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LCD brightness, or more technically “Luminance”, is measured in millicandles of luminance per square meter, also known as “NITs”. Serious specifies a “minimum typical” brightness for each display, meaning that the described LCD has a typical luminance specification at least that amount. LCD brightness is measured at the LCD’s initial power-up. See backlight longevity, below, for how LCD backlights degrade over time.
As a simple rule of thumb:
Luminance and Luminance Uniformity is calculated based on 9 measurements as follows:
LCD backlight lifetime is a function of the specific LEDs selected for the backlight, and is measured in thousands of hours. If the backlight is maintained at 100% full power from initial LCD powerup fresh from the Serious factory, the typical brightness after that many hours will be typically 50% of its initial luminance.
Some common backlight longevity specifications are:
The technical definition of the test condition is as follows: The final brightness is at 50% of original brightness with an environment of ambient air flow at Ta=25±2C,60%RH±5% with LED forward current (If) at the recommended typical for maximum desired brightness.
Color LCDs get darker when operated below the minimum temperature range, and respond more sluggishly to visual changes. At higher temperatures, LCDs get washed out. At certain temperature extremes, the LCD driver chips may not function at all. The LCD temperature range is the minimum range where the LCD is deemed to perform acceptably without factoring in any backlight warming. LCD backlights do generate (when fully powered) several degrees of heat that can help obtain better LCD functionality at the low end of the LCD specification.
Note this range does not mean the SIM will cease functioning necessarily. Most SIMs are rated at -40 to +80C, so it is possible the SIM can continue to function even if the LCD is not visible to the user.
This is the number of bits the LCD uses to represent one pixel. There is often a GUI performance penalty for going above 16 bits because 4 bytes (vs. 2) have to be used to represent a pixel on the driver MCU and typically this impacts memory and performance (or, alternatively, the power of the MCU required to deliver equivalent performance). Unless your GUI has extensive large shading gradients, 16-bit is almost always adequate for most applications.
LCD technology is rapidly evolving. There are several types of “viewing technology” now available. Some are a function of the raw LCD panel fabrication process, others a result of optically bonded film techniques.
Viewing angle is a set of 4 measurements based on the 4 directions of deflection from straight-on viewing:
A typical capacitive touch LCD is dimensioned similar to this drawing:
The terms on this drawing are as follows:
Response time is the time for a display pixel to turn on or turn off. Specifically it is the slower of Tr and Tf, where:
As measured by a LCD-5100 luminance measuring device or equivalent.
Note that the specification of Response Time is at 25C; response times will often be progressively slower as the operating temperature drops below -10C for most panels.
There are two types of interpretations of Tr and Tf, depending on the nature of the panel technology: Normally Black (Negative) or Normally White (Positive).
Normally Black type, or “Negative”, displays include IPS type panel technologies.
Normally White type, or “Positive”, displays are the most common and include standard TN-TFT display technologies.
Contrast ratio is the ratio between the display pixel fully white to the display pixel fully black:
The measurement conditions are:
Most TN-TFT displays have typical contrast ratios in the 250:1 to 400:1 range and occasionally as high as 600:1.
IPS displays typically have higher contrast ratios, often 600 to 800:1.
Color can be technically and empirically measured, but how it is perceived by the human eye is the true goal of color appearance in an LCD. A color “gamut” is a specific range of color out of the full color palette most relevant to how the human eye perceives color.
While there are many methods used to show a color gamut, the industry standard for displays is the CIE 1931 Chromaticity XY Graph:
This diagram shows the “standard” color spaces we want to reference when we talk about what color appearance can be generated by a specific LCD:
Because the NTSC gamut is the most relevant color space to the human eye, the standard mechanism for determining an LCD’s color performance is to compare the LCD’s performance (the dashed triangle) against this NTSC gamut:
Most industrial LCDs have a typical NTSC% of approximately 50-52%.
© 2023 Serious Integrated, Inc. All rights reserved.
