Liquid Crystal Displays

Staring at a screen? We are. But what kind of screen?

Sadly, not the silver screen (it would take too much film). But there are computer screens (and television screens) that have what’s known as a liquid-crystal display, or LCD for short. LCDs use concepts related to electric fields to do their magic. We’ve been using LCDs for years in calculators and watches, but these days we use them in color to full advantage.

Liquid crystals are, as their name implies, part solid and part liquid. Each point of display It’s a bunch of tiny crystals in a fluid, in a random orientation. When an electric field is applied, however, the crystals align.

Rotating the liquid crystals changes the light polarization, which changes the image, which is pretty cool. We’ve read, an electric dipole consists of two opposite charges of equal magnitude. The liquid crystals act as dipoles. When placed in an electric field, the dipole experiences a torque which aligns it with the E field. By applying an external electric field, we rotate these crystals as we see fit and alter their optical properties. And that’s how we get to watch the original Star Wars films with incredible detail.

It’s not just spinning crystals and electric fields. LCD screens require the help of polarization filters, which either transmit or block the light depending on the crystals’ orientation. Think of polarization filters like blinds covering a window: if the crystals are aligned perpendicularly to the E field in the light, then no light can pass. Several techniques may then used to produce different colors of images, allowing us to look at pictures on our screens in color.