Energy saving light glows every 30 seconds when turned off?

I’ve a standard energy saving light bulb in a room where I keep my PC, there are no windows in the room, but I’ve noticed the light bulb glows every 30 seconds when turned off? At first I thought it was a reflection from a LED on one of the items of computer gear, so I turned everything off, still happens? No... show more I’ve a standard energy saving light bulb in a room where I keep my PC, there are no windows in the room, but I’ve noticed the light bulb glows every 30 seconds when turned off? At first I thought it was a reflection from a LED on one of the items of computer gear, so I turned everything off, still happens? No mobile phones or wi-fi / Bluetooth devices / known transmitters in house, so what is making this bulb glow?
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