IEC TR 62728:2011 — Display Technologies: LCD, PDP and OLED — Overview and Differences in Terminology

💡 Key Insight: IEC TR 62728 addresses a fundamental problem in the display industry — the same technical term can mean different things across LCD, plasma, and OLED technologies. This technical report explains these differences, helping engineers, consumers, and standards developers avoid costly misinterpretations when comparing display specifications across different technologies.

1. Background and Scope

IEC TR 62728:2011, prepared by IEC TC 110 (Flat panel display devices), was motivated by a practical problem: as LCD, PDP (plasma), and OLED displays competed in the same markets (particularly television), manufacturers used the same terms — contrast ratio, viewing angle, luminance lifetime — but with different definitions rooted in the unique physical characteristics of each technology. This created confusion for consumers and technical challenges for engineers designing products that incorporate multiple display types.

In 2007, TC110 established a study group with experts from Working Group 2 (LCD), Working Group 4 (PDP), and Working Group 5 (OLED) to harmonize terminology standards or, where harmonization was not possible, to explain the reasons for the differences. The report covers 10 key terms and provides the definitions from each technology standard plus an explanation of why differences exist.

Term	LCD Definition	PDP Definition	OLED Definition
Active area / Screen area	Part of display delimited by picture elements	Maximum image reproducing area	Area with display function on substrate
Addressing	Selecting pixels for activation or deactivation	Setting or changing state with address pulse	N/A (follows LCD approach)
Contrast ratio	Ratio of luminance of brightest to darkest state	Measured with checkerboard pattern (ANS)	Follows LCD approach initially
Viewing angle range	Angular range where contrast ratio ≥ 10:1	Range where luminance variation ≤ 50%	Follows LCD approach
Luminance lifetime	Time to 50% of initial luminance	Not defined (PDP has minimal degradation)	Time from initial to half luminance
Luminous efficacy / efficiency	Luminous flux vs. input power (efficacy)	Separate efficacy and efficiency definitions	Different definitions used

2. Key Terminology Differences Explained

2.1 Contrast Ratio

Perhaps the most debated specification in display marketing, contrast ratio is defined differently across technologies. In LCD standards, it is the ratio of the luminance of the brightest state (white) to the darkest state (black) measured with a full-screen pattern. In the PDP standard (IEC 61988-1), contrast ratio is measured using a checkerboard (ANS) pattern where half the screen is white and half is black simultaneously. This ANS method typically yields lower numbers than the full-screen method because of light leakage from adjacent bright pixels. OLED initially followed the LCD approach, but as OLED technology evolved, measurement methodology continued to be refined.

2.2 Viewing Angle Range

For LCDs, viewing angle range is defined as the angular range where the contrast ratio remains at least 10:1. For PDPs, the criterion is different — the viewing angle range is where the luminance variation from the normal direction does not exceed 50%. This difference reflects the fundamentally different viewing angle physics: LCDs lose contrast off-axis due to birefringence effects, while PDPs are intrinsically Lambertian emitters with minimal contrast variation but potential luminance non-uniformity at extreme angles. OLEDs initially aligned with the LCD definition but may require different criteria for different emission structures.

2.3 Luminance Lifetime

Luminance lifetime is defined consistently across LCD and OLED standards as the time required for the luminance to decrease to 50% of its initial value under specified operating conditions. However, the practical meaning differs: OLED luminance degradation is driven by organic material degradation under electrical stress and is highly dependent on drive current and temperature, while LCD lifetime is primarily limited by the backlight (CCFL or LED), which follows different degradation kinetics. PDPs have minimal luminance degradation over their operating life, so this metric is not typically defined for plasma displays.

✅ Engineering Insight: When comparing display specifications across technologies, never assume that the same term means the same thing. For example, a PDP “contrast ratio” measured by the ANS checkerboard method might be 3,000:1 while an LCD “contrast ratio” measured by the full-screen method might be 5,000:1 — but this does not mean the LCD has inherently better contrast performance. The difference may be entirely due to the measurement methodology. This is the central message of IEC TR 62728.

3. Luminous Efficacy vs. Luminous Efficiency

One of the most interesting terminological distinctions highlighted by the report is between luminous efficacy and luminous efficiency. Both terms describe the conversion of electrical power to visible light, but with different technical meanings:

Luminous efficacy (lm/W) — the ratio of luminous flux to electrical input power. This is an absolute measure of how efficiently a display produces light.
Luminous efficiency — sometimes used as a synonym for efficacy (causing confusion), but more correctly defined as a dimensionless ratio relative to the theoretical maximum efficacy (683 lm/W for photopic vision). In the PDP standard, the two terms are distinguished, while in LCD and early OLED standards, they were used interchangeably — a source of significant confusion that the report aims to clarify.

⚠️ Terminology Alert: Always check which standard a manufacturer is referencing when they quote “efficacy” or “efficiency.” An OLED panel claiming “100 lm/W efficiency” might be referring to the panel-only efficacy (excluding driver losses), while an LCD claiming “100 lm/W efficiency” might be referring to the system efficiency including the backlight but excluding the LCD panel losses. IEC TR 62728 encourages manufacturers to always reference the specific IEC standard and clause number when declaring performance data.

4. Additional Terms Addressed

The report also addresses active area vs. screen area (PDP uses “screen area” to avoid ambiguity with non-active pixels), aspect ratio (linked to the active area definition), quantum efficiency (relevant primarily for OLED where internal and external quantum efficiency are distinguished), and viewing direction (which varies by technology due to different angular emission characteristics).

The approach taken by TC110 — identifying differences, attempting harmonization, and transparently documenting where harmonization was not achieved — serves as a model for other technical committees facing similar cross-technology terminology issues, particularly in rapidly evolving fields where standards developed independently for different technologies converge on common applications.

💡 Future Direction: Since the publication of IEC TR 62728 in 2011, the display market has evolved significantly — PDP has largely been discontinued, while OLED has become dominant in premium applications and LCD remains the volume leader. New technologies such as MicroLED and QD-OLED further complicate terminology. The harmonization approach of this technical report is more relevant than ever as new display technologies enter the market and need to be compared with established technologies using consistent terminology.

5. Frequently Asked Questions

Q1: Why can’t all display technologies use the same terminology?
The fundamental reason is that each display technology has different physical operating principles. LCD uses a backlight with light modulation, PDP uses gas discharge with phosphor conversion, and OLED uses direct electroluminescence from organic materials. These different principles mean that certain measurements that are meaningful for one technology may not be directly applicable to another.

Q2: Is the contrast ratio specification still meaningful for comparing displays?
Yes, but only when the measurement methodology is specified and consistent. IEC TR 62728 recommends that manufacturers specify the standard used (e.g., IEC 61747-1 for LCD, IEC 61988-1 for PDP) and the measurement pattern (full-screen vs. checkerboard). For OLED displays, the contrast ratio is effectively infinite in dark rooms (pixels can be completely off), so the measurement conditions (ambient light level) become the critical specification.

Q3: How has the standard affected modern display specifications?
While PDP has been phased out, the terminology harmonization work of TC110 has influenced how LCD and OLED specifications are reported. Modern display datasheets increasingly reference the specific IEC standard and clause for each declared parameter. The report also laid the groundwork for TC110’s ongoing work on measurement standards for emerging display technologies.

Q4: Are there plans to update the standard for MicroLED displays?
As of the current publication, MicroLED is not specifically addressed, but the methodology established in IEC TR 62728 — identifying differences in terminology and explaining the reasons — can be extended to new technologies as they mature and reach commercial deployment. TC110 continues to monitor emerging display technologies and may develop additional guidance.