4W monochromatic LED lamps used as wall-washer
Light sources in exhibition design | Part 3 – LED and electroluminescent lamps, fiber-optic systems
LED – Light-emitting diodes
LEDs are currently experiencing huge success in exhibition lighting.
They have a very high efficiency, typically between 30 and 100 lumens per Watt, their lifetime is proverbial and they can be placed very close to exhibited objects because of their low surface temperature.
Traditionally, light color has been a problem; because of their technology, LEDs naturally produce their light at a very precise frequency, so obtaining natural light could be a very demanding effort for producers and it is often very difficult to get a correct color accuracy. Nevertheless, while in the past white light by a LED lamp was produced by combining three red/blue/green LEDs, now is common to get it in a single diode by adding a phosphor, thus high-quality LED lamps have greatly improved their spectral performances and the light they produce is often almost indistinguishable from that of halogen lamps.
Comparison between an old 9W LED bulb (top) and a more recent 8,5W one (bottom), showing the more balanced spectral emission at all visible light wavelengths of the latter
LEDs, that once were mainly used as a replacement for fluorescent lights in the same application range, such as in light boxes or for objects and artworks when light color accuracy was not very important, are now becoming a reasonable alternative to halogen lamps even in demanding exhibition applications.
Another claimed advantage of LED lamps over halogen and metal-halide lamps is their low emission at Ultraviolet frequencies, which would help to preserve pigments and materials of fragile artworks. Nevertheless, there is still not enough experimental evidence on such matter, and the permanent use of LEDs for lighting, say, ancient paintings should be considered carefully, at least until enough data are available.
Fiber Optic lighting systems
Optical fibers are not actual lamps, they are a medium that transports light from a source to an emitter.
Nevertheless, I am covering them because, when coupled to a light source, usually called an illuminator, they contribute to very peculiar lighting systems, that can do things that no other systems can.
Optical fiber cables are usually made by a bundle of glass or plastic filaments, capable to transport light from one point to another with very low dispersion and absorption rates.
There are two types of FO used for exhibition lighting: side-emitting and end-emitting.
The first is mainly used for “eye-catching” effects similar to those obtained with linear fluorescent lamps and LED strips.
The seconds are used, like dichroic halogen lamps, for light-spotting small objects.
The light source of an Optical Fiber-based lighting system can be an illuminator provided with a Metal halide or a Halogen bulb, usually with an electric power ranging from 70 to 250 Watts.
A mix of side-emitting and end-emitting optical fibers used to achieve different lighting effects
An advantage of Fiber Optic systems is the good chromatic performances they provide, especially when coupled with a halogen illuminator, at the same time without overheating the illuminated object, which is often a requirement for very fragile artworks, artifacts, and specimens.
Another advantage, for example on dichroic halogen lamps, is that a single illuminator can “feed” several light emitters, to which various types of lenses can be attached so as to obtain wide or narrow light beams, and a precise lighting of small objects of very different size and shape, like coins, medals, stamps, cameos, jewels, gems, insects and so on.
The main drawbacks with FO are the high cost of the complete systems, the reduced luminous flux provided by each single emitter, and the need to place the illuminator rather close to the target (for plastic end-emitting FO it is usually recommended to do not exceed a distance of 7m from the illuminator to the fiber end) and in a secured and ventilated space.
For all these reasons, today LEDs are increasingly preferred to optical-fiber-based lighting, except for very specific applications where a dim light, but of the highest quality, is required, or when their peculiar expressiveness and appearance can make the difference.
Two monofilament optical fiber cables: a thin PVC-jacket cable and a thick unjacketed plastic fiber, photo Inexhibit
Electroluminescent / Light Emitting Capacitor
Light Emitting Capacitor (LEC) is a relatively new technology, it exploits the capability of certain chemical substances to emit light when excited by an electric current.
LEC lights usually come in thin flexible sheets emitting a very subtle, homogeneous light from one side of their entire surface. In exhibition design, they can be used to backlit graphic panels or to create large light-emitting surfaces, even with curved shapes.
The power consumption is usually very low and durability is acceptable, the appearance is often surprising and captivating because the light seems to “come from nowhere”, due to the thinness of the emitter. The light color is typically rather cold, the surface temperature never exceeds 40°. The typical spectrum of an electroluminescent light usually presents a narrow bell shape centered on a precise frequency, characteristic of the chemical substance adopted. A major problem with LECs is their low light flux combined with the complexity of the system, the lighting foil has to be connected to both a transformer and an inverter, making the whole pack heavy and expensive. Nevertheless, since this technology is suitable to produce very thin and lightweight screens for portable computers and mobile devices, we could expect further and promising development in the future.
A commercial electroluminescent sheet (inverter omitted) produced by the American manufacturer Ceelite, photo Inexhibit
LEC sheets are used in this exhibition to create thin backlit graphic panels, image courtesy Bianchini & Lusiardi Architects
Light sources for exhibition design part 1
Light sources for exhibition design part 2