How do CRT displays work?

What it is

Three electron guns, one each for red, green and blue, sit in the neck of the tube. Magnetic coils steer the beams across the screen in rows from top to bottom. A mask behind the glass keeps each beam on its own phosphor color. A shadow mask is a metal sheet with tiny holes. An aperture grille, used in Trinitron tubes, is a set of fine vertical wires.

Because the beam draws lines, a CRT has no fixed pixel grid and no processing step between signal and picture. Interlaced video such as 480i draws the odd lines and then the even lines. Progressive video draws every line in order. Many old consoles send 240p, which repeats the same lines every frame, so dark gaps show as scanlines.

Why it matters

• Original look: consoles and computers from the tube era were designed around scanlines and soft edges, and they look as intended on a CRT.
• Light guns: a gun such as the Zapper used for Duck Hunt depends on the exact moment the tube lights the spot it is aimed at. A flat panel processes the picture first and shows it a fraction of a second late, so the gun misses.
• Inputs: check the back of the set. S-Video gives a sharper picture than composite, and RGB, often carried over SCART on European sets, is sharper still.
• Weight and glass: most of the weight is in the front glass, and the glass contains lead. Lift with two people and keep tubes out of the trash.

How this shows up in our work

We collect working CRT televisions and monitors, and we pay for rare professional ones. Details are on our CRT recycling page.

We test sets with real video sources before rehoming them, so a set that leaves us has shown a picture.

Learn more

• Cathode-ray tube on WikipediaTechnical background on tube construction, for readers who want depth.
• Analog television on WikipediaCovers scanning and interlacing, useful for understanding 480i.