Night and day on the WR&N IV

The day-night lighting system I built for the WR&N IV, dubbed "The Time Machine," was a hybrid of high- and low-tech. Three standard wall dimmers were driven by Hankscraft very-low-RPM motors to slowly fade white (daylight), red (sunset) and blue (twilight) banks of lights. Microswitches were used to limit the range of motion and to cascade the activation from one bank to the next. Motor speed was adjustable to change the rate at which the day-night-day cycle proceeded; at the slowest setting it was hard to know when the cycle was complete, so I added an LED indicator. The circuit is shown below. (Not included in the diagram are the dimmers.)

For daylight illumination I used high-intensity halogen lights for their compactness and good color temperature. A string of Christmas tree lights was used to simulate a sunset, with yellow, orange, red and purple bulbs arranged to grade the color from a bright central spot out to the sides. Then, for the twilight effect, several strings of all-blue lights ran the full perimeter of the layout, with additional strings overhead.

During "daylight" all lights were on—the white lights simply washed out the glow of the reds and blues. Then, as the whites dimmed, the reds became more visible, creating the illusion the sun was setting. As the reds dimmed, the blues became more visible, simulating the onset of twilight. Finally the blues would dim out for deep night, when the layout lighting would rise to full effect.

By the way, standard light dimmers ordinarily created an unwanted effect when coming up from total darkness: the lights would not gradually brighten, but suddenly "pop" when the dimmers are at about 30% brightness. To solve this problem, I adjusted the limit switches to prevent the dimmers from being turned completely off. By leaving the bulbs powered at a level where they were too dark to see under normal conditions, they would fade up smoothly without the pop effect.

Building, vehicle and street lights were turned on and off in a pseudo-random sequence using a bank of photodetectors that activated magnetic reed-type micro-relays. The photodetectors simply responded to changes in room brightness. The circuit was electrically independent from both the lights it controlled as well as the day-night lighting system (relays allowed me to use different voltage supplies for the lights, and reed relays are silent).

The photo above shows the photodetector assembly, which has twenty circuits. The objects in the top row are photoresistors; objects in the second row are potentiometers, which allow me to tweak the on-off-time of each circuit if I want. Next are the driver components that energize the reed relays, which are the rectangles in the bottom row. The breadboard was mounted on the fascia at one end of the layout, right out in plain view, so reflections and shadows of people moving around the room altered its behavior; plus, it made for an interesting conversation piece.

Future Plans

When I get to build my next permanent layout, I will use a very similar system with just one minor variation: I will have a different bank of lights for a sunrise effect, so that the sun won't be rising and setting in the same place. It's a simple matter to direct the power to the appropriate light string using the rise/set control switch. Also, the sunrise lights would have subtly different colors than the sunset lights. As for model lighting control, I cannot think of any reason not to re-use the controller shown in the photo above.

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