Actually a technology that is in use in many industries from computing to warfare, Electro-optics sees a more basic implementation in audio: compression and limiting. Gain reduction is achieved through the use of special Light Dependent Resistors optically coupled to an electro-luminescent panel. Another method of electro-optical gain control uses LEDs to illuminate the photo-resistor rather than electro-luminescent elements. Both schemes produce a particularly smooth and natural sounding gain reduction which has been used on countless notable recordings. Perhaps the most recognized (and most-copied) electro-optical compressor is the Teletronix LA-2A. Incidentally, electro-luminescent panels are sold commercially as night lights – they’re the ones that look like flat, phospherous green, glow-in-the-dark screens.