FROM THE BENCH
FROM THE BENCH
DUAL-LAYER TV SCREENS The latest form of LCD display is the best yet, says Alan Bennett
S
ince the demise of plasma TV screens in 2014 there have been two basic direct-view display technologies: LCD and OLED. Each has its pros and cons.
Megacon screen layers
RESTRICTIONS Both LCD and OLED displays can be made in large sizes and with very high definition. LCD is by far the most common type, used with an LED backlight. It gives the highest brightness levels, especially in the more expensive QLED and Quantum Dot forms. Its drawback is that even when its LCD light shutters are fully turned off there is slight leakage of illumination through them so that a true black cannot be achieved, though it can be reduced by ‘local’ and full-field dimming of the backlight. “Viewing OLED screens, because in high ambient each pixel is self-emissive, light requires a bright can achieve a true over its full area. In screen display, and to black: each diode can effect the inner layer fully exploit HDR (High be fully turned off. The produces the black drawback here is that and white (luminance) Dynamic Range) systems, they are unable to reach component of the good black level and to a very high brightness picture while the outer a high brightness level – driving them one provides the colour. capability are too hard reduces their It is very effective, but needed.” operational life. Viewing in expensive to produce. high ambient light requires a PANASONIC MEGACON bright screen display, and to fully Exhibited at IFA 2019 was Panasonic’s exploit HDR (High Dynamic Range) Megacon (Mega contrast) prototype, a 55 inch systems, good black level and a high brightness UHD screen with dual-layer technology. Both capability are needed. Micro-LED screens (see its LCD screen layers have UHD/4K definition our August 2019 edition, page 19) can achieve so that individual pixels can be blacked out both but are not yet available in economic or without any effect on adjacent ones. This is a mass-market form. huge advantage over even the ‘tightest’ local DUAL-LAYER LCD dimming systems, in which the limited number Dual- layer screens are based on LCD of LED backlight clusters causes whole bunches technology, in which polarised light is ‘twisted’ of pixels to be darkened. The Megacon has in a multi-point liquid crystal display panel so a claimed contrast ratio of 1,000,000:1, with that it is blocked by a downstream polarising a maximum brightness of 1000 nits, the level filter working at right-angles to the first. It is not currently achieved by top-end conventional fully effective, and the brighter the backlight the LCD/LED screens with QLED and Quantum Dot more light leakage occurs. Dynamic local and technology. A wide angle of view is another overall dimming of the backlight – incorporated attribute, according to Panasonic. This screen, in more expensive models – helps, but is not as exhibited at IFA, is several centimetres thick, targeted tightly enough to completely eliminate and at present likely to find a role as a top-level light bleed and blooming effects in the image. A studio reference monitor at a price expected dual-layer screen has a second LCD array behind to be in the tens of thousands of pounds. It is the main one; their pixels are aligned so that what not yet envisaged for the home cinema market, little light escapes through a fully turned off rear but all such innovations have the potential to pixel is intercepted by the outer one, reducing appear there in the fullness of time; it will need the black level to virtually zero, comparable to to slim down, perhaps physically and certainly that of an OLED screen. The white LED backlight price-wise, even to become a niche model for can be very bright and uniform in intensity well-heeled movie enthusiasts in the future...
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JAN/FEB 2020
HISENSE U9E Also featured at IFA 2019 (and already launched in China) was the Hisense duallayer TV model, expected here this year at a price comparable with currently available high-end TVs. It’s not up to the standard of the Panasonic Megacon! This 65-incher has a UHD outer screen layer but the inner one is coarser at 1080p definition, providing one LCD lightblocking cell for each four pixels in the image. This does not impinge on the UHD resolution as viewed, but provides less tight targeting, so to speak, and hence a contrast ratio around 150,000:1, aided by a new low-reflection outer surface. It can, however, produce a peak brightness of almost 3000 nits. In terms of brightness, then, it is way ahead of all conventional TV screens and second only to the emerging Micro-LED type (August issue, page 19). This is more than adequate for all home cinema needs. In assimilating these brightness levels bear in mind that an LCDbased screen can achieve its peak level over the whole image area when required, while OLED ones can only manage their quoted top level over a smaller area of the picture. Dual-layer screens, especially of the sort developed by Panasonic, will be highly priced but our industry thrives on innovation: remember that when colour TV started, and again at the launch of thin-screen TVs the sets were unaffordable for most people. Now mass-production, competition between manufacturers and world-wide research, production, manufacture and marketing are driving prices down as never before, though not always to the advantage of the retailer...
