LEDs for Channel Letters and Beyond

Although neon will always have its place, light-emitting diode (LED) light sources are encroaching on its territory. Having conquered traffic signals, exit signs, outdoor video screens and scrolling-message displays, LED technology continues
to advance in quality, brightness, color and energy efficiency. Acrylic-faced channel letters and building accent strips are the logical next step.

No longer in its infancy, LED signage technology is entering that toddler stage. As new applications are proven, and high technology is priced to move, some overzealous mistakes may be made. But like a small child, LEDs won't be deterred. Pressure from property owners, utilities and government will push LEDs into the channel-letter and accent-strip markets…and beyond.

LEDs are solid-state devices that generate light without tungsten-coated cathodes or filaments. LED chips as small as a speck of pepper are produced as a wafer, like a computer's integrated circuits. The process of this first level of production is called epitaxy.

The chip is then mounted in a reflector cup (it acts like a tiny floodlight), wired and completely encased in epoxy, which protects the device and acts like a lens. This is what we think of as the typical, 5mm LED.

Different packages are available from various manufacturers, but there's a Catch-22. Manufacturers — Agilent/LumiLEDs, Nichia and AXT, among others — have found a market for certain package configurations, so they continue to produce more of the same. Buyers purchase those packages because they're available, not because the package is perfect for a particular lighting system. As the LED-illuminated signage industry matures, packaging will evolve when OEMs pressure manufacturers to improve quality.

Quality control in these delicate manufacturing processes is absolutely vital to an LED's longevity. And most definitely, you get what you pay for. An LED may appear flawless, but microscopic flaws, particularly in the epoxy resin, can lead to failure. Variations in quality can also occur in different areas of the same wafer, so LED chips are divided into bins at different price points.

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Quality packaging means positioning the chip within the reflector and attaching leads with excruciating exactitude. New technologies, using silicone instead of epoxy in packaging, may prove to offer better quality and, therefore, much longer life.

Viable lighting systems

OEMs turn packaged LEDs into viable lighting systems (Permlight is experimenting with proprietary packaging more suited to signage lighting). Many quality issues come into play at the systems stage, but the greatest are heat and moisture. Manufacturers can effectively guard against these issues, but not all do.

LED installation requires training and experience, although less than that with neon. Proper placement of LED modules and sealing of accent strips can keep out corroding moisture. The concerns are the same for most electric signs.

An LED chip prefers the cold but can operate efficiently at very high outdoor temperatures. This issue has been confused in the early adoption of LEDs in channel letters. The temperature at the light-emitting junction inside the LED is critical and must be kept below 212° F (100° C).

There are several ways to cool an LED installation. A large, permanent, outdoor, digital-video screen — like the NASDAQ sign in Time Square or Jumbotrons on the Las Vegas Strip — is packed tightly with LEDs. Usually, these signs will have a dedicated air-conditioning system; fans and convection-cooling designs can also be used.

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The hottest temperature the Weather Service ever recorded occurred in Death Valley in 1913, 134° F (56.7° C). Temperatures inside a channel letter, sitting in direct sunlight, can be outrageous, maybe even up to 176° or 194° F (80° or 90° C). But it's safe to say that the outside air temperature will always be cool enough for LED operation.

In channel letters, each chip can dissipate heat to the outside air — regardless of the ambient temperature inside the channel letter. This also allows retrofitting of existing neon-illuminated channel letters.

All light sources consume energy to create both heat and light. Today's LEDs create more light than heat per watt compared to incandescent bulbs, and they're rapidly approaching the efficacy (raw lumens of output per watt of electricity consumed) of fluorescent tubes.

However, it's the monochromatic nature of LEDs that enables the extraordinary energy savings of 80%-90%. Light comes in many different wavelengths (measured in nanometers) or colors.

Noonday sunlight has all the colors of the rainbow, as does a household incandescent light. But the incandescent lamp is much stronger in reds and yellows, the longer wavelengths (that's why it looks warm or yellowish). Put a conventional light source inside a red channel letter, and all the light energy in the red wavelengths will shine through, creating a fairly bright letter face.

But what happens to all the green and blue light energy that the incandescent lamp is emitting? The red filter won't transmit those wavelengths; instead, it absorbs the light energy and discards it. All the energy it took to create that light is wasted.

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However, let's try focusing energy into making only the light we need. The better solution, clear red neon (Ne), emits light strongly, but not solely, in the red wavelengths, which ideally suits red channel letters. But the best solution, red AlInGaP (pronounced Alan-gap, signifying aluminum indium gallium phosphide) LEDs, produce virtually all their light at a single wavelength (within a tiny range of approximately 50nm). We order red LEDs, not by name, but by wavelength — 630nm or maybe 615nm for red-orange.

LED channel-letter modules also have the edge because all lumens (the unit of luminous flux) emerge at the front. It can be directed to illuminate the face more efficiently. Neon radiates light 360° around the tube, but in channel letters and building accent strips, much significant light is lost into the back of the enclosure.

Efficiency attracts new markets

The success of LEDs in exit signs and traffic lights results directly from the color-efficiency issue. Back when LED efficacies (lumens per watt) were worse than those in incandescent lamps, red traffic signals and exit signs were still retrofitted with LEDs. They perform that particular job more efficiently because you only need red light.

According to Lighting Research Center data, typical wattage for a red, 12-in. incandescent signal is 135W, compared to 10W for today's LED model — that's 97% savings with equal brightness. Green LED technology (using InGaN [indium gallium nitride] chips) now offers nearly as much savings. When one incandescent lamp fails, that signal fails completely; but if one LED fails, it's barely noticeable.

Conventional signal lamps, which are built for durability, should be replaced annually; most LED signals are guaranteed for five years. Longevity alone saves municipalities hundreds of maintenance dollars a year per intersection.

LED traffic signals have been tested in field conditions for the past 20 years, while the most recent generation of technology has been tested perhaps only 10 years. Failures are rare and typically caused by manufacturer defect. In the interests of energy conservation, utilities and governments are providing "carrots," such as rebates and tax credits, to speed market penetration. I'll bet the streets in your town have LED traffic signals — or soon will.

The second tried-and-true LED application, exit signs, are universally replacing incandescent and compact fluorescent models. The Environmental Protection Agency's Energy Star program estimates that each LED exit sign saves its owner $15-$20 a year in energy costs, compared to older incandescent lighting, with less maintenance and better reliability.

Today's exit signs are guaranteed for five or 10 years, but LED retrofit kits carry 25-year, and even lifetime, guarantees. Some LED exit signs will outlast their buildings, while burning 24 hours.

Neon channel letters and building accent strips are the next major markets targeted for LEDs. Despite LEDs' higher initial cost (which will decrease over time), owners can save on energy costs, as well as maintenance. Existing applications have been in place for only the past few years. Where quality products were installed properly, failures are minimal. We expect 10 years' average life on these products.

These systems' energy efficiency depends on the transformers and number of resistors used in the LED circuit. Comparing equally luminous letter faces, depending on the color, savings estimates range from 75%-90%.

Independent testing is forthcoming. At presstime, public utilities in California are developing and instituting component rebates for LED retrofits: $2-$6 per foot of neon replaced, based on letter height and a standardized estimate of the length of neon contained therein. LED systems must demonstrate energy savings of 80% or better.

Since 1987, when President Reagan signed the National Appliance Energy Conservation Act, federal, energy-efficiency standards mandate that such products as refrigerators, electric motors and air conditioners meet minimum efficiency standards. Certain types of incandescent lamps and fluorescent ballasts are effectively "outlawed" for sale in the United States.

Efforts are underway to target exit signs and traffic signals, with environmental groups demanding maximum wattage standards. Could the U.S. government's "stick" be used to convert certain signage markets to LED?

But how long will they last?

There's no solid answer to that question. With no moving parts, glass or filaments to break, LEDs are extremely rugged — tough enough for traffic-signal and automotive applications. They won't last forever, but an LED product won't fail with a pop and a flash like an incandescent lamp.

Most LEDs don't fail, they just fade away. Light loss over the years necessitates replacing LED products. The brightness of exit signs and traffic signals is strictly regulated by life-safety building codes. Signage has much looser brightness requirements, and, in some cases, LEDs may be replaced even though they're still operating.

Life ratings, as stated by manufacturers, approach 100,000 hours for red, with less than 20% light loss. New technologies claim those same numbers for all colors — for white, 50,000 hours with less than 30% light loss. That relates to 10 years at 12 burning hours per day.

But these numbers may be conservative! Osram Sylvania advertises life "up to 100,000 hours." Its current models weren't tested over five years, but via manufacturer-laboratory "accelerated life testing," which forces these products to fail more quickly than they would under normal use. On the other hand, a laboratory, with its pristine environment and perfect power quality, is much more forgiving than the real world.

There's no hard proof that today's generation of top-quality, brilliant, energy-efficient LEDs will last 100,000 hours. Come back in five years, and we'll see. Will internal illumination systems for channel letters from Permlight or OSRAM, installed carefully, last 10 years? "Wait and see" is the only answer.

Sign companies have that option. You can wait until the new technology is proven in situ. But frankly, in five years, the competition may have eaten your lunch, or the government may have forced your customers to go elsewhere. The safest bet is to buy top-quality LED lighting systems, and train and supervise installers carefully.

So dive in, and see what your customers think. As sign fabricators prove how profitable the LED channel-letter market can be, the products will become more versatile, with more colors and applications. The industry is in motion, and, like the Jumbotron, new products and markets will arise. Combinations of red, green and blue LEDs mix to create millions of colors, including white light. A standard RGB module might be used to "dial-up" any color a sign fabricator could need. Or, changing color sequences might be programmed, dialed up by the owner at a whim, or even controlled by the retailer's customer.

Quality, white LEDs with good efficiency and life will probably replace many fluorescents and even enable new sign configurations. A channel letter doesn't have to be 6 in. deep any more. By thinking outside the box, new sign construction methods will be based around the new technology. I can't wait to see what you come up with. Osram Sylvania