Corona discharges are luminous signs of strong local electric fields allowing a continuous discharge into the surrounding atmosphere. They commonly occur at the ends of conductors at high voltage. Here we report the observation of a faint glow surrounding an insulating cm-sized box filled with mm-sized basalt beads. At an ambient pressure in the mbar range two light bands occur as soon as and only if the box is vibrated and only if it is filled with a granular medium. In addition, a glow also occurs at the inside of the box. We measured periodic electric fields at the outside of the box with spatial peaks at the positions of the light bands. The period correlates to the vibration frequency. These observations imply strong alternating fields beyond atmospheric breakdown, which are generated inside and also emerge at the outside of the insulating box. The observations can be explained by tribocharging and periodic displacement of charges between grains and the inside walls of the box.

电晕放电是强局部电场的发光迹象，允许连续放电到周围大气中。它们通常出现在高压导体的末端。在这里，我们报告了在一个装有毫米大小的玄武岩珠的绝缘厘米大小的盒子周围观察到微弱的光芒。在 mbar 范围内的环境压力下，只有当盒子振动并且只有当它充满粒状介质时，才会出现两个光带。此外，盒子内部也会出现辉光。我们测量了盒子外部的周期性电场，在光带位置有空间峰值。该周期与振动频率相关。这些观察结果暗示了大气击穿之外的强交变场，它们在内部产生，也出现在绝缘箱的外部。观察结果可以通过摩擦充电和颗粒与盒子内壁之间电荷的周期性位移来解释。