Lighting The Millennium with New Technologies
Apr 1, 1999 12:00 PM, By Joseph R. Knisley, Senior Editorial Consultant
Remote source lighting and electrodeless lamps are just a few of the new technologies making their appearance as viable and practical product offerings.
With new light sources and lighting systems emerging, the future looks promising and exciting. Today, there's a newer and greater understanding about the quality of light.
Joseph Good, III, President of the Illuminating Engineering Society of North America (IESNA), gives us a perfect example. In his editorial (March 1999 LD+A), he reflects on a Department of Energy meeting he attended entitled "The Lighting Technology Roadman Workshop." A cross section of the lighting industry, including consumers, manufacturers, designers, engineers, architects, developers, owners, and educators attended the meeting.
Here's the group's "lighting vision." For the year 2020, lighting systems in buildings and other applications will:
- Enhance the performance and well being of people.
- Adapt easily to the changing needs of the user.
- Use all sources of light efficiently and effectively.
- Function as a fully integrated system rather than a collection of independent components.
Create minimal impact on the environment during manufacturing, installation, maintenance, operation, and disposal.
As a result, people will understand, value, and use the tangible benefits provided by these lighting systems. We've already begun this process with the development of some new and exciting technologies. Let's look at a few.
Remote source lighting (RSL). Although relatively new, the use of RSL is steadily growing. Offering a number of advantages in both indoor and outdoor applications, RSL is a technique in which light travels from its source through a medium to one or more remote points.
There are four types of material used in an RSL system:
- Glass fiber: a circular light guide made of glass with a diameter between 0.002 in. and 0.006 in. (about hair thickness);
- Small plastic fiber: a circular light guide with a diameter typically between 0.005 in. and 0.08 in.;
- Large plastic fiber: a circular light guide with a diameter typically between 0.08 in. to 0.47 in.; and
- Prism light guide: a hollow structure (square or tubular in cross section) with the walls made of a transparent prismatic material.
Both a fiber-optic (FO) bundle and prism light guide system make use of total internal reflection.
Here's how this works. Because the wall of a light-carrying medium acts somewhat like a mirror, light entering the guide traps inside and continually reflects as it moves down the path (until it comes out the other end or diverts).
The two RSL methods (FO and prism) don't really compete for the same applications, although there is some overlap in architectural highlighting. Most lighting professionals use FO systems primarily in small-scale projects, which require limited light output (such as decorative applications) and where the relative high cost per lumen delivered is acceptable. On a large-scale project, where you need greater light output, lighting designers choose prism light guides, typically available in 6- to 20-ft-long segments.
How long do the various materials last? Glass fiber basically lasts forever, unless it breaks. Plastic fiber is less susceptible to breakage, but IR and UV energy from the light source can cause deterioration. (The fiber can turn yellow and brittle with age, and the light output can dim and change color.) A prism light guide has an unlimited life, providing you don't subject the materials to excessive temperature, UV, or highly concentrated solvents.
Let's look at both types of RSL systems in more detail.
FO lighting system. There are three elements in an FO lighting system: the illuminator, light guide, and fixture.
Illuminator. This device couples the light emitted by a lamp to the input end of an FO light guide. It contains a lamp, reflector, and perhaps an IR or UV filter. As an option, the illuminator accepts a dichromatic glass color filter wheel to provide a continuous or fixed change of color. A computerized programmable controller can provide special effects, such as timed light changes or strobe-like bursts of light.
You can synchronize multiple illuminators and integrate them with music on a sound system. You can also vary them by time of day. Most importantly, the light coupling efficiency of FO illuminators has improved almost fourfold in the past few years.
Light guide. The light actually passes through this medium. It usually consists of a bundle of plastic or glass fibers or a single plastic fiber. The plastic or glass core of each fiber is coated with a cladding (a very thin layer of plastic or glass) that prevents light from leaking out of the fiber. An opaque or transparent sheathing and a plastic, rubber, or metal tube (used to protect and support the fibers) cover the fiber or fiber bundle.
If you use the light guide to project light from the end, you call it an end-emitting fiber. If the guide has a special construction that delivers light along the entire length of the fiber, it's called a side-emitting fiber.
In use, the side-emitting fiber looks like neon tube lighting. As a replacement, it eliminates many of neon's headaches, such as reoccurring maintenance requirements, fragility, need for a transformer, and an electrical circuit operating at just under 1000V (in residences).
Fixture (or fitting). You can use various types of reflective or diffusing fittings at the end of the fiber. They can serve as recessed downlights, wall washers, or track lights and can create a variety of other visual effects.
Establishing FO system standards. Because of the nature of FO systems, standardization of photometrics is much more difficult than for traditional lamps and fixtures. Since the light doesn't come from a single lamp in a fixture, it's more difficult to express the photometric data. Additionally, long fiber runs, bends in the fibers, and other installation variants all affect final light output.
To deal with this, the National Electric Manufacturer's Association (NEMA) formed the Remote Illumination Systems Section, a committee to define standards and test methods for remote lighting systems (including fiber optics and tubular light pipes). The committee is now creating a standard glossary of terms and addressing safety issues. Several manufacturers now supply photometric data for FO systems.
Prism light guide system. There are four basic elements in a prism light guide:
- A light injector, which is equivalent to an illuminator. It contains a reflector, lamp, and glass or plastic window that can filter IR and UV or add color.
- A housing, which is a rigid cylinder or backing to support a transparent plastic film coating (called an optical lighting film, or OLF).
- A light guide, which is an OLF having a prismatic surface on one side and a smooth surface on the other. At each reflection, 2% of the light escapes.
- An extractor, which is a second film that diverts light from its path down the light guide so the light leaves the housing at specific locations along its length.
A prime application for prism light guides is tunnel lighting. For example, 11,880 ft of prism light guide replaces linear fluorescent luminaires in the Callahan Tunnel in Boston. The prism light guide delivers uniform, linear light along the length of the tunnel while reducing lighting maintenance costs.
Other new technologies. Utility deregulation and other factors are speeding the penetration of new lighting techniques and technologies, including unusual lamp designs and advanced optics. Let's look at some recent lighting innovations.
Electrodeless lamp. The technology behind an electrodeless discharge lamp, or simply an electrodeless lamp, is more than 100 years old. Nikola Tesla first demonstrated the concept in 1891. Because of advances in electronics and changes in electromagnetic interference (EMI) standards over the last 30 years, this lamp type is now commercially available.
Instead of using an electric current passing between electrodes to excite the gas fill (mercury and argon) in the bulb (as with a fluorescent lamp), this lamp uses high-frequency electromagnetic energy.
One type of electrodeless lamp is the induction lamp. It uses an induction coil inside the bulb to excite the gas fill. Here's the sequence of operation. First, a radio frequency (RF) power supply sends an electric current to the induction coil, which is a wire wrapped around a plastic or metal core. Then, current passing through the induction coil generates an electromagnetic field (EM) field. This field, in turn, excites the mercury in the gas fill to create ultraviolet (UV) energy. Finally, when struck by UV energy, the phosphors coating the inside of the glass bulb emit light.
The induction lamp in our example is essentially a fluorescent lamp, so the amount of light it emits is proportional to the phosphor-coated surface area of the bulb. If you increase the size of the system to gain more output, the light is harder to control physically and optically.
For purposes of circuit sizing, the manufacturer rates the lamp at 55% power factor and 130% total harmonic distortion. This lamp may cause interference with television and other electronic systems. It's also rated for reliable starting at temperatures down to 32 degrees F and will maintain about 98% of its light output at this temperature. This is a significant improvement for cold environments.
Another type of electrodeless lamp is the sulfur lamp. It operates on the microwave discharge principal. Here's how it works. First, the magnetron generates a microwave field. The energy from this field then travels through a waveguide into a cavity. In the cavity, a glass ball rotates at high speed to stabilize the fill in the ball (necessary for a uniform light distribution). Finally, the microwave excites the gas fill (in this case argon and sulfur), causing it to emit light.
The technology behind the sulfur lamp isn't entirely new. The manufacturer has a 20-yr history of making microwave discharge light sources used for ultraviolet (UV) curing in the semiconductor and printing industries.
The sulfur lamp's bulb can last indefinitely, since the sulfur and argon in its fill don't react with each other or with the glass. The longevity of the magnetron is the limiting factor in the sulfur lamp's life.
With a prism light guide, the sulfur lamp is the light source in a variety of demonstration projects at industrial plants, post offices, train stations, and similar facilities. When used without the guide, the system has the lamp enclosed in an industrial lighting fixture.
The lighting community remains hopeful about the future of electrodeless lamps, but its success depends on a number of economic factors.
LED lighting. At least two manufacturers are developing and marketing light emitting diodes (LEDs) for use as an economical alternative to compact fluorescent, halogen, and incandescent lighting. Industry sources foresee the inevitable evolutionary LED developments as having a tremendous potential forreplacing older, less efficient light sources.
John Bullough, a research associate at The Lighting Research Center, Troy, N.Y., believes the first applications for LEDs in the general lighting market will be for task and undercabinet lighting. He sees downlighting and display lighting as other potential applications. However, Bullough doesn't see anyone using LEDs for general lighting (like a 2- by 4-ft fluorescent fixture) for a number of years. The LED chip, immune to shock and vibration, is a relatively efficient converter of electrical energy directly to light. It can have a lifespan of up to 100,000 hr. Since an LED produces no UV emissions and very little heat, you can use an LED light source near clothing or sensitive artwork. You can also put it into waterproof fixtures for fountains, pools, and outdoor mounting.
For years, only the red LED was a practical light source. People primarily used it in exit signs, because it creates a very directional form of light. But since 1993, we've seen the development of bright blue and true green LEDs. The production of these efficient colored LEDs is important because red, blue, and green form the primary colors in full-color displays. In addition, combining red, blue, and green LEDs can produce white light for room illumination. Not only are LEDs much longer-lived than the 1000 hr of a standard incandescent bulb, but you can also adjust the three-color LED combination to give the best color balance to the generated light. Flat panels can provide bright light that is 100% dimmable, uses no mercury, and requires no ballast.
A two-year-old firm in Boston sells a three-color LED lighting system that provides attention-getting constant changes of color and light patterns without gels or patterns. One product is a track-mounted, MR16-looking fixture that receives both a power and data circuit. It can generate more than 16 million custom colors and lighting effects. It's retail price is about $1000.
Another manufacturer plans to bypass the need to use a trio of LEDs in achieving white light by applying the same luminescent conversion principle found in neon lamps. By combining blue emitting diodes and luminescent dyes, a single LED can produce bright light emissions at altered wavelengths. The resulting mixture of colors is visible to the human eye as white light.
Sidebar: Why Use Remote Source Lighting?
The separation of the source from the illuminated area and the ability to light multiple locations with one source leads to several benefits.
Removes infrared (IR) and ultraviolet (UV) energy. We often call the light emitted from an RSL system "cold" because it contains no IR (heat) energy. The system filters out most of the IR as well as UV energy produced by the source. You can safely light materials such as textiles, paintings, and food products, since most of the degrading IR and UV energy isn't present in the light beam.
Solves personnel and security concerns. Because there are no electrical parts in the light guides, you can safely use RSL systems in classified locations, such as areas with explosive gases or in wet locations, like pools and fountains. The light guides also carry light instead of electricity. Thus, there's no electrical power in the vicinity of the light-emitting parts (a safety consideration), so there are no electromagnetic fields present where the light emits. This means you can use RSL systems in areas with EMI sensitive electronic equipment, such as a magnetic resonance imaging room.
Putting the light source outside of a secured enclosure, such as a display case of costly objects, means you don't have to open the display area for servicing. This prevents theft or breakage and disruption of climate control. Additionally, hiding the light source keeps it away from vandals.
Simplifies maintenance. Replacing a system using multiple lamps with one using only one lamp means you have to replace just a single lamp. You can put the light source in a convenient, safe, accessible place. This greatly simplifies maintenance. Consider a high-ceiling application, such as downlighting for an atrium or over an escalator. With an RSL system, you don't need scaffolding or lifts to reach the lamp and associated equipment/electronics because they're located at an accessible place.
Reduces energy consumption. An RSL installation, with a single, high-efficacy light source (such as HID) is more efficient than an installation using many less efficacious lamps. As such, you'll use less energy for air conditioning because RSL systems emit less heat than conventional systems.
Increases design freedom. There are no creative restrictions regarding any light design with FO or light guide lighting. That's because you're able to install "light" at almost any location and combine different light intensities and effects. An FO lighting system is completely unobtrusive, since only the end housing hardware is visible. Additionally, you can retrofit thin optical fiber cabling into the ceiling or wall of an existing structure.
Most manufacturers provide detailed instructions on how to mate an optical fiber run to a fixture or end fitting. In all cases, however, you must make sure you keep both the fixture and optical surfaces of the fiber clean and dust-free throughout the connection process. Any debris will reduce the amount of light delivered through the fixture.
Sidebar: FO Installation Concerns
Most fiber bundles attach to the fixture with a ferrule. This a tight-fitting sleeve that attaches to the free fiber end and helps to efficiently couple light to the fixture. Generally, ferrules come factory-made for a particular fixture. Manufacturers generally sell fixtures as part of an entire FO system, but they are also available as individual units for field design and installation.
Sidebar: Other Light Sources for RSL Systems
You can use any light source for remote-source lighting, although the ideal source is one with a small area of light generation and high lumen output. The key is to combine a well-designed reflector with the source to direct light efficiently into the light guide. Here are some commonly used lamp/RSL systems packages:
- A 20W to 75W low-voltage MR16 lamp and an FO system in museums and display lighting.
- A 70W to 250W metal-halide lamp in an FO or prism-light guide system for architectural and outdoor lighting.
- Tubular and compact fluorescent lamps in prism light guide light boxes, where you need a larger, diffuse source.
You can even use the sun. For example, a daylight harvesting system of mirrors or lenses transmits sunlight to FO or prism-light guide systems.