Most LCDs today also use a source of light coming from the rear of the display (backlight), such as a fluorescent light, to make the liquid crystal appear darker against the screen when in its cloudy phase. LCD makers also use sheets of polarizer material to enhance this effect.
The Symbol MC9100, MC9190 LCD screen
and keypad module gives you a handy 53 keys display, 5 buttons and a controllable backlight, plug it straight in on top of your handheld computer board or other project shields. The display is set behind the shield for a low profile fitment and nice look and we've included panel mounting screw holes in the corners.
Some LCD screens are advertised with a contrast range of 1000:1, which is 10 stops, but that is under ideal conditions, which never occur in practice. Of course, if you are in very dim light, the eye will produce visual purple over a 10-15 minute adaptation time to increase its sensitivity (but not its DR) by several stops. Added all up, the eye system is capable of over 14 stops of DR, but that's cheating somewhat.
The basis of LCD screen technology
is the liquid crystal, a substance made of complicated molecules. Like water, liquid crystals are solid at low temperatures. Also like water, they melt as you heat them. But when ice melts, it changes into a clear, easily flowing liquid. Liquid crystals, however, change into a cloudy liquid very different from liquids like water, alcohol, or cooking oil. At slightly higher temperatures, the cloudiness disappears, and they look much like any other liquid.