LED displays
Anatomy of an LED screen: from chip to cabinet
An LED screen looks like a single whole, but it is a build-up of layers: from the microscopic chip that makes light to the watertight cabinet that protects everything. Here you see every level.
A large LED screen is actually made of a great many tiny lamps: the LEDs. Those lamps sit neatly in rows on little boards (circuit boards), and all those boards sit together in a sturdy, watertight cabinet.
Each lamp has three parts: a minuscule chip that makes the light, a shiny cup beneath it that bounces the light forward, and a lens that magnifies the light and aims it in the right direction.
An outdoor LED screen consists of separate LEDs or clusters of LEDs, soldered onto circuit boards housed in a weatherproof cabinet. From small to large: chip → LED lamp → pixel → module/panel → cabinet.
The LED lamp from the inside
An LED lamp contains an LED chip (or ‘die’) that produces the light. The chemical composition of the semiconductor layers (epitaxy and substrate) determines the wavelength, and therefore the colour. Beneath the chip a reflector cup bounces the light forward; that cup also serves as the negative terminal (cathode), while a wire forms the positive terminal (anode). A lens magnifies the light and sets the viewing angle (typically 30° or 70°).
Pixel, module and cabinet
One pixel consists of a cluster of LEDs (on full-colour screens, a red, a green and a blue one). Pixels sit on modules; modules together form the screen. Besides the LED panels, the cabinet also holds the power supply and the communication electronics. For outdoor use, that cabinet is sealed to an IP protection rating.
The build-up is hierarchical: semiconductor chip (die) → package (LED lamp) → pixel → module/tile → cabinet. As current passes through it, the die converts electrical energy into narrow-band light; epitaxy and substrate (e.g. AlInGaP for red, InGaN for green/blue) determine the wavelength. A reflector cup and lens/encapsulant collect, protect and aim the light; the lens sets the viewing angle.
Packaging technology
How the chips are packaged determines the achievable pixel pitch. With discrete (DIP) LEDs, each colour has its own housing with through-hole leads; with SMD, R, G and B sit together in a single surface-mounted package; with COB, the bare chips lie directly on the board beneath a resin layer. See the article discrete vs SMD.
System components
Behind the LED panels sits a chain of power supply (or supplies), receiving cards and a controller/processor that distributes the image signal. The cabinet provides thermal dissipation and, for outdoor use, an IP rating against dust and water (front and rear may have different classes). Brightness, refresh rate and colour depth are driven by that electronics.