In a tightly reasoned article on Peter Palomaki’s blog last week, Palomaki (who I will now call Sherlock Holmes) and collaborator Matt Bertram (Dr. Watson) convincingly argue that LG’s “Nano Cell” LCD-TV technology is nothing more than a red dye absorber laminated to the display’s front polarizer.
Check here for the article link.
Palomaki objects to calling the dye particles “nanoparticles” since that designation is properly reserved for nanoscale crystalline particles. LG asserts that their particles are one to two nanometers in diameter.
LG Electronics (the TV maker) and LG Display (the panel maker) have been very disciplined in not describing the technology in meaningful detail. On more than one occasion, LGD has told me and other analysts than the technology, which LGE calls “Nano Cell” and which LGD calls “IPS Nanocolor I,” consists of nanoparticles applied to the front polarizer, and that the layer acts a color filter that improves color purity. They also suggest, although don’t say so directly, that the layer substantially improves the viewing angle. When asked the key question, how can a nanoparticle layer serve as a color filter, a variety of LGD staffers have said they’re not sure or refuse to answer.
A Puzzle to Solve
But now, Holmes and Watson have supplied the answer: This is a conventional organic color filter, regardless of the size of the molecules. In fact, said Bertram, they have identifyed the dye as ABS 594 and the manufacturer as Exciton, which was acquired in 2016 by eyeglass giant, Luxottica. ABS 594 was originally developed to make the reds in plasma display more red and less orange, Bertram said, and repurposed it for the TV application. (I remember the representative of a plasma company proudly describing this technology to me back when plasma was king for flat-panel TVs.)
But let’s take a step back. One of the problems in conventional LCD television is that the light source is a number of white LEDs, each of which is actually a blue LED with broad-band YAG yellow phosphor inside the LED package. The broad-band yellow contains red and green light, but the intensities of the red and green are weak and the spectra are not optimal for the red-green-blue matrix color filter that gives each sub-pixel its appropriate color. The result is a limited color gamut, limited peak luminance, and problems with color purity. Like those old pre-ABS 594 plasma displays, the reds on a conventional LCD are quite orange.
There are several ways of addressing these issues, including quantum dots (superbly effective and releatively expensive at the moment) and incorporating red and green narrow-band phosphors inside the LED package instead of YAG (pretty darn effective and moderately expensive). (For more on this topic see There’s More than One Way to Make a WCG LCD – Man. Ed.)
You can also avoid the problem entirely by using self-luminous sub-pixels, as is the case with OLEDs (expensive for now). It is now clear that LG’s approach should be a relatively inexpensive way of blocking a narrow band of wavelengths between the red and green spectra, thus improving color purity and increasing color gamut. However, the approach does nothing to improve luminance and could reduce luminous efficiency. (LGD denies that it reduces efficiency, and that may well be true.)
Where’s the Evidence?
But how did Palomaki and Bertram figure out what LG is doing? They began by buying an LG 55SJ85000 Nano Cell TV and measured with a spectrophotometer the spectra of “white” in front of the screen and at the diffusor film (before the color filters). From these measurements, Holmes and Watson determined that the light source were indeed the familar “white” LEDs.
When they looked at the spectra of individual colors, the green spectrum had an odd depression on the right-hand side (Fig. 1), which Palomaki thought might be a signature that could be matched to known absorbers, but there are a lot of absorbers. The team did a patent search and found that LG Chemical had filed a patent application describing the application of narrow-band absorbing dye complexes in displays. The patent listed a number of molecular absorbers suitable for the application. The team identified two of these absorbers that have optical spectra that fit their measurements. Of these, the ABS 594 dye also has the depression in the spectrum shown in Fig. 1.
The team then modeled various combinations and compared them with the spectra measured for the LGE Nano Cell TV. The model for the system incorporating ABS 594 is a virtually perfect match for the spectra from the TV. The team did further modeling to compare the gamuts of LCD-TVs using narrow-spectrum phosphors, quantum dots, and white-LED LCD-TVs with and without the absorbing filter. The filter significantly improves the gamut of the white-LED LCD-TV, but its gamut is meaningfully smaller than TVs using the narrow-phosphor approach, and smaller yet when compared with a quantum-dot-enhanced LCD-TV.
Conclusion: LG’s Nano Cell technology is a low-cost approach to meaningfully improving the color purity and color gamut of LCD-TVs, but it is less effective than the competing (and more expensive) technologies for premium LCD-TVs. I will speculate that LGE and LGD are well aware of this, because “IPS Nanocollor II” will be introduced this year or next. LGD is not saying too much about this replacement technology, except that it has green and red “nanoparticles in a layer beneath the LCD sandwich. LGD said these particles will not be quantum dots, so I will speculate that they are phosphors.
Case closed thanks to Palomaki and Bertram. “Elementary, my dear Watson.” – Ken Werner
Ken Werner is Principal of Nutmeg Consultants, specializing in the display industry, manufacturing, technology, and applications, including mobile devices, automotive, and television. He consults for attorneys, investment analysts, and companies re-positioning themselves within the display industry or using displays in their products. He is the 2017 recipient of the Society for Information Display’s Lewis and Beatrice Winner Award. You can reach him at [email protected]