What lightning does to your television

By Marcus Wilson 29/01/2010

   Well, last night’s thunderstorm was a bit of a feeble affair after the fireworks of Wednesday. There were a few flashes, the odd rumble, and a bit of rain, but it cleared away after an hour. Maybe somewhere else got the drenching this time. Still, it makes four days in a row of the same daily weather, almost hour-by-hour. And this morning….is shaping up the same way…

A student of mine sent me these photos of his television screen on Wednesday night (used with permission).  There was a lightning strike close to his house, which seems to have magnetized the television.  The picture is there, but the colour is wrong.

lightning.jpgIn an old CRT television, each point on the screen contains a phosphor – and there are three different colours, red, green and blue. To make up the colour picture, the phosphors are stimulated by the required amount, by a beam of electrons that hit the screen from behind. The beams are scanned across the screen using magnetic fields (charged particles like electrons are bent by electromagnetic fields), and, in order to hit the right phosphor, need to emerge in the exactly the right direction.  What I think has happened in this case is that the lightning has permanently magnetized some part of the television. This is hardly surprising given that lightning carries a huge direct current, and consequently creates a nice magnetic field around it.

So as the electrons pass, they are bent slightly but consistently off course, and hit the wrong colour phosphor. Hence the image looks right, but just with the wrong colours. De-gaussing  the TV removed the colour shift, putting it back how it should be.

what should look like.jpg