How Does Temperature Affect LCD Displays on Calculators?
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LCD Displays Use Liquids
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The display in most calculators uses passive LCD, an abbreviation for "Liquid Crystal Display." These displays incorporate special LCD fluid in a glass container with reactive coatings on the inside surface. When a circuit board designed to drive the calculator's display fires, it excites the LCD fluid and causes it to react with the coating inside the glass container. Depending on the calculator, this process may take place as the display changes, on a predetermined periodic refresh rate, or as is common; in high end devices and newer calculators.
High Temperatures Affect the Display
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Because LCD fluid must be easily excited by the spark of a printed circuit board, it is designed to quickly react to high temperatures. Just as the high temperature of the circuit spark causes the fluid to expand and interact with the reactive coating, high ambient temperatures also cause the fluid to expand and react. A calculator left in direct sunlight (where it absorbs ultraviolet radiation) or in a hot car (where the intense heat excites the LCD fluid) will likely display a black screen; this display is a result of the hot, excited LCD fluid expanding and interacting with the reactive coating across the entire display.
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Cold Temperatures Also Affect the Display
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While hot temperatures cause the LCD fluid to expand and react with the display coating, the opposite effect takes place after exposure to very cold ambient temperatures. Cold temperatures, like those experienced when the calculator is left in a car during a cold winter night or accidentally stored in a refrigerator, cause the LCD fluid to contract and respond more slowly to heat stimulus. When cold LCD fluid is exposed to a spark from the printed circuit board, it may take longer to expand and react with the display coating. After a few moments of use, though, the fluid tends to return to normal operation as it absorbs the user's body heat.
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