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Bendy Beams

Fibre optics is the most flexible(!) form of in-car illumination - and now you can DIY!

Words by Michael Knowling, Pix by Michael Knowling and Julian Edgar

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This article was first published in 2002.
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If there's something inside your car that needs a touch of night time illumination, nothing comes close to the flexibility and performance of fibre optics. Forget messing around with ugly bulbs (and their clumsy mounts) - if space is tight, fibre optics are 'it'.

What are fibre optics?

Fibre optics refers to the technology that uses fine polymer threads to 'pipe' light. When light enters one end of the cable, it bounces through the inside of the cable filament to eventually shine out the other end. This particular type of fibre optic is commonly known as 'end glow'. End glow fibre optic cable can be bought in various diameters, typically from 0.25 to 2 millimetres, and is able to be bent through quite sharp angles. The colour of the light emitted is derived from the light source. In other words, shine a coloured light in, you get a coloured light out.

Installing Fibre Optics in a Car

The Necessary Hardware

Installing fibre optic illumination requires only a handful of components.

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The starting point is the fibre optic itself - we bought our supplies from www.thefiberopticstore.com and found their service fast and effective. Multiple cables can be used in parallel - simply tape one end of the cables into a tight bundle before connecting them to the light source.

Next, you'll need to come up with a light source; we started off with a cheapie 5mm green high intensity LED that we had lying around. High intensity LEDs are available in red, yellow, green, white and blue illumination - perfect to suit the vast majority of dashboards.

Note that the output of the LED is largely responsible for the amount of light that gets shone from the fibre end. High intensity 5mm LEDs start off at less than $1 for one that puts out 80 mcd, but you can spend up to around $8 for one that spits out a massive 6000 mcd.

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To control the amount of current passing through the LED - and, therefore, prevent it blowing - you'll need a resistor of around 670 ohms. This is soldered onto the positive side of the LED (which is the one with longer prong).

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To channel the light from the tip of the LED through the length of the fibre optics we used a short length of silicone rubber hose. Any type of hose will do, so long as it's a snug fit over the LED and the base of the fibre optics.

Installation

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To show how effective fibre optics can be in an automotive application, we decided to illuminate the power window switches on the door of a '92 Honda Accord. In standard form, there's no lighting for these switches, which makes them a bugger to find at night.

The first step of the installation process is to decide on a location for the fibre optic - in this case, we decided to locate the fibre optic immediately below the interior door handle trim to shine light down to the switch panel. There's a substantial 15-odd centimetres between the handle and the power window switches, which meant we were likely to need a high-power LED capable of shining 'long range'.

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As we expected, the low-power LED we hoped to use was not powerful enough to shine the distance required - it barely lit the outline of the switchgear. The answer was to move up to a more powerful 6000 mcd green LED - this was purchased from Jaycar Electronics for AUD$7.80 (part number ZD-1779). Once fitted, the new LED put out significantly more light - just right to provide 'soft lighting' for the switches.

We tested two different fibre optic combinations on the Honda - twinned 2mm cables and a bunch of four 1mm cables. As you'd expect, given the similar total cross sectional area of each combination, there wasn't much difference in terms of light output. The decision whether to use the twin 2mm cables or bunch of four 1mm cables therefore came down to the available space - we opted for the 1mm stuff because it was easier to squeeze out from behind the door handle trim.

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One of the great attractions of fibre optic is its ability to be flexed into the desired shape. The finest cable available (0.25mm diameter) requires a minimum bending radius of 9mm, while the thicker 2mm cable needs a 20mm radius. In practice, however, even the 2mm cable is amply flexible for use in a car.

And what happens if you bend it too tightly? It snaps!

In the Honda, we connected the LED into the dashboard lighting circuit so that the switches were illuminated whenever it got dark enough to call for the headlights. We ran hook-up wire along the bottom of the dash, through the factory sleeve that leads into the front of the door and then routed it up toward the door handle (ensuring that the power window, locking and door opening mechanisms weren't fouled). A small diameter hole was drilled through the door trim immediately behind the plastic recess for access to the interior door handle. Finally, the fibre optic ends were passed through and bent downward to point at the switchgear - easy.

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Fibre optic cable can easily be cut with a pair of scissors, but it's a good idea to afterward tidy the end with wet and dry paper. This ensures maximum lighting performance.

Oh, and - depending how you want to use it - you may need to shield the end of the cable from direct line of sight. The cable tip is very bright when viewed from either side or frontal angles, so - in the case of the Honda - we poked the fibres back behind the door handle trim slightly. This keeps the tip j-u-s-t concealed.

The Result

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Fibre optics is ideal for unobtrusive in-car lighting. It's cheap, easy to work with and - of course - really flexible. The number of applications is limited only by your imagination.

Here's the end result we achieved on the Honda's power window switches - they're illuminated just enough to be identifiable without causing a distraction for nighttime driving. As mentioned, the tips of the cables are also fully concealed - a perfectly stealth installation.

Contacts:

The Fibre Optic Store
http://www.TheFiberOpticStore.com

Jaycar Electronics (Australia wide)
www.jaycar.com.au

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