The first step is to get power into the car. You will need either trucks that can bring the power into the car, or "wipers" that pick up power from the axles. Generally, one truck will pick up power from one rail. This only gives you 2 or maybe 3 wheels providing power from each rail, so flickering of the lights is common.
Since you mentioned decoders, I assume you're running DCC. That means that you'll always have power. You will have 14-16 volts of modulated square wave (the DCC "waveform") available at all times. This will work perfectly well to drive an incandescent bulb, or several. You probably want at least an 18-volt bulb, because it will last a lot longer if it's run below its rated voltage. Or, you can use LEDs. LEDs require resistors to limit the current. I use a 1K resistor, and it works fine.
LEDs work on DC, but the D in LED stands for Diode, a device which limits current flow through the device to one direction. So, the DCC waveform will light a LED, although it will only be ON for about half the cycle. You don't need a diode bridge to rectify the waveform. The LED will do that for you. (In theory, it may be better to use a bridge rectifier to "protect" the LED from constant switching, but I have had no problems with connecting a LED+resistor set directly across the DCC rails.)
Incandescent bulbs put out light in all directions, while LEDs put out a "beam," mostly in one direction. To use LEDs, therefore, you need a bunch of them to get even lighting, or some sort of reflective baffle system. Lighting kits which are sold for passenger cars typically have a number of small leds mounted on a strip to accomplish this. LEDs are more efficient than incandescent bulbs, so if you are running a lot of passenger cars, that's probably the way to go. For just a few, you can get away with incandescents.
Several companies make "lights-only" decoders. These are designed for this sort of application, but they're kind of pricey for what they do. If you have an old decoder with a burned-out motor function, you can still use the lighting functions on it. Or, you can get a low-end motor-and-headlights decoder and use just the headlight part. To program these, you'll need to put a resistor across the track to fool the programmer into thinking there's a motor.
You might want to give some thought to the decoder idea, though. It's going to be expensive to equip a fleet of passenger cars with decoders. A small slide switch on the base of the car will do the same job for much less money. Or, you can wire a siding on your layout with a shut-off toggle and store the cars there when not in use.
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Dave
Lackawanna Route of the Phoebe Snow
So, the question to ask is, "How long do the batteries last in normal use?"
Also, "Are these normal batteries (AAA?) or are they really expensive photo batteries that are obsolete after 6 months and unavailable after a year?"
On the plus side, you don't need axle wipers, which saves that cost, and that also reduces the rolling friction so you can pull more cars.
The Rapido light kits run on regular watch batteries.
I don't know how long they last, but with the small current draw of LED's, I expect them to last a while.
The Kid has a caboose with a blinking LED on it. We haven't changed the AAA battery in almost 10 years!
Rotor
Jake: How often does the train go by? Elwood: So often you won't even notice ...
Rotorranch wrote: The Kid has a caboose with a blinking LED on it. We haven't changed the AAA battery in almost 10 years! Rotor
I have a caboose that's been blinking for 16 years, also a triple A Duracell.
Jay
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modelmaker51 wrote: Rotorranch wrote: The Kid has a caboose with a blinking LED on it. We haven't changed the AAA battery in almost 10 years! RotorI have a caboose that's been blinking for 16 years, also a triple A Duracell.
I'm tempted to change the battery in The Kid's caboose just so it won't leak!
If I do, I need to add "glass" in the windows while I'm in there.
Rapido light bars have two LEDs; one at each end. Batteries last only a few hours, but unless you're running in total darkness you won't need the lights on because you can't even see them in normal room lighting. You receive a magnetic wand to turn the lights on and off, which you have to wave over one end of the car to trigger a magnetic reed switch. It's very easy to forget to turn the lights off and drain the batteries. When you do you have to open up the cars to change batteries, but there's no flicker because you're not using track power at all.
Depending on where you purchase the batteries, you can easily spend $10-$20 a week if you use the lights a lot.