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Sprites are a gas discharge phenomenon in the mesosphere powered by the charge moment change from large lightning strikes within major convective thunderstorms. Typically, only 0.1% of all lightning strikes produce a sprite. Bright optical emissions of nitrogen appear around 40-90 km altitude for 10s of milliseconds. These may be observed by naked eye but are rarely reported. The phenomenon was predicted in 1925, first recorded in 1989 and first observed in South Africa in 2016. Here, the sprite occurrence rate is such that in less than one week more sprites are observed than in a whole decade in Europe. We use ground-based night-vision TV cameras fitted with optical filters to estimate the electron energy (which is of order 5 eV), and from this the electric field (which is of order 100 V/m), within a sprite.