09 · Self-emissive
CRT & the picture painted by a flying electron beam
This is where the series turns a corner. Every screen up to now filtered a backlight. A cathode-ray tube makes its own light, and does it with almost no electronics at all. At the back of a sealed glass vacuum tube, three electron guns fire beams that a magnetic yoke bends across the screen, one line at a time, top to bottom, sixty times a second or more. Where a beam lands it strikes a coat of red, green and blue phosphor, and that spot glows, then fades in a few thousandths of a second. There are no pixels waiting in a grid. The picture is drawn fresh, over and over, by a dot of light moving faster than the eye can follow. It is bulky and heavy and runs hot, yet it still does one thing better than anything that replaced it.
The gun fires a beam straight down the neck. The yoke bends it to aim anywhere on the screen, where it lands on red, green or blue phosphor and makes a glowing dot. Drag the beam, or pick a part to see what it does.
Station 01
How a tube makes color
Three guns, one for red, one for green, one for blue, all aim at the same spot. A thin metal sheet just behind the glass makes sure each beam can only reach its own color of phosphor. There are two ways to cut that sheet, and the choice shapes how the picture looks. Flip between them.
Station 02
The flying spot
There is only ever one lit point on the screen at a time. It races along each line and steps down row by row, and your eye blends the trail into a whole picture. Slow it down to see the single dot, speed it up to watch the image appear.
Station 03
Why motion still looks better
This is the one thing a tube does that no flat panel has matched. Watch the same moving block on a CRT and on a modern panel. The difference is not the refresh rate, it is whether the screen goes dark between frames. Tap to switch.
Station 04
Tube, panel, pixel
CRT was the first self-emissive screen, glowing phosphor with no backlight at all. LCD replaced it with a filtered backlight, and OLED brought self-emissive light back, this time per pixel. Tap a column to see where each one stands.
| Trait | CRT | LCD | OLED |
|---|---|---|---|
| Makes its own light? | Yes, glowing phosphor | No, filtered backlight | Yes, per pixel |
| How the image forms | One beam scans every line | Fixed grid of pixels | Fixed grid of pixels |
| Motion clarity | Best there is | Smears the most | Smears, but fast pixels |
| Black level | Deep | Dark gray | Perfect |
| Input lag | Almost none | Low to high | Low |
| Geometry | Drifts, needs tuning | Perfect, fixed | Perfect, fixed |
| Size & weight | Huge and heavy | Thin and light | Thinnest |
| Burn-in risk | Possible over years | None | Possible over years |
| Still made? | No, ended around 2015 | Yes, everywhere | Yes, premium |
The tradeoff
What the tube nailed, and what sank it
A CRT is a vacuum tube the size of a microwave that draws pictures with a beam of electrons. That sounds primitive, and in some ways it still wins.
Strengths
- Motion clarity no flat panel has matched, because each spot flashes and goes dark instead of holding the frame while your eye moves.
- Almost no input lag, since the beam draws straight from the incoming signal with no buffering or scaling in between.
- It shows any resolution that fits, with no fixed pixel grid to fight, so old game and video formats look the way they were meant to.
Weaknesses
- Enormous and heavy. A big tube needs thick leaded glass to hold a vacuum and block stray X-rays, so a 32 inch set could weigh more than the person carrying it.
- It can flicker at low refresh, draws a lot of power, and the picture drifts out of straight lines and color alignment as it ages.
- Flat screens won on every practical count, thin, light, sharp and cheap, which is why the tube was gone from stores by the mid 2010s.
Questions
CRT, quick answers
Why did CRT TVs and monitors disappear?
Flat panels beat them on everything you notice day to day. LCDs were thin, light, sharp and ran cool, where a tube was deep, heavy and hot and could flicker. Once flat screens got cheap in the 2000s the tube had no room left, and the last consumer CRTs were gone by the mid 2010s.
Are CRTs really better for retro gaming?
For older consoles, yes. There is almost no input lag, the picture is not stretched onto a fixed pixel grid, and the impulse scan keeps fast motion sharp. Light-gun games from that era only work on a CRT at all, since they rely on the timing of the scanning beam.
Shadow mask or aperture grille, which is better?
It depends on what you want. An aperture grille, like Sony's Trinitron, lets more of the beam through, so the picture is brighter with richer color, but you can faintly see the wires that hold the grille steady. A shadow mask is a little dimmer but sharper for text and more stable, since a solid sheet of metal does not need support wires.