Backlit vs. Reflective
Note that our simple LCD required an external light source. Liquid crystal materials emit no light of their own. Small and inexpensive LCDs are often reflective, which means to display anything they must reflect light from external light sources. Look at an LCD watch: The numbers appear where small electrodes charge the liquid crystals and make the layers untwist so that light is not transmitting through the polarized film.
Most computer displays are lit with built-in fluorescent tubes
above, beside and sometimes behind the LCD. A white diffusion panel
behind the LCD redirects and scatters the light evenly to ensure a
uniform display. On its way through filters, liquid crystal layers and
electrode layers, a lot of this light is lost -- often more than half!
LCD History
Today, LCDs are everywhere we look, but they didn't sprout up
overnight. It took a long time to get from the discovery of liquid
crystals to the multitude of LCD applications we now enjoy. Liquid
crystals were first discovered in 1888, by Austrian botanist Friedrich Reinitzer. Reinitzer observed that when he melted a curious cholesterol-like substance (cholesteryl benzoate),
it first became a cloudy liquid and then cleared up as its temperature
rose. Upon cooling, the liquid turned blue before finally
crystallizing. Eighty years passed before RCA made the first
experimental LCD in 1968. Since then, LCD manufacturers have steadily
developed ingenious variations and improvements on the technology,
taking the LCD to amazing levels of technical complexity. And there is
every indication that we will continue to enjoy new LCD developments in
the future!
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In our example, we had a common electrode plane and a single electrode bar that controlled which liquid crystals responded to an electric charge. If you take the layer that contains the single electrode and add a few more, you can begin to build more sophisticated displays.
Common-plane-based LCDs are good for simple displays that need to show the same information over and over again. Watches and microwave timers fall into this category. Although the hexagonal bar shape illustrated previously is the most common form of electrode arrangement in such devices, almost any shape is possible. Just take a look at some inexpensive handheld games: Playing cards, aliens, fish and slot machines are just some of the electrode shapes you'll see.
