[spokeshave]

Could be true....I was at a building construction site last week....they had just installed double glazed windows on 48 apartments....at one place in the courtyard I felt hot...on walking back and forwards I discovered an area about 1 square foot that was caused by the concentrated reflection from the sun....

....seems to me the double glazed windows have a partial vacuum inside....this causes a slight curvature of the glass....(concave for those in Rio Vista) and resulting long focal length with concentration of solar energy. ...

The law of unintended consequences....

[spokeshave]

1).....so purchase a BIG square double glazed window....and a vacuum pump....

2)...couple the vacuum pump inlet to a small pipe glued into the side of the window frame

3)..Place the window to reflect the sunlight back at the neighbor

4) pull a vacuum and adjust the curvature of the glass for focus on the neighbors house....

5)....watch it burn down...

6)...remove your window and pump and retire inside.