With constantly improving lumen output capabilities, the little lights show big potential for neon lighting applications
Having already established a strong presence in exit sign and traffic signal applications, light emitting diodes (LEDs) are starting to enter illumination markets once considered out of reach for such a physically small technology. And now that they're making their way into cove lighting, wall washing, architectural/landscape illumination, and even entertainment lighting, it could be just a matter of time before LEDs begin to offer lighting designers a viable alternative in most neon lighting applications. Although these little lights that were once useless for anything other than indicator applications still lack the power necessary for full sign illumination, lighting designers may discover they're becoming more versatile all the time. Of course, the success of such a transition will depend on how well LEDs can mimic neon's shape-shifting and lumen output capabilities for signage applications, which will in turn depend on the similarities between the two technologies' physical properties. So just how alike are the two technologies?
In scientific terms, neon is a gas. But in the sign/lighting industry, it usually refers to a custom-made tube that produces colored — and sometimes white — light in a variety of shapes and lengths. The method by which a neon tube actually produces light can best be described by discussing its close relative: the cold cathode lamp.
Like neon lights, cold cathode light sources consist of a long formable glass tube that's coated on the inside with phosphors and sealed at both ends with an electrode, or filament. The tube is filled with a gas mixture of mercury and small amounts of argon and neon that produces ultraviolet energy when ionized by a high voltage applied across the electrodes. This ultraviolet energy, in turn, activates the phosphor coating on the inside surface of the glass tube to produce visible light.
Cold cathode lighting is made in 40 different shades of white and the three primary colors of red, blue, and green. Cold cathode tubes have a life expectancy of about 15 years — slightly longer than their accompanying transformers. Certain systems can achieve light output of 800 lumens per foot. The technology is typically used in back-lit displays.
On the other hand, neon lighting can produce as many as 110 colors — including white — to blend or complement any color scheme. The life expectancies of neon tubes and their accompanying transformers are similar to those of cold cathode lighting systems (Fig. 1 at right). However, electronic transformers, which offer 50% energy savings and improved performance, are available as an alternative to standard coil-and-core magnetic transformer models. Though not as strong as cold cathode lamps, some neon lighting systems are capable of producing light output of 600 lumens per foot.
Neon lamps don't typically require maintenance during their lifetime. However, as with every electrical sign, in addition to periodic cleaning, the electrical parts and connections should be inspected at least annually by an electrician experienced in servicing neon signs.
From an appearance standpoint, LEDs have little in common with neon lights. In fact, the typical LED looks much more like a microchip. In most configurations, a square diode chip the size of a grain of sand is encased in a plastic, epoxy, resin, or ceramic housing. Within this covering, the chip is attached by wires to an electric power source. When current flows across the junction of two different materials, the chip produces light in one or more wavelengths (color). The composition of the materials determines the wavelength(s).
Although many LED manufacturers predict their products can last as many as 100,000 hr, that number is dependent upon several of operating factors. LED lumen depreciation is affected by a variety of environmental conditions, such as ambient temperature, humidity, and ventilation. Control methods, thermal management, and current levels can also shorten life.
Aside from those considerations, though, LED technology boasts a relatively high efficacy, small size, fast strike/restrike time, ease of dimming and control, and safe handling, thanks to 12V and 24V power supplies. LED units can also use an electronic control system to provide dimming and color change operations (Sidebar below).
The luminous efficacy of a typical high-brightness LED is presently about 25 lumens per Watt (lpW), and that figure should rise to 75 lpW by 2007. But these numbers only tell part of the story. Because LEDs are completely different from incandescent and fluorescent sources, they can't be viewed simply on a lamp vs. lamp basis. And besides reduction in power use and lamp life extension, other “cost-of-use” factors should be considered, including color rendering. Since the composition of the materials determines the color of light produced by the LED, this solid-state source is energy-efficient wherever colored light is required. In the past, red light was produced by placing a color filter in front of an incandescent or fluorescent white light source, thus wasting a large part of the spectral energy radiated by the light source.
This makes LEDs attractive for all types of display applications where color and other attention-getting features, such as rapid on-off flashing, is important — applications that used to be the exclusive domain of neon. Despite these color rendering and restrike capabilities, though, it remains to be seen whether LED technology can completely replace neon.
The main event. LED devices can't compete with neon in the general sign market, in terms of lumen output per linear foot for direct light applications. But they can be competitive in certain types of signs and displays like channel lettering (Fig. 2 at right). Border tube systems, in which linear runs of thin neon lighting that are installed as feature strips on canopies and buildings, are also an option.
Currently available in red, red-orange, amber, blue, cyan, and green, LED channel lighting systems can be used in retrofit or new construction projects. One manufacturer ships its channel lighting products in reels, allowing the strips to be cut to size on location. LED strips, or modules, can be used in a wide variety of sign script fonts. In addition to allowing a faster, more efficient installation process, the LED modules essentially eliminate the possibility of breakage during shipping and installation, a problem that has plagued neon lighting equipment. Manufacturers provide detailed technical data and product information that specifically recommends equivalency guidelines equating the LED source to a neon source — for example, two modules for every foot of neon. The channel-letter “cans” that house the lights typically have an acrylic translucent sheet that cover the face of the letter and mask the LEDs.
A border tube system achieves the appearance of neon while offering lower installation and maintenance costs. It can also provide as much as 70% savings in power usage, and it's UL Listed as a Class II system. Generally, a border tube system includes pre-manufactured corners that make field installation possible, and cut pieces can be used, avoiding waste. One outdoor-rated power supply can typically supply 64 linear ft of tubing.
Impressive though these new capabilities and applications may be, it could still be several years before LEDs even threaten to replace neon lighting. The fact remains, though, that the technology continues to evolve at a pace that could soon make it far more than just a fringe lighting option.
Consider a cluster of individual LEDs arranged into channels on a panel to provide separate control of each channel. The first channel is red, the second is green, and the third is blue, and these three separate rows are repeated along the length of the panel. By switching one or more of the channels of LEDs on and off thousands of times per second, the apparent intensity of light is varied, but the human eye sees the light output as steady and smooth.
Altering the output of each channel over a wide range, through a control system, creates a wide variety of light intensities and color hues. Thus the three primary colors, or channels, of red, green, and blue can produce millions of different colors.
Consider also that a single fixture can be assigned a unique network address. A number of these fixtures can be incorporated into a total networked lighting system, which consists of the fixture, the controller, and the power supply.