Lighting models IV: Installing and using LEDs
Welcome to my article on model lighting! I cover different technologies that are useful for people who want to illuminate scale models of various kinds – cars, ships, dollhouses, etc.
And I don’t mean shining external lights on the model, of course. I’m referring to the technology to make tiny light sources that appear to-scale with the model itself.
To sum up the previous chapters, LEDs are a pretty useful and flexible way to light something up. Whether you’re putting a single diode into a small house on a model railroad, or a whole panoply of computer-controlled Neopixel chips into a model spaceship, you’ve got a lot of choices available to you!
CHAPTER CONTENTS
Wiring up an LED
There really isn’t much to this, to be honest. You simply connect the positive lead or pin from each LED to the positive side of your circuit, and the negative to the other. Any resistors, limiters, or switches must be wired in series (ie: sequentially in the circuit, not parallel or side by side) with the LED.
Multiple LEDs themselves should be wired in parallel to the power source, however. It’s generally a bad idea to wire multiple LEDs in series. Partly because if one fails the whole string fails, like old Christmas lights. But mostly because LEDs, especially if they’re different types, manufacturers, colours, and sizes, have slightly different current draws. So unless you're assiduous about only wiring identical LEDs in a series configuration, you run the risk of your whole circuit conking out in the future.
Of course, that said there are other people who disagree and feel that series wiring of LEDs is just fine so long as the LEDs are rated the same. Personally I don't think it’s worth the risk of hassle, given how infrequently I wire up LEDs. And I’m not doing manufacturing, so I have less control over LED specifications and less concern over circuit costs.
Note that resistors and switches are not polarized - it doesn’t matter which way around they are in a circuit. However both LEDs and current limiters are always polarized - they’ll have an end marked as positive, and must be wired the right way around.
Wires
Wires are not a big deal with LEDs in simple situations. They’re such low current devices that you don’t have worry much about wire capacity or loads or anything. Especially for models where sizes are small and thus wire runs short. However, if you have tons of LEDs and long cable runs then you may need to pay attention to wire thickness to ensure enough power gets to your lights.
Wire types
So basically, with small models, just choose any type of insulated copper wire that’s convenient for your project.
Thin plastic-coated wires.
I normally use the thin wires used for wire-wrapping project boards, though lots of other options exist. For example, if you're on a tight budget, telephone and Ethernet cable contain thin wires inside an insulating sheath. If you have any spare phone or data cable around, open it up and pull out the thin wire within - cheap and good sized!
Wire size in the USA and Canada is measured in AWG (American Wire Gauge) sizing, which is an arbitrary series of sequential numbers used to describe wire diameter. The smaller the number, the thinner the wire. So thin wire wrap material could be AWG 28 or 30. In Europe the cross section area in square millimetres is used, rather than wire diameter or whatever. Which is logical, but results in numbers that are harder to remember. AWG 28 is about 0.081 mm2, and AWG 30 is about 0.051 mm2.
Solid or stranded is another choice that isn’t that important for this application. Solid core wire has a single thick copper wire covered with insulation, and is generally stiffer. Stranded wire is made up of multiple thin strands of copper wire, and is generally more flexible. Either is fine - it’s a matter of what’s more convenient to you.
Since LEDs are polarized devices it makes sense to colour-code your wiring as you install it. Usually positive is red and negative is black, though this is obviously just convenient tradition.
Magnet wire.
Or, if you’re making a super tiny model, you might want the thinnest wire possible. Magnet wire is single-strand coated copper wire used for making transformers, electromagnets, and the like. It can be as thin as a cat’s whisker and, since it’s covered in clear or reddish varnish, is insulated. You simply need to lightly scrape off the varnish where you want electricity to flow. Use the edge of a blade to avoid nicking and damaging the copper. Or just solder - the heat from the iron should burn off the varnish.
I would avoid using magnet wire if you need to carry power to a bunch of devices, or if you have a long distance to cover.
Copper tape.
Copper tape is another way to run low-load wiring through a model such as a doll’s house or railway. You just have two parallel thin self-adhesive copper strips that you stick to convenient surfaces. Small nails driven through the tape let you attach branching wires. The thinness of the material makes the tape very easy to conceal. The drawback is that it's fragile, easily damaged, and not terribly reliable. It also can't carry high current loads.
Conductive paint.
Another approach is to skip wire altogether and use something else. For example, let’s say you have a bunch of lights running up inside a model building or spacecraft. You could have a spaghetti collection of wires, which would be a bulky and confusing mess. Or you could run two parallel brass rods or strips down the middle, and use those as your bus bars or power distribution system. Simply solder each LED or branching wire to the strips.
Or you could even use electrically conductive paint in a few cases. This lets you simply paint your wiring wherever you need it. It’s not remotely efficient, so isn’t appropriate for long distances or for carrying a lot of current. But it’s ideal for difficult situations. For example, SMD LEDs are notoriously difficult to wire up as they have incredibly tiny contacts. So you could run a bit of bare wire up alongside the SMD and simply add a blob of paint to bridge the gap without messing around with solder.
Conductive paint can also be used on the surface of models to create basically invisible wiring that can be carefully painted over. Let’s say you want to put a LED on the end of a very thin rod. You could use a brass rod, and use it as one conductor. Then you could paint it with a thick layer of regular paint, which serves as insulation. Add a second layer of conductive paint over top, and then a final layer of whatever colour you want the thing to be. You’ll get some voltage drop caused by the poor conductivity of the paint, but lighting LEDs for a model isn’t exactly a critical application.
The biggest risks with conductive paint, aside from the voltage drop issue, are that it can't be flexed without cracking, and is much less reliable than soldering. So if you use it somewhere where there are moving or bending parts, expect the connection to fail at some point! It also doesn’t conduct electricity particularly well and so is only really useful for short distances.
Enclosing LEDs
LEDs are generally not particularly demanding when it comes to installation. Since smaller diodes generate very little heat, it’s rarely a problem to have the LED touch a model’s interior surface. A large number of high-power LEDs in a confined space can be a problem, but much less of a problem than the blazing heat of incandescents!
LEDs are so long-lived that most people don’t have any qualms about gluing them down and sealing them up in enclosed models. An exception might be professional large installations where expected run times are in years or decades. In such cases some form of easy access - openable panels, running the LEDs and their wires through drinking straws, etc - is a good idea. And, as noted, high power LEDs for car headlights or spotlights or room illumination or whatever (many COB based LEDs) will get very hot and can’t be used this way.
It’s also best to test your whole lighting rig, fully powered up, before making the final commitment and gluing everything shut. Just because it’s so easy to make a mistake while wiring!
And remember that any batteries must be accessible. Alkaline cells can leak corrosive liquid once they lose power, and rechargeable lithium batteries have a chronological lifespan of only a few years regardless of use, and will need to be replaced.
Fibre optics
Fibre optics are extremely thin cylindrical strands of transparent plastic. They guide light from one end to the other, with very little light escaping out the sides. The idea is to put a light at one end, and have most of it shine out the other. (an "end glow" fibre) There are a few points to keep in mind.
I'm just talking about thin plastic fibres, not the hairlike glass fibres used in high speed data networks. Plastic fibre is thicker and more forgiving than data fibre, which isn't suitable for model making.
Plastic fibre is available in many diameters starting at 0.25mm, and increasing in 0.25 to 0.5mm increments. These smaller sizes are perfect for tiny models, but remember that the really fine fibres (0.25mm, 0.5mm) don't let much light through compared to the larger diameter ones. Test first if you need a bunch of lights of different sizes to have similar perceived brightnesses!
The fibres are fairly flexible. You can bend them into smooth arcs to install them. However if you make too tight of an arc the plastic will collapse, bend sharply, and no longer transmit much light at the bend point. The thicker the fibre the more resistant to bending. Note also that you won’t want to put the fibres in a location where they’re bent back and forth continuously, like a hinge. They probably won’t hold up to repeated bendings too well.
Light from a fibre is highly directional and not useful as a diffused light source. But it’s perfect for other tasks, such as making tiny headlights for automobiles, for traffic lights or rail signals, or countless other model railway applications. They’re also perfect for creating intense spots of light on a model spacecraft or building. Many movie models, such as the Star Destroyers in the Empire Strikes Back, used thousands of fibres to give the impression of a vast city-sized spacecraft with tiny little windows. Control panels and dashboards on cars or aircraft can be lit with fibre.
That brings us to another major benefit of fibre. Since the fibres can be really tiny in cross section you can use them to illuminate extremely small models with the actual lamp positioned elsewhere. In the age of large incandescent hot lamps, this was really important. Now with small cool LEDs it’s less critical but still a factor.
Finally because a while bundle of fibres can be lit by a single LED or light bulb it’s a great way of making complex-looking lighting, with a minimum of electrical wiring. The drawback here, of course, is that big fat bundles of fibres are kind of a hassle to route and install.
Fibre colour
You sometimes see multicolour fibre optics for sale. This stuff is pretty pointless because it usually doesn’t have a solid core of coloured plastic. It’s usually just ordinary untinted fibre that someone has dunked in coloured transparent paint.
So when you trim your fibres to fit, you cut off one of the painted ends. Now you’ve lost half whatever colour you had, since paint running along the sides is useless and doesn’t affect the output colour one bit. If you then trim the other end you get no colour at all!
You’re better off buying normal fibre, and a bottle or two of clear acrylic paint, such as the stuff that Tamiya makes. That way you can tint the ends of your fibres any colour you want. You can mix colours to provide subtle variations in tint. You may also just want to use a coloured light source with normal fibre.
Side light fibre
Most fibre is designed to carry light down the axis of the fibre. However some fibres are billed as side lit. These are slightly rubbery and less brittle fibres generally, and they emit some light out the sides.
The ones I’ve tried have been fairly useless unfortunately. They emit very little side light, and that only patchily. Maybe you’ll have better luck with something else.
Drilling holes for fibres
Installing fibre optics isn’t particularly difficult - you just drill a hole and stick the fibre in. However, there are probably a few points worth mentioning.
Since you’re probably going to be installing very thin fibres - maybe 0.25mm, 0.5mm, or 1mm in diameter - the holes are also going to have to be really tiny. This is really fiddly and time consuming to do. So:
You need drill bits that are just slightly larger than the fibre you want to fit, to allow a little room to manoeuvre.
You’ll want to buy a whole pile of bits, since you’re inevitably going to break tons of them. One excellent source of teeny tiny drill bits is people selling printed circuit board carbide bits on auction sites. These are used for automated hole drilling, and come in many sizes. They’re cheap and are often used. However, the fact that they’re no longer sharp enough to cut fibreglass circuit boards quickly is hardly a problem if you’re going to be drilling holes in models! They’re still plenty sharp enough for soft styrene or wood.
These carbide bits typically all have the same shaft diameter, decreasing to a very narrow cutting section.
If you’re just drilling a hole or two you could do it by hand. Hold the bit with your thumb and forefinger and rotate carefully. However it’s really easy to snap the bits this way. Lateral (sideways) pressure is what breaks the bits, not vertical pressure, so don’t tilt the bit off-axis.
You could also use a small twist drill. These "pin vice" drills either extend into a rotating disc that fits in your palm, or else have a spring loaded shaft that rotate as you press down. These take some experience and technique to use effectively without breaking bits.
If you’re drilling tons of holes an electric drill is always a good bet. However you need one with a chuck collet that can accommodate the tiny bit shaft - sometimes that requires adapting with a bit of brass tubing.
Tamiya make a low speed drill that works for this sort of thing. The advantage is that the lower rotational rate reduces the risk of the plastic melting. High speed tools, such as non-adjustable versions of Dremel tools, aren’t great for this.
If you’re drilling a row of holes to eg: simulate a bunch of windows it’s a good idea to scribe a guide line with a ruler. Just deep enough to keep the bit from wandering when you start to drill. A wonky line of lights always looks amateur and unconvincing, especially in a photo.
Similarly drill from the outside surface, going in. First, it’s easier to align your holes from the starting point as it were. And second, sometimes you get jagged edges on holes where the tip of the bit bursts through.
Paint before fibre trimming
The most common approach to installing fibre on something to be painted, such as a vehicle, is to drill the holes, fit the fibre, leave the ends protruding a little bit, paint the model, and then trim the ends flush with the painted surface.
This minimizes the amount of unlit area, lets you hold the fibres in with the paint, allows the paint to fill any tiny gaps between hole and fibre, and so on. Sprue cutting tools, which cut sideways to a flush finish, work well for this. Just be careful if you want to use solvent-based washes which may damage the plastic fibres - test the solvent with a scrap of fibre first!
SuperGlue eats fibres!
You may want to use glue of some type to hold your fibres in place. You have to be careful with this, since the fine plastic fibres are instantly destroyed by model kit cements, superglues, and other solvent-type substances. Superglue in particular is not an obvious threat, but actually causes the fibres to turn brittle and break.
Instead you’re best off using something like white glue/PVA. It will stick firmly enough to plastic surfaces to keep things from shifting, but can be easily pulled off if you need to move something later. Epoxy can usually be used if you want something that will never move. Some people also use thick opaque paint, such as glossy t-shirt paint, as both an internal light blocker and a medium for keeping fibres in place.
Lighting the fibres
Feeding light to a fibre isn’t hard - you just shine some light into the non viewing end of the fibre. However for maximum light efficiency you need to ensure that the light from your LED (or whatever source) is perfectly parallel to the fibre itself. The easiest way to do this is to take a brass or plastic tube just big enough for the LED to fit into. Cut the tube to a good length for you to stuff all the fibres in at the other end.
You can then use tape or glue to keep everything from shifting around - just be sure to use a fibre-compatible glue and don’t get any opaque glue onto the LED lens or the fibre ends! Tape isn’t always a good bet as many forms of tape dry out and flake off over the years.
If you’re installing tons of fibres in a model you have to do a little planning in advance. It’s worth working out how many fibres you need for a given area, then determining how many LEDs you’ll need on a per-bunch basis.
This also lets you design groups of fibres which flash - you just feed the fibres to their respective LEDs. Or have a single fibre in each bunch which leads to a flashing LED to avoid the problem of too many light points blinking together in an unconvincing fashion.
For example if you’re lighting a distant city model or the windows of a mighty starship you could put a handful of lights on a 30 second or 1 minute cycle, to simulate occasional lights going on and off. You just won’t want to group the lights going on and off too closely together, as it doesn’t look convincing when a whole batch of lights go off simultaneously.
Lensing the fibres
One popular way to finish a fibre end is to hold it briefly next to a flame - a candle or cigarette lighter. This causes the tip of the fibre to heat up and melt. If done right you’ll end up with a perfect dome-shaped lens at the end of the fibre.
This is called “lensing” or “mushrooming” the fibre. It gives a clean uniform finish, directs the light a bit, makes the fibre look a bit like a car headlight, and widens the end so the fibre can’t fall out. Just don’t hold the plastic close enough or long enough near the flame to burn it! It can also take a bit of practice to get identically sized lenses.
Computer panels and the curse of excessive blinkage
There are three common approaches people take to lighting cockpits or SF computer panels: static lights, Christmas on speed, and blinded by the light.
Static lights.
Steadily glowing lights are actually just fine for most models, such as those of real-life military vehicles or civilian aircraft. That’s what real life panels generally look like, after all. I see nothing wrong with this approach, which is far classier than the next option.
Christmas on speed.
The opposite extreme. Tons of lights flashing simultaneously! Big groups of lights, alternating back and forth. And flashing reallyreallyfast! Crazy colours like lime green and radioactive purple! Woooo!
What the hell? There's nothing remotely convincing about lighting like this unless you're building an alien disco. Alternating banks of light look particularly toylike and phony. Why do people do it?
Blinded by the light.
Then there's the stupidly bright cockpit idea. As if your crew are going to have to don sunglasses or welding goggles while they fly. Model lighting should be to scale and should look halfway real. A bazillion watts of light do not look real. Just like paint colours, lights should be scaled to the model.
Making it look blinking realistic
The key to believable instrument lighting is to make the blinky lights look like they must be going on and off for a reason. Take a look at cars and appliances and stuff in real life. The only lights that flash are trying to communicate something. And they only flash rapidly if they need to warn you of something major.
However movie sets, particularly those from the 60s and 70s, don't follow his rule. To keep the viewer engaged, set designers can’t help but stick blinky lights into a SF set, just to inject life and pizzazz. The thing is, banks of gratuitous blinking lights always look totally fake. Of course, if you're making a model of the Adam West Batcomputer then this may be fully accurate to prototype!
Or take the first Alien film. Its corridors and bridge had pretty convincing lights. But its computer room, with white padded walls, was covered by blinking lights that just looked like strings of Christmas lights had been slapped up.
There's actually quite a difference between Star Wars and the Empire Strikes Back in this regard. Empire's lights look far more convincing and sophisticated. The sets feature lots of steady lights with occasional solitary blinkers. Star Wars, however, often has entire rows of lights blinking away together in a way which looks really fake. Compare the hold's nav computer console aboard the Millennium Falcon, in Star Wars versus Empire.
So. The key points are:
Keep blink speeds low. Rapid flashing looks toylike.
Look at the thing you’re trying to model and, if it has animated or flashing lights, try to replicate its patterns and speed.
Obvious patterns over the course of a second or three, unless they have a specific contextual meaning like a chase light pattern, tend to look fake.
When possible, program in complex blinking patterns, or else flash many lights totally at random.
Big groups of blinking lights are obviously a giveaway. Especially when they're all in a row or alternating back and forth.
Don't blink everything. Most lights should glow steadily, with just a handful of blinkers to spice things up.
Maybe not everyone is going to sit and stare at your model, watching the lights blink. But it's good to keep it looking realistic for a casual viewing.
Subtle LED issue #1: colour quality of single-colour LEDs
One subtle difference between a colour-tinted light bulb and a single-colour LED involves the specific frequencies emitted and how the eye sees them.
Light bulbs produce white light, which is light covering all visible frequencies. To change the light’s colour you have to apply tinted transparent paint or install a colour filter. This filtration blocks some of the light from going out. The frequencies of light that actually do pass through correspond to the perceived colour.
Non-white LEDs are different. Their chips are designed to produce basically a single frequency of light, and only that frequency. (more or less anyway - they’re not as precise as lasers) You’re not producing all visible frequencies and then throwing most of them away by filtering them out. And that means that single colour LEDs look subtly different from filtered white light, even though both may be red, say, or yellow.
This difference is noticeable to the eye if you’ve spent time working with different types of lighting. But it’s really noticeable when it comes to model photography.
Non-white LEDs, especially blues and reds, produce light that seems to overwhelm the digital sensors used in cameras. You’ve probably seen this if you’ve ever taken a photo of an LED-lit model with your phone. Areas with direct LED light, or mostly lit by that light, will look blown out and blocky.
It’s not just model photography that’s affected. Concert photography has this problem, since a lot of stage lighting uses LEDs these days. Even big budget movies shot digitally can show this effect. Interestingly, chemical based film seems a bit less affected as it’s less likely to blow out in highlight areas.
Most people aren’t going to notice or care about this. But if the LED look bothers you, you could always experiment. Use white LEDs and then use the old-skool method of applying transparent acrylic coloured paint. Felt-tip marker pens don’t work very well: the dye isn’t concentrated enough to tint the light as effectively as transparent paint.
Using filtered white light sources is obviously less energy efficient, but it also means your colours will cover a slightly wider spectrum of wavelengths. You can also mix your transparent paints in different ratios for a range of slightly different colours. These techniques don’t eliminate the problem - you’ll still see blocks of colours in areas photographed digitally - but should reduce it.
Subtle LED issue #2: LED illumination speed
One subtle difference between incandescent light bulbs and LEDs is the speed at which they light up. Incandescent bulbs take a split second to heat up and produce light when current is applied, whereas LEDs generate light essentially instantly.
So for an added touch of realism you could program a microcontroller (chapter IV) to ramp up the brightness of your LED over a fraction of a second, and gradually decrease it when you power it off. If the software you’re using supports function calls you could write your own function to do this easily.
This affects the appearance of flashing lights on vehicles, for example. (Think of the way modern police car lights strobe so rapidly and violently) Or the way headlights on older cars illuminate and extinguish more slowly. Have a look at the beginning of the space slug scene in the Empire Strikes Back, for example - the Millennium Falcon’s headlights don’t snap on instantly.
Incidentally, have a look at the turn lights on cars. Some newer cars use LED turn lights, and they snap on and off instantly. Older cars use incandescent lights, and their turn lights ramp up to full brightness over a very subtle and brief, but still noticeable, fraction of a second.
Making LEDs look less like LEDs
One criticism of LEDs is that they can lend a toylike look to a model. As time passes and LED lighting becomes more ubiquitous in everyday life this may become less of an issue, but it’s still a point to consider.
Many of the ideas in this list are things that most people won’t consciously notice. But collectively they help provide a subliminal sense of realism that’ll help sell your model to the viewer.
Cool and warm white.
As discussed earlier, generally speaking you want warm white LEDs. They look more like lighting in real life. There are some instances where you might want cool blue - let’s say you’re making a model of a laundromat/launderette for your model railway, and want harsh cold fluorescent-style lighting. Or you've got a model of a car with xenon HID headlights. But on the whole it looks better to have warmer versions of white.
Avoid tricolour LEDs for white.
LEDs which produce white by emitting red, green, and blue light normally emit a less convincing white than phosphorescent white diodes. RGBW devices are thus much better at making white light than RGB devices, since they have a dedicated white diode.
Eschew the blue.
Blue LEDs have a strong intensity to them that looks like nothing else. The colour just screams, “LED!” They also photograph badly – blue LED light in particular seems to swamp digital sensors. So unless you’re making a police car model or something I’d avoid the telltale blueness of blue LEDs.
This ain't no disco.
As above, avoid those tricolour LEDs that change colours rapidly. Awful crap that doesn't look like anything in real life.
Flashing lights.
As noted above, control panels for planes or spaceships covered with a dizzying array of fast blinkies are a surefire recipe for a toylike appearance.
High refresh rates.
If you’ve got a dimmed LED with a low refresh rate you’ll get bad flickering. This can particularly be an issue with Neopixels (see section IV) and other such devices. There are different iterations of Neopixel-type LEDs with varying levels of flicker and pulse, and it makes a difference to get the ones with a rapid refresh rate.
Low refresh rate LEDs can leave dash and dot trails to the eye when you move a model, and can flicker horribly when recorded with a video camera.
Keep your colour selection subtle.
Sometimes you see a model that’s incorporated every possible single-colour LED on the market. Blue. Orange. Red. Green. Violet. But that sort of colour palette doesn’t match what you see in the real world, unless you're visiting a night market or something.
So keep your colour choices in a subtle range for increased believability. You could, for example, apply thin layers of yellow or blue transparent paint to white LEDs to get a very slight colour variation in output.
Make sure the LED isn’t visible.
This is kind of obvious, but make sure that the plastic LED isn’t actually visible, especially when it’s off. That immediately takes the viewer out of seeing the model as something else. The lemon yellow bit of a white LED looks particularly wrong for things like car headlamps or dollhouse ceiling lights. So hide the LED behind diffuser panels or fibre optics or anything, really.
Single-colour LEDs – colour quality.
See issue #1 above.
Brightness ramping and illumination speeds.
See issue #2 above.
LEDs versus tungsten
So here's a real-world (kind of) example. LEDs are often used on control panels and the like. But back when, up until the 1970s or so, small tungsten light bulbs were used for this purpose. To the casual observer they aren't going to look that different, but there are subtle and noticeable differences in the way LEDs will appear compared to small bulbs - issues 1 and 2 above.
One way around this issue, if you're going for an ultra-realistic simulation of an old-style control panel, is to use an LED device capable of changing colour and brightness. It is, for instance, possible to program a computer controller to get a Neopixel device to simulate a tungsten bulb accurately. It's a lot of work for something that most people won't notice, but it is pretty cool nonetheless! Here's an example of such a project.
The previous section
III: Powering LEDs.