Science —

FIPEL wonder-light: Where are the numbers?

World's next great light may now exist, but announcement lacks credibility so far.

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Wake Forest University




However, consult a copy of Carroll's research paper, entitled "Effect of multi-walled carbon nanotubes on electron injection and charge generation in AC field-induced polymer electroluminescence," and it's clear this isn't the case. What Carroll and his research team have done is increased the brightness of a FIPEL light source by adding multi-walled carbon nanotubes (MWNTs).

If anything has been invented, it appears to be an acronym. Research into field-induced polymer electroluminescence out of Seoul's Yonsei University in 2011 instead refers to the technology as FPEL. And that study also investigated the effect of applying carbon nanotubes to the technology. Given the researchers' claims of impressive lifespans hinge on having had one remain in operation for a decade, it's clear that FIPEL has been around for some time.

Fundamentally, though, FIPEL is really a particular example of AC electroluminescence. An electroluminescent material is one that emits light either when transmitting an electric current, or when exposed to an electric field. In FIPEL, a field induced by alternating current causes the electroluminescing material (poly (N-vinylcarbazole) (PVK):fac-tris(2-pheny;pri-dine)iridium(III) [Ir(ppy)3]) to emit light. It's by compositing this material with multi-walled carbon nanotubes that the team claims to have made progress.

Old or new, the researchers make bold claims about the performance of their lights, so Ars asked for the numbers. Unfortunately, Wake Forest declined to provide lumen output or power consumption (from which the efficiency could also be established) of their technology due to "pending publications." They did reveal their lifetimes average 20,000–50,000 hours, which suggests the decade-old FIPEL is either exceptional or turned off from time to time.

Dr. Carroll also revealed that "color rendering index can be customized to any color on the CIE scale desired," rather conflating the color appearance of a light source with its ability to accurately render the color of an object beneath it: related but distinct properties. However, next to light output and efficiency, these characteristics are footnotes.

Though the researchers were coy, the paper itself does provide some clues about FIPEL's performance: "A maximum luminance close to 20 cd/m2 was achieved for Device A without MWNTs in the PVK:Ir(ppy)3 emissive layer. The addition of MWNTs, however, greatly enhanced the luminance of Device A. A maximum luminance of approximately 100 cd/m2 was obtained in the AC FIPEL device with 0.04 wt% MWNTs in the PVK:Ir(ppy)3 emisive layer."

Let's talk units for a moment. Casual watchers of lighting technology may be familiar with the SI unit of luminous flux, the lumen. The lumen output of a light source tells you how much useful light it emits; it's the main performance benchmark. Just as you wouldn't buy a USB hard disk without knowing its storage capacity, you shouldn't buy a light bulb without knowing its lumen output. The term is sometimes expressed as "brightness," though technically this is misleading. Two light sources may emit equal amounts of light, but if one is bigger than the other it will appear less bright because it's emitting less light per unit area.

Enter the cd/m2: a measure of luminance, which is effectively brightness. The candela is the SI unit for luminous intensity: the amount of light emitted by a source in a particular direction. The direction is important because, so far as brightness goes, it doesn't matter how much light is being emitted, just how much of that light is directly entering your eye. The cd/m2 count effectively tells you how much light is coming your way, per unit area of the source.

What the research paper reports is that, by adding just the right proportion of multi-walled carbon nanotubes to a FIPEL light source, its brightness can be boosted by a factor of five to 100 cd/m2.

However, 100 cd/m2 is next to useless. The performance of OLED technology may have some way yet to go, but it has at least breached four figures. A modern, narrow fluorescent tube has a brightness of around 27,000 cd/m2, a 60W light bulb (frosted, at that) 120,000. Even the moon, when full, can boast about 2500 cd/m2. The luminance isn't the whole story, of course: size has to be factored in. Even so, 100 cd/m2 falls way short of the mark. "Not lighting," was how one lighting scientist unaffiliated with this research characterized the luminance to Ars. The 2011 research out of Seoul achieved 350 cd/m2, by the way.

In its favor, nanotube-flavor FIPEL may not be yellow-tinged, buzz, or flicker, but such claims present something of a technological straw man. Thanks to the emergence of triposphor tubes and electronic control gear, fluorescent lighting hasn't suffered from such afflictions for years (or, if it has, it's because something isn't working as it should).

The presence of mercury (albeit in minuscule amounts) is a problem with fluorescent lighting. But if there's an epidemic of CFL light bulb breakages sweeping the nation, Ars has yet to hear of it. In any case, none of these shortcomings can be leveled at the LED, and neither can its dismissal as having a blueish tint. Warm white LEDs have been available for some time.

It isn't news that these problems have been beaten. They've been beaten time and time again over the course of years. If FIPEL does have an advantage over LED, it's the malleability it shares with OLED (though how problematic the lack of malleability of a point source like an LED is up for debate). If it has an advantage over OLED, it may be its long life. None of which has stopped the media from seizing upon the claims of the "advantages" of FIPEL lighting, while neatly overlooking the lack of numbers in the press release.

Ultimately, there may be a very straightforward explanation to the apparent gap in the performance reported in the research paper from hyperbole of the release.

"This is the first in a series of papers. The numbers in paper no. 1 show that the nanotube concept works—which is quite important. However the devices we produce now—reviewed paper is coming out shortly—have achieved 20,000 cd/m2," Carroll told Ars. "We just got in front of publication date of the next three papers (not our fault, it was meant to coincide). They are coming though."

It may be that Wake Forest has cooked up a light every bit as amazing as the reports have led us to believe. For now, though, none of the information released, be it via press release or research paper, contains any specific data to show it. We eagerly await developments, preferably of the specific variety.

Organic Electronics, 2012. DOI: 10.1016/j.orgel.2012.10.017 (About DOIs).

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