Layout lighting is powered with a low-voltage transformer. Lights are connected to a transformer with wiring. Lights are controlled via connections through electrical switches and/or the relay contacts of Three-Rail Innovations' 2LR or 2RC controllers.

This section starts with very basic lighting and wiring concepts, then proceeds with relay connections for turning lights on or off when a relay is on, selecting a light to be on, and connections for parallel and series operation of lighting.

The light holder (to right) is used to represent any of the many available layout lighting accessories. Two screw terminals are used to attach wires for powering the lights. Layout lighting accessories may have screw posts or wire clips. Often, one wire connects to the metal structure of the accessory; it is best if accessories cannot touch each other or track.

The example light holder appearing in following diagrams may actually be any single layout light, an accessory with multiple lights, or a string of lights wired together, shown to left. Any number of lights or lighting accessories can be connected in the "parallel" manner shown, and powered together, limited only be transformer power and any switches or relays used for control.

Layout lighting is powered by one or more transformers. Transformer voltage is selected to accommodate light bulbs in the accessories or whatever is being controlled.

More than one transformer can be used for layout lighting, to accommodate different voltage bulbs, to connect more bulbs than a single transformer will handle, or to provide adjustable brightness for some lights.

Transformers are available the have multiple voltage taps. These are well suited to powering layout lighting that uses different voltage bulbs or to provide different light intensities.

Lights are powered by connecting one wire terminal on the light to a post on the lighting transformer, and the other light terminal to the other transformer post. The light will be on whenever the transformer is powered.

Connections are similar when more than one lighting transformer is used. One terminal of each lighting fixture is connected to the "lighting common" transformer posts. The other light terminals are connected to transformer posts appropriate for voltage or desired brightness.

Electrical switches are used to turn layout lighting on and off. There are many types of electrical switches and most can be used to control layout lighting. Following diagrams use two types of electrical switches: SPST (Single-Position-Single-Throw) and SPDT (Single-Position-Double-Throw), illustrated to right.

• An SPST switch has two wire connections and is suitable for turning one or more lights ON and OFF.
• An SPDT switch has three wire connections and can be used for selecting a group of lights that will be ON or selecting transformer voltage level for lights.

A SPST switch can be wired to turn layout lighting OFF and ON.

A SPDT switch can be wired to select one of two groups of lights to be ON.

A SPDT switch can also be used to select from two power sources for a light.

Switches can also be wired so a light is controlled by two switches.

Say, for example, switch 1 represents "Day" or "Night" on the train layout:

• When "Day" is selected, light B is ON, perhaps lights in the stores on main street. Lights A and C are always OFF.
• When "Night" is selected, light B is OFF and light C is ON (street lights), but light A, the lights in houses, is turned ON and OFF with switch 2.

Turning layout lighting OFF and ON adds action and enhances visitor appeal. Problem, though, is that the switches have to be thrown, distracting the operator from running the trains! Also, there is a practical limit to the number of switches and switch combinations, and switching activity, that an operator can easily manage.

Relays are switches that can be "thrown" electrically. The relays used on Three-Rail Innovations' controller products correspond to SPDT switches. Diagrams show screw terminals for wire connections: NC, for "normally closed," C for "common," and NO for "normally open." The relay switch contacts and connections are illustrated for relay "OFF" and "ON" conditions.

When a relay is OFF, there is a connection between the NC, "normally closed," and C, "common," terminals. There is no connection to the NO, "normally open," terminal.

When a relay is ON, there is a connection between the NO "normally open," and C "common," terminals. There is no connection to the NC, "normally closed," terminal.

Three-Rail Innovations' relay control products throw relays when trains are in particular track blocks, for specified times, repetitively in time cycles, by counts of trains passing a track section, by days-of-the-week, or many other ways. Any controller "features" can be used to automatically control layout lighting.

The following simplified diagrams show only the relay "switch" terminals; the wiring techniques illustrated are independent of the controller feature selected and controller activation techniques. Refer to specific Three-Rail Innovations' product descriptions and applications for complete lighting examples.

Relays can be wired to turn lights off and on, select one of two lights to be on, select light brightness, or operate lighting in combinations of multiple relays.

A Light can be turned OFF or ON when a relay is ON.

A relay is used to select either Light-A or Light-B to be ON.

Light-A is ON whenever the Relay is OFF, OFF when the Relay is ON.

Light-B is ON whenever the Relay is ON, OFF when the Relay is OFF.

One relay turns a light OFF or ON and another is used to select "bright" or "dim."

The light is On when Relay-2 is ON. It is "bright" when Relay-1 is OFF, "dim" when Relay-2 is ON.

Lights can be turned off and on with combinations of relay actions. Multiple relay contacts can be connected in parallel or series to turn a light ON.

Light ON when Parallel relay contacts are closed.

Light-B is wired to the Relay-2 NO terminal, and is ON when Relay-2 is ON.

Light-C is wired to the Relay-1 NC terminal, and is ON when Relay-1 is OFF.

Light ON when Series relay contacts are closed.

Light-B is wired to the Relay-1 NC terminal and the Relay-2 NO terminal. It is ON when Relay-1 is OFF AND Relay-2 is ON, otherwise OFF.

Light-C is wired to the Relay-1 NC terminal and a transformer post. terminal. It is ON when Relay-1 is OFF.

Click a lighting topic to see how these wiring techniques can be used to add lighting action to your train layout.