Low-emissivity (low-E) window glass — a green technology prized for keeping homes warm in winter and cool in summer — can in rare cases concentrate reflected sunlight strongly enough to set fire to neighbouring property. The glass carries a thin metal or metal-oxide coating that admits visible light but reflects infrared heat; when a pane is slightly bowed, it behaves like a magnifying glass, focusing that reflected heat on a single spot or line and creating a fire risk that matters for homeowners and installers alike.

Reported effects include scorched wooden decking, melted artificial turf and damaged plants, while one extreme case saw a series of fires traced to a neighbour's newly fitted low-E windows — after three fires in a week, the affected homeowner moved a propane tank away from the focal point. Architects already know to avoid the curved reflective glass responsible for so-called "skyscraper death rays" on large buildings, but the domestic version is less obvious, as any poorly manufactured low-E window could potentially become a firestarter.