Lighting can add another dimension to models. It is not too difficult, however, It needs some pre-planning and there are a few issues.
Types of illumination, filament bulbs.
The oldest method is to use grain of rice or grain of wheat bulbs. Grain of rice bulbs are a tiny 2mm x 6.5mm. Grain of wheat bulbs are 3mm x 7mm . They are quite current hungry at 30ma and 50ma each respectively and run at 12V. The four bulbs used in the shops model take close to 100ma in total !
Filament bulbs give a warm yellowish light which simulates gas lighting, if used on a lower voltage. The main problem is reliability and inaccessibility. If one blows they can be impossible to replace in some cases.
LEDs are much more reliable and use less power. White LEDs can be a bit harsh giving a much whiter light than filament bulbs. There are now many sizes from miniscule “chips”, to over 10mm in diameter. The most common size for model buildings is 3mm. You can use yellow LEDs to simulate gas lighting.
The voltage required for LEDs varies depending on the colour. You will need to use a resistor to run them on 12 volts. The voltage needed for full brightness is usually referred to as Forward Voltage or Vf. The current is usually set at 20ma. The table below gives an approximate guide. you can increase the resistance to reduce the brightness.
|Colour||Vf||Resistor required for 12v supply at 20ma( full brightnes)|
|Yellow Green 3mm||1.8||570R|
|Full green 3mm||3.3||470R|
Card buildings are the easiest to light as the card tends to block light. However plastic kits need more attention. Paint the insides of the walls black. You may need to make a light box around shop windows, out of styrene. this will stop any light bleeds. Use filler to address any gaps and test with your choice of lighting, before sealing the building up!
Wiring it up
Filament bulbs usually come pre-wired . These can be threaded through a hole in the building’s base card. You can get LED’s that are pre-wired for 12v. I usually use a dab of UHU to hold them in place, or you can use hot clue.
Make up a power “bus” under the model using doll’s house self adhesive copper strips. Solder the wires from each bulb to the bus bar and then Add the wires that will go to the PSU. If you are using LED’s use red and black wires so you maintain the correct polarity as LED’s only work one way round, Unlike filament bulbs.
Powering the lights
The 12v accessory output on model railway controllers can be used. You can also use the 16v AC output with a resistor for 12v bulbs. LEDs can be used on AC by wiring another diode across the LED and adding a resistor of about 1K, for white LEDs. This gives full wave rectification, experiment with the resistor value.
Old 12v DC controllers can be used to give variable brightness.
An example circuit is shown below using two LEDs, with one reversed. This is for 8V AC, hence the 560R resistor,