What is an Aperture Grille? An Aperture Grille refers to a method of CRT construction employing vertical strips of colored phosphor with a thin screan formed of a grid of tiny metal wires. Electron beams emitted from the electron gun pass through this grid of metal wires and lands on the appropriately-colored phosphor strip, exciting phosphors that produce the on-screen image. An aperture grille construction tends to produce brighter, more saturated colors, but is not as good for text or fine detail.