New edition of Standard for OLED displays

Measurement conditions and measuring methods for optical and electro-optical parameters to ensure better image quality

By Morand Fachot

The quest for better television pictures has been ongoing ever since TV was invented and in particular after it started reaching a wider audience. The second edition of an International Standard for Organic LED (OLED) displays adds to a series that will contribute to better image quality on these displays.

Flexible OLED screen for smartphone
Flexible OLED screen for mobile phone (Photo: LG)

Constantly improving image quality

From fairly small and fuzzy black and white images displayed on cathode ray tubes (CRT) starting in the 1930s to higher definition (with more lines) black and white and the introduction (starting in the 1960s) of colour, TV pictures never ceased to improve. The development of flat panel displays (FPDs), and of digital television later, marked a watershed. They allowed the broadcast and reception of ever better quality TV pictures. 

Enter high definition

After the introduction, from the mid-2000s of High Definition TV (HDTV), for which the most common format consists of 1080x1920 (horizontal x vertical pixels), or Full HD, the industry is moving to so-called Ultra HDTV (UHDTV) even higher definition, which covers both 4K (3840×2160), or four times as many pixels as HDTV and 8K (7680×4320) 16 times as many pixels as HDTV.

These higher resolutions require better displays. Two display technologies (used also for HDTV) are currently under consideration for UHDTV: liquid crystal displays (LCD) using light-emitting diodes (LED) and Organic LED (OLED).

IEC TC 110: Electronic display devices, develop International Standards for both. 

LED, OLED what’s the difference?

In the back of LCD sets LED backlight shining through liquid crystals covered by red, green or blue (RGB) filters allows (or blocks) light through when activated (or not) by current running through them.

For their part, OLED displays produce images differently. Instead of backlight, colours are produced by organic [carbon-based] compounds that glow when current is applied to them. White OLEDs shining light through sets of RGB filters to create individually coloured pixels.
As each pixel can be shut off when no current is flowing, OLED displays give a deep black, unlike backlit LCD displays. OLED displays can be made very thin and have wide viewing angles, they can also be made can be made transparent as well as on flexible substrates. They are not used only in television sets, but also in a variety of other electronic devices, such as mobile phones. 

IEC International Standards paving the way to better image quality for OLED displays

IEC TC 110 has published nine International Standards for OLED displays in the IEC 62341 series, and is developing more. These Standards define various characteristics, measuring and testing methods for a number of parameters.

Four of these Standards concern measurements relevant to quality aspects, such as image sticking and lifetime, visual quality and ambient performance, and image quality

Also belonging to this category is the latest Standard in the series, IEC 62341-6-1:2017, which “specifies the standard measurement conditions and measuring methods for determining optical and electro-optical parameters of OLED display modules and, where specified, OLED display panels.” These “methods are limited to flat displays measured in a dark room.”

The Standard first gives details of standard measuring equipment and coordinate system, such as light measuring devices and viewing direction coordinate system, as well as measuring conditions, like environmental conditions, power supply, warm-up time, dark-room conditions and standard set-up conditions.

It then lists the various measuring methods of image quality concerning the viewing angle range, cross-talk, i.e. the cross coupling of electrical signals between elements of an OLED display module, observable flicker, static image resolution and moving image resolution.

IEC 62341-6-1 details the various measuring conditions and setup, measurement and evaluation, and reporting provisions necessary to achieve measurements for each aspect.

It contains figures that show examples of the set-ups necessary for measurements, of test signals and graphs of measurements and results.

This second edition of the Standard, available in redline version (RLV) will contribute to ensuring optimal image quality on flat OLED displays.

RLVs provide a quick and easy way to compare all the changes between the Standard and its previous edition. They show changes from previous editions marked in colour.

A RLV is not an official IEC Standard, only the current version of the Standard is to be considered the official document.

Gallery
Curved 4K OLED TV display Curved 4K OLED TV display
Flexible OLED screen for smartphone Flexible OLED screen for mobile phone (Photo: LG)
8K OLED display OLED displays are perfect for 8K content, such as this NHK film