict building and electrical codes and regulations which are enforced by law. In some cases if you are altering the physical makeup or circuitry within any structure, you may be required to have inspections and certifications before and/or after any changes are made. That being said, this process can also be replicated on a table with a battery with a couple pieces of wire and a light bulb (electric lamp).
Electric lamps can vary greatly in operation, but they all generally function the same by converting electric current into light. As mentioned, incandescent light is produced from the heating of materials using electricity (the process seen in incandescent lamps/bulbs), while gas discharge light is produced as a result of sending electricity through an ionized gas (as seen in fluorescent and neon lamps). Arc lamps are a type of gas discharge lamp which produce light by creating an electric arc between carbon electrodes in the air; rather than using ionized gas as a conductor that illuminates the current’s path, an electric arc occurs when the gas air between an anode and cathode is physically broken down into plasma by electric current which makes a brilliant jump between the electrodes and burns its way through the air.
Alternately there are also lamps which utilize special materials in diodes, which are ready to emit light as soon as they become activated. Again, think back to batteries and transmitting electricity through wire; energy is being transferred as electrons jump between atoms. In the case of these special diodes, think of the material they are made from as containing atoms which are only partially complete (lacking electrodes). Only when electrons have been added (passing through the diode) will the atoms reactivate and comes back to life emitting light in their natural form. This is a kind of lamp referred to as a light-emitting diode, more commonly known as a LED.
All of these examples of lamps generally function the same in that they generate light by allowing electric current to pass through them; a positive line to deliver the power in, and a negative line to pull the power away. Different electric lamps require different amounts of electric current based on their construction and how much light they are used to emit. The fixtures for these various lamps and bulbs not only hold the device in place and deliver current to it, they can also physically protect the lamp, regulate current going to it, focus the direction of light or be adapted to serve various other functions.
Commonly, fixtures are manufactured to work with specific light bulbs and electric lamps. They will clearly indicate what amount of electric current is required for their recommended operation. As a rule of thumb, disconnect your circuit from its power supply before working on any fixtures or devices that are connected. If you need to know the amount of power running through your circuit first, be safe and use a voltage tester at a socket or fixture before you disconnect power.
As diverse as they can be, fixtures will commonly have a few of the same features between them, since they operate the same way; they require that good old line in, the line out and possibly need to be grounded as well. As such, fixtures will have terminals to attach all these wires to, often with color-coated wires already attached to make connection easier. If you read up on the basics of wire, don’t forget that different regions use different colors to indicate wire purpose, so if you are digging into a building make sure to get familiarized with what your local white wire might mean instead of a green wire or black wire. For a generalized reference point, check our wire color guide here.
From here, assuming that you disconnected your power source and taken any other precautions, you will be adding a fixture somewhere along the line of your electrical circuit. This may require a splice or junction, but it can really be as simple (in theory) as connecting the positive wires to positive wires, negative wires to negative wires, and grounding wires to grounding wires or simply another piece of metal that can be grounded. Some fixtures and devices can be operated on current flowing through no matter if one end is positive and one end is negative; so long as the current is properly flowing through it will operate. Check to be sure with the fixtures or devices you are using.
If replacing a fixture with another fixture, just disconnect the old fixture and connect the new one the exact same way. Wires will be connected together with wiring caps. Remember that all wire usually is anyway, is twisted metal strands, so twisting the ends of wire together connects them and extends their conductive range or connects them to devices. Exposed wire tips twisted together can then be screwed into wiring caps, which help protect and insulate the exposed wire. Consider this when you are disconnecting old fixtures or having to add new ones.
Common circuitry will have positive and negative wires transmitting electric current in a loop between the positive and negative terminals of a power grid or battery. If you are adding new devices or fixtures, just make sure that you are keeping this circuit intact and that the integrity of this loop is maintained. Once electricity is turned back on and flowing through the circuit, if it doesn’t have a set course to get back it is going to find another and discharge into something (or someone) nearby that you weren’t intending it to do.
A fixture can additionally function as the junction where electric current is redirected back to the negative power terminal or cathode of a battery.
If you are simply take a disposable battery (the power supply), and attach a wire from the positive end (anode terminal) to the positive line on a light fixture, nothing will happen, as the electric current has nowhere to be pulled towards and the circuit cannot be completed. As soon as you attach a second wire (or any conductor) to connect the negative line of the fixture to the negative end of the battery (cathode terminal), the circuit will complete, electric current will flow and if the fixture contains an electric lamp it will illuminate. More fixtures can be added in between these positive and negative wires so long as they put back what they take out. More fixtures and devices create more resistance, so any circuit will have a limit to how many devices it will be able to power and how much work the electric current will be able to do (wattage).
Scale everything up to taste and requirement, just play it safe and remember to check what your local regulations are if you are dealing with circuitry that is incorporated in structural buildings or being used to transmit vast amounts of electricity.