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Lighting types and sources can be mixed and matched in any combination...to a point. It is generally considered unwise at the very least,
and
dangerous at most to connect different types of lighting in the same circuit. Don't try to jump from an LED to an incandescent to an LED just because it will save you from having to run more wires. If you're lucky, the circuit will simply short out. Worst case scenario is your mom/wife/girlfriend comes home and finds you standing in a pile of ashes that used to be your house with a glob of melted plastic in one hand and a pile of wires and bulbs in the other trying to figure out what went wrong!!!!
Safety disclaimer aside, on with the lesson...
You have to keep track of the distribution of voltage (how "much" power is going to a given light source) versus amperage (how
"fast" it is getting there). Part of the balance of voltage vs. amperage lies in how a given set of lights are to be connected. Circuits can be wired one of 2 ways, serial or parallel.
Serial wiring increases the amount of voltage needed to run a circuit, while amperage is generally unaffected.
Parallel is the reverse, voltage remains constant while more amperage is required.
Physically, the two circuits look something like this:
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Serial circuits are like cheap Christmas tree lights ("One goes out, they ALL go out!!!"). The two connections on the bulb, positive and negative, are alternately connected to each other in sequence... positive of bulb 1 to negative of bulb 2, positive of bulb 2 to negative of bulb 3, positive of bulb 3 to negative of bulb 4, and so on until you get back to the power source and switch. If one bulb burns out or is removed, it breaks the chain and all other bulbs go out. Most models are not lit this way. Exceptions may be things like running lights, where you want them all to blink at the same time (We'll get into blinking circuits later on.)
Parallel circuits are like the good Christmas tree lights...take out one bulb, the rest remain lit. In parallel circuits, the positives from all bulbs are connected to the positive of the power source, and likewise negatives to negative. Each bulb has its own connection to the power source, independent of any other bulb in the circuit. If one bulb burns out, the others are unaffected (almost).
Serial vs. Parallel is also where voltage vs. amperage comes into play. A bulb has both ratings on it, X amount of volts at Y amount of amps. Let's say you are putting 4 bulbs in a model. Each bulb requires
3 volts at 10 amps (very large bulbs by lighting standards, but it makes the math easy to follow for the sake of this example).
In a serial circuit, voltage increases as you connect the bulbs so, (4) 3 volt
bulbs at 10 amps each will require a power source that provides 12 volts at 10 amps. (4 x 3 = 12, amperage rides through the circuit back to the power source).
The same 4 bulbs connected in parallel would
require a power source of 3 volts at 40 amps (4 x 10 = 40, voltage rides through the circuit back to the power source).
Voltage and amperage ratings on bulbs and power sources are not exact, they are the
average that that device can handle/deliver. There is about a 10% variance in each direction. A 12 volt/1 amp power source might fluctuate anywhere from 10.8 to 13.2 volts at .9 to 1.1 amps. A 3 volt/.5 (half)
amp bulb might be able to handle from 2.7 to 3.3 volts at .45 to .55 amps. When designing lighting circuits, try to allow for this variance on both sides (bulbs and power source) of the circuit.
Which type of circuit is better? For our purposes, neither is more advantageous from an energy efficiency point of view. The voltages and amperages we are dealing with are minuscule compared to the amount of electricity required to run your computer or stereo. Lower values are obviously better, from both a power efficiency and basic safety point of view, but don't lose any sleep over it if you have to use more batteries or a larger power adapter. The point is you have to keep track of what you are connecting and how they affect each other. Before you do any sort of work drilling holes or cutting parts on a kit, plan out your lighting circuit on paper first. Make notes of voltages, amperages, positives and negatives. I find that sometimes it helps to make my notes on a copy of the instruction sheet. That way, I can see how wiring paths look in 3 dimensions, by drawing "right on the parts", so to speak.
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