No longer a novelty lighting scheme for pools and fountains, modern fiber-based can serve a variety of applications.

Once relegated to underwater environments, fiber optic (FO) lighting has made its way to dry land in recent years, becoming a viable alternative for specialized lighting applications. Conceived as a means for lighting pools and fountains, the technology has since been embraced by lighting architects for several indoor uses due to its low heat production.


In its simplest form, an FO system consists of the illuminator, or light source, and a number of fiber optic cables, or light guides, that carry the concentrated beam of light produced by the light source (Figure). In construction, an optical fiber cable is made up of a light-carrying core with a thin protective coating, or covering, called the cladding.

This fiber optic cable, or tube, employs a lighting characteristic called total internal reflection to carry the light throughout the length of the cable. The interface between the core and cladding of the tube wall acts like a mirror. The light entering the fiber optic tube is trapped within the core and is continually reflected as it moves down the path. Then it either comes out the other end or is diverted. The end-emitting fiber is usually covered with plastic, rubber, or metal sheathing tube for protection and support.

A less common type of fiber optic cable, called a side-emitting fiber, distributes the light from the illuminator along the entire length of the tubing like neon lighting.

The following fiber optic cabling types represent your most basic options:

  • Small-core plastic fiber is a solid polymer optical fiber typically 0.005 in. to 0.08 in. in diameter. It's clad with a thin material that exhibits a lower refractive index than the core, is available in any length, and can be field cut.

  • Large plastic fiber is a solid polymer optical fiber typically 0.08 in. to 0.47 in. in diameter. Large core fiber isn't as flexible as small plastic or glass fiber, and requires a fairly large bend radius. Connectors and cutters with Teflon-coated blades are sold separately for use with the large-core plastic material.

  • Glass fiber bundles (GFB) are made up of multiple cylindrical glass light guides with a diameter of 0.002 in. to 0.006 in., or about the thickness of a human hair. Unlike plastic fiber bundles, which can be field cut, glass fiber harnesses or tails are usually factory cut and assembled.

Care should be taken during installation so that the fiber tails aren't bent beyond the manufacturer's recommendations. In general, glass fibers can be bent up to 10 times the diameter of the light guide. If glass fibers are bent beyond 90°, some of the individual fibers might break, thus reducing light output.

Fixture characteristics.

Because FO products aren't standardized, components from one manufacturer can't be substituted for equipment from another. For example, a fixture will use a particular light source (and thus have a specific color temperature) and a specific type of optical fiber. In many cases, the light source's design and construction is unique to its manufacturer.

The size of the individual fibers and the required illumination level generally determine the necessary wattage and type of light source. The range of light sources extends from 20W to 75W MR16 lamps and 70W to 250W metal-halide lamps. Although low-voltage MR16 tungsten halogen lamps offer precise beam control from a tiny filament, several new compact metal-halide lamps offer similar optical performance. Consider also that the optical fiber is specified on the basis of the beam spread and focus of the lamp, the “angle of acceptance” of the fiber, the location of the fiber relative to the light source, and how the fiber is bundled.

An illuminator can be fitted with a dichroic glass color filter wheel to provide a continuous or fixed change of color before light enters the source end of the fiber. Additionally, the movement of a color wheel can be computerized to provide special effects, such as timed light changes or strobe-like bursts of light. In addition, two or more illuminators can be synchronized. Fiber optic lighting is ideal for these color change special effects. DMX 512, a common control protocol within the theatrical industry, provides computerized control.

Although several FO lighting manufacturers offer photometric data sheets, these aren't the same as the light distribution charts used for standard lighting fixtures. Within the National Electric Manufacturers Association (NEMA), the Remote Illumination Systems Section establishes some guidelines for fiber optic lighting.

Fiber optic lighting offers specific advantages for new and renovated spaces. For example, the light source can be put in any convenient, safe, and accessible location, thus simplifying maintenance. If the light source is located outside of a secured enclosure, such as a display case, the case doesn't have to be opened for lamp replacement or servicing.

The fiber bundles, or harnesses, and other equipment can be installed almost anywhere. For example, only the end housing hardware is visible in a down lighting system. Additionally, the ceiling or wall of an existing structure can be retrofitted with thin optical fiber cabling. Many objects, such as furniture, handrails, works of art, and a variety of other architectural and decorative elements can be lit with fiber optic end fittings.

The illuminator can use a filter to remove most of the lamp's infrared (IR) and ultraviolet (UV) energy, which can damage and fade the colors in textiles, paintings, and graphic art pieces. For that reason, this type of light fixture is ideal for displaying such materials, and can be used for museum lighting, which is a primary FO lighting market (Photo).

Since no electrical power is in the vicinity of the light-emitting parts, for safety reasons, fiber optic lighting doesn't create electromagnetic fields. Thus, you can use this lighting technology in areas with EMF-sensitive electronic equipment, such as a magnetic resonance imaging (MRI) room.

Because fiber optic lighting units are so versatile, you can select from several application-specific fixtures when designing a lighting scheme.

Down lighting type fixtures.

These hardware pieces are generally made of molded plastic or cast aluminum and come in a variety of designs and finishes. The housing usually contains a lens to provide some type of beam focusing. Their small size and flexibility allow for a variety of mounting positions. Decorative details can be achieved with some of the new models, including acrylic molds; high-quality crystals; and clear, frosted, or colored glass. Some downlight hardware pieces use a mounting sleeve, while others are secured with spring clips, screws, or some other method.

Wall washer and accent fixtures.

Often called eyeball units, these fixtures have adjustable sockets for ease of aiming. An adjustable lens is another component that allows the emitted light to be focused from a narrow to a wide beam. Units specifically designed for use in showcases or displays have a variety of beam shapes. Often fitted with numerous light outlets, these fixtures are positioned in mounting bars or rails.

Landscape and exterior fixtures.

These units, usually fitted with decorative elements, often illuminate a garden setting, sidewalk, or patio. Some outdoor fixtures have extremely flexible arms to allow you to aim them at specific areas. Other models can be buried in the ground or mounted in a concrete slab.

Underwater application fixtures.

The absence of electrical components makes fiber optics an ideal choice for swimming pools, whirlpools, fountains, and similar locations. Although many FO fixtures are waterproof, units designed specifically for submerged locations are available.

Specialty fixtures.

These hardware pieces provide tiny points of light and are usually made of clear, colored, or frosted glass.

Fiber optic lighting is no longer just appreciated for its novelty. Lighting designers are now becoming aware of its functionality and using this waterproof lighting technology for non-traditional illumination needs.




Sidebar: Terms to Know

Some useful terms used in fiber optic lighting include:

Acceptance angle

The maximum beam spread of light from the light source (measured from the fiber's axis) that will enter the end of the fiber.

Attenuation.

A measurement (in decibels/ft) of how much reduction in light is experienced per unit length of fiber.

Color rendering index.

Measures the degree of an object's color shift when illuminated by the light source, as compared with the color of the same object when illuminated by a reference light source of the same color temperature. The higher the number, the “truer” the object's color appears.

Connectors, couplers, and ferrules.

These hardware devices are used to join parts of a system physically and/or optically. A connector holds a fiber to a port or a fixture. A coupler aligns a fiber to the illuminator or two fibers to each other. A ferrule is a terminating device used to keep a fiber bundle properly positioned. Ferrules are usually factory-designed to work with particular fibers, so the installer simply inserts the ferrule into the fixture's connection sleeve.

Fiber optic port or master ferrule.

This metal or plastic connector is attached to one end of a fiber optic bundle, allowing it to be readily inserted into an illuminator for maximum light output. A manufacturer can assemble the bundle (called porting) before shipping, or porting can be done in the field to satisfy changing job conditions.

Fixture.

A hardware device placed at the termination of an end-emitting fiber distributes the light in a specific pattern. Fixtures are generally sold as part of an entire FO system, but they are also available separately. (Confusion is possible, since “fixture” is also the term used in the electrical industry for any type of housing distributing the output from a light source. A luminaire is another industry term for a housing containing a light source.)

Numerical aperture (NA).

The difference in the refractive indexes of the core and cladding determine the NA of the fiber. The NA is the acceptance angle for the fiber, above which light entering the core won't be guided by the cladding. In other words, it won't be internally reflected. A smaller NA doesn't necessarily mean better output. Other factors like angle modes have as much, or more, to do with output.