LG's transparent TV tech starts with OLED (not to be confused with QLED). It stands for organic light-emitting diodes; they are self-lighting pixels, which means they don't need a separate backlight like LCDs. LG's transparent OLED panel uses a modified pixel structure where the light-emitting portions are shrunk and spaced out, leaving gaps between them that allow light to pass through. The trick is using materials like indium tin oxide for the wiring; it's conductive but mostly see-through.
The real challenge is the transistors. These are normally opaque, but LG uses IGZO (indium gallium zinc oxide) instead of traditional silicon to shrink them down and reduce visual obstruction. Everything is built on a glass substrate that also has to remain optically clean. To protect the sensitive OLED materials from moisture or air exposure (which would kill them), the panel is sealed in a transparent encapsulation layer.
So while it looks like a floating hologram, the screen is basically a tightly packed grid of translucent components with just enough space for background visibility. It's not glass-clear (you'll still see some darkening), but it's transparent enough to create that futuristic floating image effect. LG claims around 45% transparency.