LEDs (light emitting diodes) are very usefull in all types of modelling where you want to install lights. They draw very little current, give off no heat, have a very long life and come in a variety of sizes, colours and shapes. However their light output is very directional and they often require dropping resistors in the circuit.
For a locomotive or car headlight you can use two types of leds. One is the prototype white led that has a golden glow like the older style globe type headlight, the other is the daylight white led that is a pure white like the modern haleogen globe type headlight.
Round or rectangular red leds can be used for tail lights and marker lights
Led connections and resistors
Leds need only 2-3 volts to get them to light, so a dropping resister is needed in the circuit other wise they go kaput and we sell you another one. I have checked a few leds along the way to make sure they go kaput, and they do! We can supply the correct resistor, often 1000 ohms with our leds to make sure they work..
These leds have two legs or connections that are wired in the lighting circuit. The longer leg is called the Annode and the shorter leg is the Cathode. You can trim these legs to size to help them fit. The resistor connects to the ANNODE.
Leds are polarity sensitive which means they will only work when each leg is wired to the correct polarity. Wire the annode to the POSITIVE side and the cathode to the NEGATIVE side of the circuit.
With DCC decoders this means the BLUE wire (common or +ve ) to the resistor and the YELLOW or WHITE or GREEN to the cathode (-ve).
The picture shows an inexpensive battery powered led tester (18187). You use it to determine the correct way the led is to be wired and if an led is still working or kaput..