Lighting Crash Course

Discussion in 'FAQs' started by FrankG, Jan 13, 2006.

  1. FrankG

    FrankG Member

    I keep asking lighting questions, but I'm just not getting it. Maybe someone can answer some pretty basic questions....

    I'm using miniature bulbs that light at 1.5v (using a battery). They also work at 3v, but are very bright. I'm sticking with the 1.5 because it looks better and hopefully will extend the life of the bulbs.

    What I'm trying to figure out is how exactly this works when there are multiple lights in a structure, and obviously multiple structures on a layout. Here's what I mean...

    I have one structure now that I'd like to put 4 of these lights in. I would imagine that would add up to 6v.

    Let's say I add 2 more structures -- one totally 4.5v and another totaling 7.5v. I'm assuming I would wire them all together for a total of 18v.

    Working with this model, I'd have to increase the power any time I added more lights. Potentially, I could end up with some weird number, like 41v or something. Is that right? Doesn't sound right.

    Or is there some other way to wire this so that each structure only needs a total of 1.5v since the highest voltage for a single light is only 1.5v.

    If this latter option is right, and each structure stays at 1.5v, then what about when I combine the multiple structure? Does it still stay 1.5 or does that become 1.5 + 1.5 + 1.5, etc?

    Whichever option is right...can you tell me if that's parallel or serial wiring so I can look up even more info? Just trying to do this right the first time and plan ahead.
  2. jim currie

    jim currie Active Member

    wire all the lights in parallel you will need 1.5 V if you do 4 in series in each building you would need 6 V then put all the buildings in parallel then each building will need 6V.
  3. nachoman

    nachoman Guest

    it is easiest to find a suitable power supply, then design your circuits to suit. For example, if you use an old cheapie 12v power pack as a power supply, you can use a bunch of 12v bulbs wired in parallel. If you want to use 1.5v bulbs, you will need to wire the bulbs in 8 bulb series circuits (to total 12v). Remember, if bulbs are wired in series and one burns out, they all go out.

  4. shortliner

    shortliner Member

    Why not use LED's? - no heat and extreemly long life
    Shortliner(Jack)away up here in the Highlands
  5. ezdays

    ezdays Out AZ way


    When wiring bulbs in series, the voltage drops add up, when in parallel, they remain constant. One thing, I would not mix different types and voltages of bulbs, even in series, but you cannot in parallel. Let me tell you why. In series, true, the voltages add up, but different bulbs rated with the same voltage may have different current requirements. Since in a series circuit, all bulbs will draw the same current, it is possible that the actual voltage drops across each bulb will be different than you expect. This could result in brigher than rated in some bulbs, and dimmer in others. As you point out, putting more voltage across a bulb will make it brighter, but will shorten its life, sometimes measured in seconds. You obviously can't put bulbs with different voltage ratings in parallel since it's the voltage that remains constant and you have too much or too little voltage across some bulbs causing the same problems.

    You can series the same type of bulbs if you wish, but as Kevin points out, if one burns out, they all go out.

    You could use LEDs, but white and blue ones are considerably more expensive than bulbs, but they require less current and you can wire them in series or parallel, just as long as you are able to calculate the current and add a current limiting resistor to the circuit.

    I hope this helps with your questions. Keep us posted on what you wind up doing.
  6. FrankG

    FrankG Member

    I've been steering away from LEDs because I just don't think they have the same look as incandescent. And I have a BOX of these little tiny (grain of wheat, maybe) bulbs that someone gave I might as well use them. I think they look really I was just trying to figure the wiring out.

    Since you guys are saying that the series draw-back is the one-goes-out-they-all-go-out problem....what are the thoughts in wiring everything in parallel? Pros/cons?
  7. jim currie

    jim currie Active Member

    the only led's that look like incandescent's are called warm whites and my o my are they pricey:(. my thoughts are to go with parallel then if one goes out then you know which one it is also if the bulbs are rated for 1.5V i would run then at 1.3 to make them last longer.
  8. cidchase

    cidchase Active Member

    Hi Frank,

    You would probably like to get away from the batteries.
    You can use a power pack AC output, a DC power supply, or
    even a larger 6v or 12 battery if desired.

    This dwg shows strings of series-connected bulbs. The strings are then
    connected in parallel. The bulb voltage ratings, or voltage drops, in each string
    must add up to the power supply voltage. The bulbs in each string must
    be the same rating, but you can use a different type of bulb in a
    different string. Each string can have its own separate ON/OFF switch.

    You can have fewer or more branches up to the current capacity or VA rating of the power supply.

    If using a larger battery or larger DC power supply, the thing to watch out for
    is the size of the bus or supply wires (too small wire will overheat) and ensuring
    some kind of short circuit protection, like a fuse in the main wire to the

    This way you can have a single source for your lighting power. You can
    also use LED's in the circuit if you want.

    Attached Files:

  9. ezdays

    ezdays Out AZ way

    The big drawback to that is that you will need a series resistor for each lamp that requires less than the power source voltage. That's going to eat up a lot of power, especially those 1.5 volt ones.

    The diagram that Cid has there is worth considering, he's got all the same voltage lamps in the same leg of the circuit. Just be sure that each lamp in the individual legs are the same type, or are rated for the same voltage and current draw. Just as an example, if you had four 3 volt lamps in series, and one was rated at 100 mA and the other three at 50 mA, the 100 mA one would probably burn dimmer and the other three brighter than the bulbs are designed for. I could calculate the current, but suffice to say, brighter than designed for is not better, as I pointed out in an earlier post.
  10. Russ Bellinis

    Russ Bellinis Active Member

    I once got a "universal" transformer for powering battery powered gadgets from Radio Shack. If I remember correctly it had a slide switch that could be set to 1.5 v, 3 v, 6v, or 12v. I don't know if they are stilll available or if they would handle the load without needing one per lamp, but they might be a solution to your problem.
  11. ezdays

    ezdays Out AZ way


    That's another possibility. The closer you get to matching the source voltage to the voltage of your lamp, the less power you waste in adding voltage-dropping, or current-limiting resistors. They just eat up power and turn it into heat.

    One thing that I designed when we had our company were graphic annunciators for security systems. Some of them used literally hundreds of LEDs. I used the technique that Cid diagramed whenever I could, even with LEDs. If I had to light a string of lights, I'd wire them in series. I could light six LEDs in series without a dropping resistor. If I did them in parallel, six LEDs would take about 120 mA and six resistors. In series the same six took 20 mA and maybe one resistor.

    Right now, if I have a choice, I'll use LEDs over incandecent mainly because of the current requirments and the reliability.
  12. 60103

    60103 Pooh Bah

    If you are going to string the lamps in series, try to put an extra lamp or two in so that they run under the rated voltage. For a 12V supply, 8 1.5V lamps is 12V, but 10 lamps would run at 1.2V, slightly dimmer but longer life.
    Remember that you don't get light for nothing. The wattage (VxA) will add up the same. 20ma times 1.5V times number of LEDs. (.03 amps per LED).
  13. GeorgeHO

    GeorgeHO Member

    You have some questions about parallel and series that seem to linger in your mind because there is something you don't fully understand. Maybe I can help.

    Pretend you have a big dam holding back a lot of water (12 volts worth). The dam has floodgates that you can open, but when you do you need something to eat the water or the river will overflow and kill all the people. To eat the water you have these devices called lamps that will eat 1.5 volts worth of water. You open floodgate A and attach 8 lamps to it (in series) and they eat all the water (1.5x8). You open floodgate B and attach 10 lamps to it and they eat all the water (1.2x10). You open floodgate C and attach 4 lamps to it and another device (resistor) which eats as much water as the 4 lamps. This too eats all the water, but the water used by the resistor is TOTALLY wasted. That water does not do anything but stop the lamps from exploding (too much water means wearing out too soon, or burning out).

    Floodgates A, B, and C are connected in parallel. You can open as many floodgates as you want, but eventually the number of floodgates will exceed the capacity of the dam, and the water level (voltage) will drop, or the dam will become empty.

    The lamps (and resistors) connected to any specific floodgate are connected in series. Connecting more lamps to one floodgate means they will share the 12 volts available to them, 120 lamps in series would each consume .01 volt.

    I hope that helps

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