Quick answer: A CRT (cathode-ray tube) television draws a picture by firing a beam of electrons at a glass screen coated with glowing phosphors. Magnetic fields steer the beam across the screen line by line, many times per second, and your eyes blend those glowing lines into a moving image. That process is what creates the scanlines, soft edges and glow that define the retro TV look.
Understanding how the tube works makes it much easier to appreciate real vintage sets and to judge whether a retro TV simulator is imitating the right details. This guide walks through the technology in plain language, from the electron gun to the static between channels.
The cathode-ray tube in one minute
A CRT is a large, sealed glass tube with most of the air removed. At the narrow back sits an electron gun, which heats a cathode so that it releases a stream of electrons. High voltage accelerates those electrons forward, and they strike the inside of the wide front of the tube, the screen. The screen is coated with phosphors, materials that glow briefly when electrons hit them.
Color sets use three electron beams, one for each primary color, and three kinds of phosphor dots or stripes: red, green and blue. By varying the strength of each beam, the set mixes millions of shades. Monochrome sets from the early decades used a single beam and a single phosphor, which is why those pictures are black and white or tinted slightly green, amber or blue.
How the beam draws a picture
Electrons cannot be aimed with a lens, so a CRT bends them with magnetic fields. Coils around the neck of the tube, called the deflection yoke, push the beam horizontally and vertically. The beam sweeps from left to right, flies back, drops down a little and sweeps again. When it reaches the bottom it jumps back to the top and repeats.
Each sweep is a scanline. A full pass of lines is a field, and the repeated passes happen so fast that the screen appears to show a steady moving picture. The brightness of the beam during each sweep decides how bright each point on that line will be.
Scanlines, resolution and interlacing
Television standards fixed how many lines make up the picture. The North American analog standard, usually called NTSC, uses 525 lines in total with roughly 480 visible, while many other regions used 625-line PAL or SECAM systems. Because lines are physical, a CRT does not have fixed square pixels in the way a modern flat panel does.
To save bandwidth, broadcast television used interlacing. Instead of drawing every line in order, the set draws the odd lines in one field and the even lines in the next. In NTSC regions that means about sixty fields per second, which combine into roughly thirty full frames. In 50 Hz regions the field rate is about fifty. Interlacing is one reason fast motion on old broadcasts can look slightly combed or flickery when displayed on a modern screen without correction.
Console games from the same period often used a trick called 240p, drawing the same set of lines in every field instead of alternating. The dark gaps between lines then stay in the same place, which produces the very visible scanline pattern many retro gamers love.
Why phosphors glow and blur
When electrons strike a phosphor it lights up, then fades over a short time. This fade is called persistence. It helps smooth the image and hides flicker, but it also means bright points leave a faint trail and edges look softer than on an LCD. A tiny amount of light also bleeds beyond each lit point, an effect usually described as bloom or halation.
A CRT also has a shadow mask or aperture grille, a fine metal grid inside the tube that makes sure each beam hits only its own color of phosphor. The pattern of that grid, together with the size of the beam, affects how sharp the picture is and how visible the individual lines appear.
Tip: If you want a simulator to look convincing, scanlines alone are not enough. Add a little blur, a soft vignette at the corners and a gentle glow around bright areas.
What is TV static, really?
Static, often called "snow", appears when the set receives no usable signal. The tuner and amplifier boost whatever tiny electrical noise is present, and the screen draws random bright and dark dots. Part of that noise is thermal noise from the electronics, and part comes from natural and man-made radio sources in the environment.
Because the picture is drawn continuously, the static flickers and crawls rather than sitting still. That is why retro TV simulators usually create static with random pixels redrawn many times a second, and why a short burst of noise when you change channel feels so familiar. The simulator on our home page lets you cycle through noise levels to see this effect.
Other CRT quirks fans recognize
- Curvature: many tube screens bulge slightly outward, so straight lines near the edges can look gently bowed.
- Vignette: corners are often a little darker than the center.
- Color bleed: composite connections blend color and brightness signals, which can smear sharp color edges.
- Degauss hum: some sets clunk and hum when turned on as they remove stray magnetism from the screen.
- High-pitched whine: many sets emit a faint tone from the horizontal scanning circuit that some people can hear clearly.
CRT safety and care
Behind the glass, a CRT uses very high voltage to accelerate electrons, and that charge can linger after the set is unplugged. For this reason you should never open the case unless you are trained. Lift heavy sets with two people, keep ventilation slots clear, place the set on a stable stand and clean only the outside with a dry or slightly damp cloth. If a set is beyond repair, recycle it through an e-waste program, because the glass can contain lead. Our vintage CRT buying checklist lists more safety checks.
How simulators imitate a CRT
A good retro TV simulator reproduces the visible effects without any tube. Developers draw a canvas, overlay semi-transparent horizontal lines, apply a radial gradient for the vignette, add a small blur for phosphor softness, and generate random noise for static. Some advanced tools also curve the image and separate color channels slightly. These tricks are cheap to run and work on phones. For the bigger picture of what a simulator is, read what are RetroTVs.
FAQ
What does CRT stand for?
CRT stands for cathode-ray tube, the glass display tube used in traditional televisions and monitors before flat panels became common.
Why do old TVs have scanlines?
The picture is drawn one thin horizontal line at a time by an electron beam, so the gaps and brightness variations between those lines are visible, especially on lower-resolution signals.
What causes the static on an old TV?
Static is amplified random electrical noise displayed when no clear signal is received, so the screen draws random bright and dark dots.
Is a CRT better than an LCD?
Not in every way. CRTs offer natural motion and a distinctive look but are bulky and heavy. LCDs are sharper, lighter and more efficient.
Can I recreate the CRT look on a modern screen?
Yes. Filters, shaders and simulators add scanlines, blur, curvature and glow to approximate the look on a flat panel.
