There are three potential reasons that come to mind, one is a conspiracy, the other a medical ailment and the latter is just the increase in modern technology causing encroaching.
Firstly a retinal disattachment can cause "light effects" It's to do with how the connection in the eye socket is mounted and what happens if the mounting is displaced a little. In fact there are many reasons for displacement like blood pressure, lack of vitamin C in the diet that causes crystalisation even Stigmatisms (mishaping of the eye). However if it's an eye problem, it's likely to occur more than once.
The conspiracy... A television is a funny thing, especially in countries where you might need a licence to be watching one. It's possible that signals can be sent to the antenna to appear on screen and might have even been done on occasion with certain television companies misusing their technology to get back at freeloaders that aren't paying licence fees. (They might of just as well started sending men round with Italian Suits and baseball bats and demand payment).
It's even suggested that the above accounts for a number of "Psychosis phenomona" involving television interaction thats is "Suggested" personal interact with the viewer like the viewer is a private audience, this can be seen as a form of dimensia and the individual is then refered to as a patient.
Lastly with the current increase in things like WIFI, wireless keyboards, mice, networks, and of course telephones the likelihood is that any forms of interference could have caused it.
Don't of course read too much into the conspiracy or go hypocondriac on me, afterall I'm just giving you potential answers and suggest to not worry too much about it. Afterall if you go looking for a conspiracy, your more than likely to create one.