The Ultimate Limit: -40 Degrees
-35 degrees Celsius / -31 ⁰F proved to be the ultimate limit for smart phones. Even the most persistent one, Samsung Galaxy S II, shut down when we tried to use the phone.
None of the tested touchscreen smartphones could stand such extreme conditions. But, perhaps surprisingly, some feature phones did work, even though their LCD displays showed serious slowness. But when the temperature dropped to -40⁰C / -40⁰F, none survived. Even the toughest ones shut down.
Out of the 18 phones we tested, only two feature phones could survive until these temperatures: a very cheap Nokia C1-01 and a five-year-old Nokia E65, which was one of the devices chosen for comparison. In the end, the Finnish engineers did design the best mobile phones for sub-zero environments. They may not be equipped with high-end touch-screens, but they work! And it's probably not a surprise: the coldest temperature in Finland peaks at -40 degrees almost every winter.
Blame the Battery
When the temperature drops enough, a cell phone thinks that its battery is empty -- even if it's fully recharged -- and shuts down.
A chemical reaction takes place inside the battery. The product of the reaction is electrons, and the flow of electrons creates an electric current which the cell phone uses as its source of power. The speed of this reaction depends on the temperature: the colder it gets, the slower the reaction, and the smaller the current that the battery can provide.
The voltage of the battery isn't stable, either. The nominal voltage of a lithium-ion battery is typically 3.7 volts, but in reality the voltage is between 2.7 V (empty battery) and 4.2 V (fully charged battery).
In cold temperatures the internal resistance of the battery grows, causing the output voltage to drop. When the voltage drops too low, below a threshold voltage, the cell phone thinks the battery is empty -- even it is fully recharged -- and shuts down.
How the Cold Affects Different Displays
An LCD display consists of layers. The actual liquid crystals are positioned between the polarizing filters and electrodes. A TFT layer (thin film transistor) is positioned behind the screen to control the pixels of the screen.
When the temperature drops, the viscosity of the liquid crystal material grows exponentially. Depending on the material used in the liquid crystals, the viscosity grows 2-3 times larger when the temperature drops 10 degrees Celsius (18 degrees Fahrenheit). This means the pixel changes its color slower in the cold.
When it's cold enough, the pixel acts so slow that it can't change its color fully before the next frame is already drawn on the screen. This is when the display seems to work slowly and ghosting or image blur appears on the screen.
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