Dave Liquorice wrote:
How about a reflection catching the screen at that time. The shape of
the hump looks very similar to ones that the internal plot here gets
when the unit catches the sun.

I was puzzled by the sudden appearance of a brown line in my lawn this
summer (dead straight, very thin and about 1m long). It was only when
I happened to look out of the window late one afternoon that I noticed
the sun was being reflected and focused by a stainless steel garden
fountain I'd put in a couple of months earlier.

It burnt quite a line in the lawn, some distance from the fountain
itself, stopped doing it for a few weeks in late August and then burnt
another one in a different place over a few more weeks in September.

The lawn soon recovers, so I'll live with it but, not having gone
through a whole year yet, I'm a little worried that come the spring it
might start to sear a groove in something just that bit more flammable.
:-)

Regards,

- Tom.