Paul Ruffles, Principal, Lighting Design and Technology and Past-President, Society of Light and Lighting, asks a deliberately provocative question, after all he's a lighting designer who uses both fibre optics and LEDs, both for space lighting and for case lighting.
As with many technologies, it’s a case of horses for courses; in other words, some situations favour fibre-optics and other favour LEDs, says Paul Ruffles, Principal, Lighting Design and Technology and Past-President, Society of Light and Lighting.
This is a deliberately provocative title from a lighting designer who uses both fibre optics and LEDs, both for space lighting and for case lighting. As with many technologies, it’s a case of horses for courses; in other words, some situations favour fibre-optics and other favour LEDs.
Fibre optics
Fibre optics have been the workhorse for case lighting for many years. The optic lenses are small and can be neatly integrated into the tops or sides of cases to light across freestanding or shelf-mounted objects of all sorts and sizes. With fibre optics, the projector housing the lamp is kept outside the object compartment or even remote from the case itself. This not only avoids any heat from the lamp entering the object compartment but also allows easy access to the lamp for replacement without entering the secure object compartment.
The light is carried from the projector to the optics by thousands of fine glass or plastic fibres that are grouped together in various sized ‘tails’ that make up the ‘harness’ from a projector. The more fibres in a tail, the more light is transmitted by that tail. Generally, the tails are limited to ten metres or so in length to avoid light loss and a shift in colour of the light. The length and fineness of these tails from the projector to the case ensure that there is almost no heat or UV transmitted from the lamp to the object compartment.
The projectors can use tungsten-halogen or metal-halide lamps (and to confuse you a little, even LED lamps now). The tungsten-halogen projectors can be easily dimmable to adjust the lighting level in the case to the required conservation level as well as to allow the brightness of the case to be balanced against other lit graphics or objects near to the case. As the light is dimmed, the energy use also reduces and the lamp life increases. However if you go too far, the light shifts to a dingy orange, which is not a pleasing colour for your precious objects. Metal-halide projectors can also be dimmed with a rotary mechanical dimmer in the projector, but unfortunately it just blocks light as you dim so the lamp always runs at full power – no energy saving, but also no colour shift.
Disadvantages of LEDs
Of course LEDs can also provide small aimable points of light that can be ideal for emphasising objects in cases. In addition, the beam of light from a white LED has almost no heat (infrared light) or UV in it. However, there is an inherent problem – the LEDs themselves are hot. If you put 60 watts of LEDs in a case, then you are putting 60 watts of heat in the case (unless you have a way of conducting the heat from the back of the LEDs to the outside of the object compartment). So if you look at Figure 1, which shows one of a range of cases we designed with Casson Mann for the Manchester Art Gallery, you can see that the fibre optics were carried within a freestanding structural boom inside the glass box that made up the case. If these were now to be LEDs instead, you would need a system of heat piping to remove the heat from the backs of the LEDs (or accept that the case will heat up gently through the day and then cool down overnight, sucking in dust).
Looking now at room-sized applications there is more of a shift from fibre optics to LEDs. A recently completed project of mine was a room at the American Museum in Britain, where I replaced an aging fibre optic system with small recessed adjustable LEDs (see Figure 2).
Here, the output and distribution of the LEDs was an ideal match for the objects and displays in the room. The old projectors had been mounted on the roof of the room (a stage set within a larger space) and so had been awkward to access for relamping. It took just 18 one-watt LEDs to light the room.
In the photo of this room, you can see that the inclined display panels on the dividing barrier are well lit – it took just three of the LEDs with elongation lenses to light along the whole length of the panels.
Tailored solutions
But LEDs are not always the best answer for room-sized spaces. I have recently designed a fibre optic lighting system for the tomb in a new Egyptian gallery at Ipswich Museum. Here, three different sizes of ‘star’ optic have been used to create a pattern on the ceiling of the star formation Ursa Major and the surrounding star field. Fibre optics allowed me to use very small star optics and various-sized tails in the harness to get the different star brightness with just one light source. Another fibre optic system provides a separately dimmable set of wall wash optics to light down onto graphics on the wall. Wall-recessed and floor-recessed cases also use fibre optic projectors for the varied range of objects that will be exhibited in the cases. So to answer the question I posed at the beginning of the article: yes, we still do need fibre optics, but there is an increasing crossover in application between fibre optics and LEDs – one that will shrink as LEDs become more efficient and therefore cooler.
About the author
Paul Ruffles is the Principal of Lighting Design & Technology, a lighting design consultancy that specialises in museums, galleries and historic buildings. He lectures and writes extensively on museum-related lighting issues.
