Lighting up your model

Let's just say, you have spent hours of research to make your X-Wing or Gundam model as accurate as possible. All the painting schemes and scratchbuilding has been done. Finally, after hours and weeks of work, your model is complete. And it sits proudly on the shelf.

Later on, you and your friends watch flims on TV related to your model. The film is so exciting, you turn your head and look back at your model. It is still siting proudly on the shelf. But then, you realise there is something missing. Your model does not have lights. Now, its just sitting there on the shelf, doing absolutely nothing.

Lights and some degree of movement does help enhance the model in terms of realism. But before you start lighting up you model with matches, bulbs or even fireworks, there are some things to consider:

For example,

Let's say you want to light up your 1/24th scale police car. Plonking a 5mm LED into the headlights is like having a 12cm light bulb in reall life. The closest LED colour you can get for your headlight is either yellow or pure white. And since the LED needs power to light it up, most of the time, you cannot use a battery as it might be too big for the car. The police car has flashing lights and so, you need some electronic circuits to make it flash and again, you are faced with the problem of space inside the model. And where can you put the speakers for the siren? How about accessibility in case the LED or bulb burns out?

These are some of the points to consider for the model before you even start your project. But here, we are going straight to the electronics.

Choice of Lighting

Below are some guidance to help you in deciding which is the best method to light up your model. The table below loosely describes each lighting system (and cannot be used as a Bible of any sort). There are other types of lighting such as bright but fragile CCF (Cold Cathode Fluorescent Tubes) but it will not be discussed here (OK, so I can't easily find them on the market here). Also, Fibre-optic strands are not a source of lighting but helps in distributing dots of lights onto large area where EL or CCF is not available, or when the modeller prefers to use a minimum number of light-source to spread light all over the model due to over-heating concerns.

  Average Size Colour Brightness Pros Cons
Bulb 3mm to 8mm Yellowish white,

12 lumens

Light Radiation at 270º

Has very large light radiation pattern

 

Tends to heat up and also the model within

Average lifetime shortens if bulb is continuously switched on and off

LED 2mm to 10mm Blue, Cyan, Green, Orange, Purple, Red, White, Yellow

28mcd (brightness depends on LED manufacturer)

Light Radiation at 60º to 110º

Has an average lifetime of 10,000 hours

SMT version is small enough for a 2mm x 3mm footprint

Not as bright as incandescent bulbs
Luxeon 20mm x 7.5mm Blue, Cyan, Green, Orange, Purple, Red, Royal-Blue, Red-ORange, White, Yellow

80 lumens

Light Radiation at 110º

Brighter than a normal bulb

Has an average of 80 lumens depending on Luxeon type

Generates a lot of heat if not driven directly, to the point of melting the model from inside

Requires a driver circuit to efficiently drive the Luxeon LED

Electroluminescent (EL) Depends on Design Blue, Blue-Green, Orange, Red, White, Yellow-Green

70-100Cd/m²

Light radiation depends on how you fold/curve/cut/shape the media

Media is paper-like, can be cut to size and bent to suit model's curves

EL Drivers must be made to suit EL size

Depending on size of the model, the EL Driver or inverter would usually end up outside the model

Each lighting system requires a form of power. And depending on how much light-source was used, the power supply changes accordingly. A good example would be to light up 20 x 5mm LEDs which consumes about 400mA. So, you would need a 9volt 500mA Mains Power adaptor (with proper current limiting resistors for each LED, of course) and not a battery as it would exhaust itself in a matter of hours. Personally, where models are concerned, I would use a Mains Power Adaptor whenever I can. This is because, if you forgot to change batteries after some time, they will leak and the chemicals will wreak havoc not only on the electronics but also your beautiful model (unless you intentionally wanted it to be, in the first place)

 

The LED

The LED (Light Emitting Diode) is a semiconductor diode that emits visible light or near infra-red radiation when it is forward biased. In other words, when you connect the LED to the way, it lights up. Inside the LED is a semiconductor which is encased in a transparent epoxy resin which could be either diffused or clear lens. The LED, unlike a normal bulb, has a limited viewing angle between 30º to 90º.

This is the symbol for the LED when used in electronic diagrams

 

The longer leg is anode (positive) and the shorter leg is cathode (negative)

 

Another recognisable feature is the flat edge (on the left) or the bigger electrode where both indicates a cathode (negative) side

 

The light radiation (or viewing angle) for a LED is very narrow. A clear lens would have a narrower viewing angle but is very bright. It will create a miniature spotlight effect. A diffused lens would have a better viewing angle but "glows", which is usually used as indicators.

Some samples of Luxeon Star LEDs on display

Samples of Luxeon Star LEDs being lit

 

Current Limiting Resistor for LEDs

A LED is a current device. Therefore, it must have a resistor in series if you do not want to open up your model to replace a burnt LED all the time. I always use the following formula when calculating the value of the current limiting resistor for the LED.

Resistor = (Voltage supplied - LED Voltage) / LED Current

Example:

You need to light up a LED from a 9volt battery, so, yo must choose the correct resistor to give the correct amount of current.

Resistor = (Voltage supplied - LED Voltage*) / LED Current*

Resistor = (9 - 1.8) / 0.018

Resistor = 400 Ohm

The closest value for this (Under the E12 Resistor value) would be 390 Ohms

* - Different LED colour has different current requirement, which could be from 10mA to 30mA. Luxeons would be from 350mA to 1000mA.

 

How to read a Resistor

Once you calculated the resistor value, it is time to get them. And it is important that you know how to identify each resistor after you have bought them. A resistor can be identified via the 4 colour bands on its body. The first three bands are the resistor's values while the fourth band not only tells you which direction the resistor must be placed for reading, it also tells you its tolerance.

Value Colour Colour Multiplier
0 Black   1
1 Brown   10
2 Red   100
3 Orange   1,000 = 1K
4 Yellow   10,000 = 10K
5 Green   100,000
6 Blue   1,000,000 = 1M
7 Violet   10,000,000 = 10M
8 Grey    
9 White    

 

The resistor above shows the value of 47K Ohm. To read its value, hold the resistor with the Gold/Silver band facing right.

Read off the colours (from left to right) of the first two bands and then multiply with the third band.

i.e.

Band 1 = Yellow = 4

Band 2 = Violet = 7

Band 3= Orange = x1,000 Ohms

Total is 47,000 Ohms or 47K. The Gold band denotes 5% tolerance.

 

A simple LED circuit

Let's say you want to light up your X-Wing fighter's engine ports. As the wings are moulded in one piece, you would have to drill some tiny holes for the 5mm LEDs. You can put a LED (optional) to light up the cockpit by using another LED (yellow or white) with the same resistor values. You might want to increase the resistor value to dim the LED for the cockpit as it is only used to highlight the pilot as if the lights are coming from the dashboard's instruments.

For more accuracy, you would have to put the 5mm LED deeper into the exhaust port and slot in a red trasparent octagonal fin after it. (I am drunk here, is it just babbling)

OK, there are 12 fins in there but I only have time to make eight.

This is the circuit diagram for the X-Wing's engines. To be more accurate, you'd have to source for purple LEDs (they do exist)

 

This is how it looked when you put LEDs into the X-Wing fighter's engine ports. This model belongs to fellow Forummer KooWilliams

 

Tools required

The tools required for installing LEDs into your models are:

1) Soldering Iron

Get a good soldering iron with a sharp pin-like bit, that costs you between RM40 to RM60, I suppose and if possible, made in Japan. And the wattage, 25watts should suffice. Anything higher or lower, you would be burning a lot of things. And while you're at it, get some good solder to go with it, you will need those thin ones (about less than 1mm in diameter) as they will melt faster.

Why is the wattage so important? When you're soldering, you're actually transferring heat from the iron's bit to melt the solder which then sticks to the component/printed circuit board (PCB). So, while you're doing this, the heat from the iron would be lost and it needs time to regenerate. If you do not realise this, you would be touching the soldering iron and the glob of semi-melted solder, waiting for it to melt. And while you're doing that, the heat building up from the soldering iron would be tranferred to the component/PCB (instead of staying on the bit), which in turn, could be bad news. The intense heat could cause the component to fail prematurely or the disintegrates the bonding between the copper tracks and the PCB. And that, folks is the problem with low wattage iron.

Too high a wattage, is like literally using a flamethrower to light a cigarrette. And you'd be buying lots of heat clamps (that transfer heat away from the iron and the component) to prevent from burning up or melting everything.

In the end, when you're soldering, the faster, the better, which I counted is not more than 4 seconds. We'll get to the soldering aspects later on.

 

2) Multimeter

This is one of the most important tool for testing LEDs apart from a LED tester (When I have the time, I'll show you how its done). Using the meter, you can test the LED's polarity and also whether its working or not. One advise when buying a meter is to get an analogue version, and if you wish, you can get (a copykat) one for under RM28. But an original SANWA meter would cost you RM125 or thereabouts and it guarantees absolute peace of mind..

Compared to an Analogue meter, the Digital Meter is only suitable for measuring voltages acurately. Usually, it does not have enough current to allow you to test a LED.

When you're testing the LED, twist the knob ultil it points to the lower right

at the X10 (15mA) position. If you do not want to use the meter, point the

knob to the "OFF" position, OK?

 

Using the meter probes with one hand takes some considerable skills. It is like holding a pair of chopsticks in your hand.

So, after much Chinese take-outs, your chopsticks skills would have improved considerably

 

If you open up the meter, you will see that everything runs from

2x AA batteries. And see the fuse at the bottom right? I usually

remove it and replace it with a piece of wire since it blows

easily when I am not too careful.

 

 

To Be Continued