- Resistive touch: inexpensive, robust, and suitable for most conditions including gloved and wet
- No touch: inexpensive, can be put behind polycarbonate or cover glass for very harsh environments
- Capacitive: for higher end applications with bare finger and dry conditions; newer capacitive touch technologies are more resilient to small amounts of water or even food service or medical gloves.
LCD brightness 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.
- 200-399 NITs: good for almost all indoor environments, outdoor possible but may need shrouding to prevent bright sun
- 400-699 NITs: excellent for all indoor environments, considered mostly sunlight readable when not in direct sun
- 700-999 NITs: considered sunlight readable, some washout in direct sun
- 1000+ NITs: sunlight readable, direct sun readable
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 (at 25C) from initial LCD powerup fresh from the Serious factory, the typical brightness after that many hours will be typically 50% of its initial luminance.
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.
- -20 to +70C: most cost effective, most common
- -30 to +70 or 80C: harder to obtain, premium product
- -40: nearly impossible to buy LCDs rated at -40, typically requires heater modules which are expensive and require ~1W per square inch to power
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.
- 16 bit / 65K colors: most cost effective, most widely available, suitable for most applications (RGB565)
- 18 bit / 262K colors: cost effective, adds slightly better Red/Blue (RGB666)
- 24 bit / 16M colors: excellent gradient support (RGB888 or YUV422), sometimes a price premium, MCU memory/performance implications
Viewing Angle and TEchnology
LCD technology is rapidly evolving. There are several types of “viewing technology” now available. Some are a function of the raw LCD glass fabrication process, others a result of optically bonded techniques. Viewing angle is measured based on the 4 directions of deflection from straight-on viewing like this:
- Landscape: traditional landscape mode viewing. When the LCD is viewed with the long edge horizontally, has good viewing from 3 sides (typically 9, 12, and 3 o’clock) and reduced angle viewing from one (typically 6 o’clock)
- Portrait: traditional portrait mode viewing. When the LCD is viewed with the long edge vertically, has good viewing from 3 sides (typically 9, 12, and 3 o’clock) and reduced angle viewing from one (typically 6 o’clock)
- Multi Viewing Angle: Multi-domain Vertical Alignment (MVA), often mis-called “Multi Viewing Angle” is a new technology combining optics with LCD manufacturing technique providing very good viewing angles from all 4 directions without contrast or color shifting. MVA carries a slightly price premium and, while less common than traditional LCD technology today, is becoming more available in more sizes
- In Plane Switching (IPS): an LCD fabrication technology which gives excellent viewing angles from all directions without contrast/color shift. It carries a higher price premimum and uncommon today in the industrial/embedded space, but is anticipated to become more available in 2016+
- Organic LED (OLED): virtually unavailable in the industrial/embedded market; no indication yet when it will become available and cost effective