CRTs: How a TV Works

At some point most of us have wondered: How does a TV or a computer monitor display images?

Screens on these devices usually have either a liquid crystal display (LCD), a plasma display, or a cathode ray tube (CRT). CRTs are the most common way to display pictures—you probably think of them as the older, “bulkier” style of televisions or computer monitors.

So how does a CRT work?

Image Credit: HowStuffWorks

A CRT has two terminals—a positively-charged “anode” and a negatively-charged “cathode.”

The cathode is a heated metal wire (filament) inside of an electron tube. A ray of electrons pours off the heated cathode into a vacuum. Because opposites attract, the anode then pulls in the negatively-charged electrons away from the cathode. One of the anodes focuses the electron beam and the other one accelerates it.

The beams fly through the vacuum that is located inside the tube and hit the flat, phosphor-coated screen on the other side (phosphor is what makes the TV or monitor glow). There is also a coating inside the tube that picks up the electrons that accumulate near the screen.

The electrons are controlled via a system of coiled wires. These create a magnetic field that steers the electrons. One set moves them vertically and the other horizontally. By controlling the voltages inside the coil, you can control where the electron beam ends up. An image is produced by controlling the intensity of three electron beams—one for each additive primary color (red, green, and blue). A video signal is used for reference.

Why are CRTs dangerous?

CRTs can contain as much as eight pounds of lead per unit, making them one of the most difficult types of e-waste to recycle, as well as one of the most important types to recycle responsibly. Not only do they contain lead, but also high levels of phosphorous and cadmium.

Although some companies charge a fee to dispose of CRTs, All Green Electronics Recycling will do so for free.

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