lest we forget - fibre optics as a design tool

As the current trend is to promote the use of LEDs as a universal solution, it could be easy to forget that fibre optics can be used for many similar design applications as the LED. However, the use of fibre optics is often overlooked due to common misnomers, cost and the view that it is a specialist area of lighting.

I consider fibre optics a specialist area but have never let that scare me off specifying them. Over the years I have built good relationships with two fibre optic companies: Chris Burridge at Light Projects and Del Bennett at Group C Lighting. I rely on their expertise, detailed knowledge and above all their honesty. I have often involved them at early stages of design in order to achieve the effects that I have wanted and more importantly to tell me when what I want to do is impossible with this medium. Correctly using the tools in our lighting box is what our clients rely upon and the use of fibre is an area where we can often go wrong without this help.

The common misnomer about fibre is that it will not be bright enough to achieve the effects required at the distance needed. Careful consultation with a specialist resulting in a combination of fibre sizes and lengths means that the majority of light levels and effects can be met.

And whilst it is often a costlier solution, it should be remembered that your specification buys you a tailor made solution, designed specifically to suit your schemes' needs.

It is also possible to buy 'off the shelf' fibre optic kits that consist of a projector, a set length and thickness of fibre harness and various lens kits. Whilst these suit some standard applications (ie. lighting bottles in a back bar), anything sophisticated or more complicated requires fibres specified to suit. Specification is difficult without the help of a specialist as fibre lengths need to be measured accurately before production and there are many other companies apart from the two already mentioned waiting to help realise your design ideas: Universal Fibre Optics, Absolute Action and Crescent to name a few.

Although it is essential to respect the limitations of a fibre installation, the advantages and the flexibility afforded to the designer make it worth getting over your fears and including their use within a scheme. Most lighting consultants have a clear understanding of fibre systems and their applications but interior designers, engineers, architects and other fibre virgins are often unaware of the absolute basics. This means that fibre as a solution is often overlooked or its inclusion questioned.

The advantages of using fibre optics are based in the fact that the light source is separated from the light output. Thus the light does not radiate heat, has no current and the light source can be placed where is easily accessible for maintenance and the heat issue is no problem.

This means applications where UV or IR radiation is undesirable (i.e. in museums with fugitive objects), where there are safety issues (i.e. lighting to water features), for lighting within inaccessible areas where maintenance is difficult or expensive or for areas exposed to dangers of explosion are ideal.

Fibre optic lighting is also useful where fittings need to be very small and discrete or for decorative effects such a star ceilings. Sparkle or colour wheels can be used in conjunction with the fibre optic projector.

A fibre optic system consists of three main parts. First, the projector; this is a unit within which the light source is housed and concentrates the highest amount of light into the fibre harness. Tungsten Halogen and Metal Halide are the available light sources. There are a variety of wattages and projectors can be rated for indoor or outdoor use. Most projectors require cooling, and this is done by means of a built-in fan cooling the vital parts.

Second, is the fibre harness itself. This is the means by which the light is divided and travels (by total internal reflection) to its destination. The joint end of the fibres (known as the common end) is connected to the projector. Here the fibres are collected, smoothed and polished into a homogeneous surface that allows a maximum of light to pass through. Fibres can either be manufactured in plastic (PMMA) or glass.

The harness can contain fibres of varying or of uniform lengths and of varying or uniform thickness according to design requirements. Fibres can also be side emitting or end emitting.

Lastly, at the termination point of each fibre a fitting can be utilised. There is a huge variety of fittings available from decorative Swarovski crystal to precision optics. Fittings are used for aesthetics, for concentration of the light, to control the light, and to protect the fibre end, for instance against UV-radiation or water.

The following issues should also be considered; The colour temperature of the light changes according to the length of the fibre, and differs between PMMA and glass and also between Metal Halide and Tungsten Halogen. Glass fibre provide less light, but in a warmer colour temperature than PMMA.

Also in a fibre optic system there is a light loss between the light source and the common end, and a transmission loss inside the fibre itself. The longer the fibre, the bigger the loss. As the light from one source is divided and distributed to several or many light points, the intensity at each is smaller than the light source itself. However the flexibility afforded by numerous light points yields the lighting designer a high degree of freedom in their scheme.

It is also important to consider the installation process. Projectors require space and ventilation. Locating projectors nearer to the object or area to be lit shortens fibre lengths and saves costs. Fibre routes need to be thought through as minimum bending radii need to be taken into account.

So take the plunge, use the help available, forget your preconceptions, include fibre in your schemes and reap the benefits of this versatile and flexible lighting tool.

www.lightmatters.co.uk