Reality Check into LED Claims

Editor’s note: In ST’s 2007 Lighting Survey (see page 102), ST Publisher/Editor Wade Swormstedt reported, “By far, the huge headline is LEDs claiming 30.2% of all sign illumination [which more than doubles last year’s 14.7%, which had been the highest figure to date].” The survey of 2007 lighting activity, reported in 2008, indicates neon’s market has fallen to 22.8%, from a previous year’s stake of 34.1%. The survey respondents said they primarily chose LEDs because of reliability, maintenance and durability.

LEDs have unquestionably attracted huge attention in the signage and display industries. Electronic-digital displays (billboards, large-format outdoor displays and electronic-message centers) presently face few competitive technologies. Equally exciting is the recent shift where more signmakers have migrated to LED-lamped channel letters from neon tubing that dominated this market (as does fluorescent lighting with other, on-premise, illuminated signs) until last year.

The exact breakdown remains elusive, however, because no one counts the total LED-, neon- or fluorescent-lamped sign installations. A survey to determine what existing neon signs (or types of neon-signage applications) are being replaced (or are at risk of being replaced) by LED-lamped signs would be useful. Vendors and buyers could see developing trends and better understand the overall movement. Any analysis must strive to assess LEDs’ true benefits – it should reveal tangible gains and their lasting power.

Why the interest?
LED technology has improved significantly over the past five to 10 years. The lamps’ increased light output allows improved, viable applications, especially for color applications at night. More importantly, experienced LED manufacturers see continuing light-output improvements; LEDs will someday make sense for virtually any lighting application.

Because channel letters and illuminated-sign cabinets are lucrative, future-thinking signmakers should consider practical, alternative light sources that offer long-term cost savings. Many signmakers presently offer LED-based signs as neon replacements to existing customers, but, more importantly, some have successfully acquired new customers who have specified LED-based signs. Further, because LED illumination sources are easily scaled, they’re a better choice for larger channel letters.

Still, these channel-letter makers have also found that changing the light source may affect other constituents – the face color, backing materials and transformer system, for example. In fact, numerous issues should be resolved prior to selecting LEDs: humidity control, temperature dependence and matched bin colors for LED replacement modules, for example.

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Lifespan
Several LED manufacturers quote their 100,000 hours operating lifetimes, but, because channel-letter applications are relatively new, many doubt this claim. These lifetimes, however, derived from two decades of similar, accelerated age and temperature tests, have proved accurate for LEDs and semiconductor lasers employed in the fiber-optic telecommunication fields.

And, although some LED scientists and engineers say their chip’s lifetime could reach 100,000 hours, the luminaire manufacturers should, I believe, conduct further studies and measurements, to demonstrate related elements, such as packaging material and driver electronics, can sustain similarly, particularly in an outdoor environment.

What else?
LED-based display screens, because of brightness and scale, dominate the large-format, electronic digital signage (EDS) display field, but developments and applications evolve. Screen Technology (Cambridge, England) recently introduced a grand-format EDS – the high-resolution, large-format screen ITrans display system, assembled from molded, optical-fiber tiles. ITrans says screen sizes, available in various shapes and sizes, range from 68 to 200 in. diagonal.

The other, common, electronic-display formats – LCD and plasma – are limited in size and brightness, but offer good resolution. At the big-box electronic stores, the LCD and plasma manufacturers offer larger screens, but, for practical reasons, these aren’t likely to reach more than 100-in. diagonal.

Neon
Neon signs have been prevalent for nearly 60 years; the technology is reliable and mature. Neon brightness and efficacies surpass amber, yellow, blue, green and white LEDs. The installed first cost (IFC) is significantly lower for neon, compared to LEDs. And, although some companies may claim otherwise, LED lamps still need time to prove higher performance and comparable or lower cost than neon. Furthermore, neon’s lifespan can reach 100,000 to 200,000 hours, which far exceeds even the highest claims for LEDs.

Neon’s weaknesses are acknowledged – brittleness, some mercury usage, hand processing, a reputation (deserved or not) for fires – and it’s difficult to scale up neon tubing for super-large signs. Nonetheless, it’s well-established and repeatable manufacturing process has a vast crowd of devotees.

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When neon was the sole, unquestionable choice – and energy consumption wasn’t an issue – keen measurements and comparison weren’t crucial. Now, LED and neon users should understand lighting’s important parameters and how they’re measured. I believe the sign industry should work to establish comparison methods, so signmakers can evaluate the different technologies. Such a project would include glossaries and application advisories, giving real scenarios that promote the best technology usage.

Why do red LEDs out perform neon for cost, brightness and efficacy? Krypton Neon’s (Long Island City, NY) website (www.neonshop.com) displays an excellent comparative chart, although it dates back to 2004. Under the Tech Spec header, the Comparison Tables show red neon produces 25 lumens per watt, whereas red LEDs provide 38.

This gain relates to with internal quantum efficiency (IQE), which is the highest for red compared to other colors. Inherently, IQE is nearly twice ( roughly 100%) for red LEDs than for blue LEDs (roughly 50%). IQE yields the amount of light converted from a unit of injected current via electroluminescence.

What also matters is external quantum efficiency (EQE), which determines the actual light extracted from the LED module. EQE depends on reflection caused by the refractive-index mismatch between the air/encapsulation medium and the semiconductor chip. This index matching, and other surface-roughening techniques that reduce reflection, must be incorporated into the module, to increase LEDs’ overall efficacy (lumen/W).

Future LED applications in channel letters and cabinet signs are bright, but several years may pass before LEDs become a genuine threat to neon. Although some manufacturers currently use white LEDs in some channel letters and other backlit-sign applications, mainstream adoption of white LED technology requires cost and performance improvements. White LEDs are the most difficult to manufacture and they’re still not par with neon. Additional signage applications – medium and large – will spawn from improved, white LEDs.

Concepts
A physics degree isn’t necessary for buying and utilizing LEDs, but some understanding of principles and theories is important, especially the meanings of such parameters as lumen, candle, efficacy, luminance and illuminance. Also, signmakers need better understanding of their interrelations when using them for relevant measurements.

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In addition, if you compare LED light-output measurements against other light sources, remember that LEDs have different horizontal and vertical beam angles and, due to an inherent narrowness, a unique beam pattern. These aspects can affect comparisons over a particular space.

The future
Keen observers say the sign industry stands at the dawn of the EDS era. It’s possible, too, that various other display technologies will continue, on an even broader scalability range. Still, LEDs will continue to play a very significant role in signage, whether for display screens or as an illumination source.

Today, more than ever, sign companies are offering LED-based channel letters. Well-recognized suppliers SloanLED (Ventura, CA), GE Lumination (Cleveland, OH), and ElectraLED (Largo, FL) are a few in the LED channel-letter market. The demand for LEDs in channel-letter applications is growing and will grow further. (Some manufacturers now ship their channel-letter LED products in reels, so that fabricators can cut lamp strips to size, on premise.) With such flexibility, and even better consistency, LED-based sign manufacturers can easily plan for future growth.