Full Disclosure: LG Display is a client of mine at the time of this writing. There has been some confusion in the market regarding the company’s M+ technology and at the request of LG Display I have written this article for clarification. This article has been edited only by me.
What is M+?
M+ is LG Display’s sub-pixel panel technology that uses four sub-pixels rather than three. Most displays use three sub-pixels: red, green, and blue. This RGB sub-pixel arrangement in a 3×1 layout is often referred to as RGB stripe. Three sub-pixels make a single pixel, physically and visually. M+ on the other hand uses four sub-pixels: red, green, blue, and white, or RGBW. And a pixel can have a different mix of RGBW.
For instance, the first pixel in a M+ panel starts off with RGB, and the next one to the right is WRG, and then BWR, GBW, etc. The diagram in this PDF (LG Display Addresses Environmental Issues with M+) should help with visualizing the structure.
The benefits of adding a white sub-pixel are brightness and cost. Right now as I am writing this article on WordPress roughly 90% of my screen — a 15.4″ 1920×1200 LCD — is white, which means light is passing through all three sub-pxiels; remember all three primary colors (red, green, and blue) are required to make white. Pushing photons through a RGB color filter is inefficient; about 60-70% of light gets blocked. The light transmittance rate further declines when more pixels are added to the same screen. The trend going from 1080p (1920×1080) to 4K/UHD (4096×2160/3840×2160) is a good example.
Light is generated by a backlight. Roughly speaking, a 10,000 cd/m2 LED backlight will result in a 500 cd/m2 screen. That translates to a 5% light transmittance rate. It doesn’t help that the backlight is the most expensive component of a LCD.
The transition from 1080p to 4K/UHD adds a lot of pixels. A 1080p set will sport a 1920×1080 pixel format for a total of 2,073,600 pixels. A 4K/UHD set has 8,847,360 pixels (4096×2160) or 8,294,400 pixels (3840×2160). That’s more than quadruple the number of pixels, and puts pressure on the backlight to generate enough light.
M+ is the result of the transition to 4K/UHD and the need to reduce the cost related to the backlight to bring to market affordable 4K TVs. The addition of a white sub-pixel improves the light transmittance rate to 8%. Assume the same brightness target of say 1000 cd/m2 on a 4K/UHD TV, M+ translates to lower backlight costs by reducing the number of LEDs and/or optical films compared to a panel that uses a RGB stripe configuration.
Skyworth, Konka, Hisense, Haier, Xiamoi, and Philips are using LG Display’s M+ LCD panels for their 4K/UHD TV lineup. I expect 4K/UHD TV prices to continue falling, and at some point — US$499 50-inch 4K/UHD? — prices will hit an inflection point, from which there will be mass adoption.
Is M+ 4K/UHD real 4K/UHD?
This is the question that requires some clarification. Let’s compare four pixels in a row. On a M+ panel the four pixels would be made of these four sub-pixel sets: RGB, WRG, BWR, GBW. On a RGB stripe it would be: RGB, RGB, RGB, RGB. Now let’s count the sub-pixels:
- M+: R (3), G (3), B (3), W (3)
- RGB Stripe: R (4), G (4), B (4)
RGB has a total of 12 sub-pixels. The composition of the sub-pixels are different, but the total number of sub-pixels in the M+ example is also 12. The white sub-pixel is also a sub-pixel though its purpose is slightly different.
When the screen is mostly white, like my screen at the moment, the white pixels are used to make it brighter without using more power. The white sub-pixel also increases the difference in brightness between pixels to enhance image sharpness.
The United Kingdom’s Intertek, Germany’s TÜV (Technischer Überwachungsverein), China’s CESI (China Electronics Standardization Institute), and the United States’ UL organizations have certified LG Display’s 4K/UHD M+ as real 4K/UHD.
I don’t blindly trust international organizations, but the ones mentioned above have some credibility. I highly recommend taking a look for yourself. The most important question should be: How does a 4K/UHD TV using a M+ panel look to you?