Twenty firefighters tackled a blaze at two houses in Colliers Wood believed to have been caused by sunlight.
It is thought the fire in Briscoe Road started after combustible items left near the curved glass were ignited by the sun's rays.
The crews had the fire, which spread across two terraced properties, under control by 8.40pm. No-one was injured.
London Fire Brigade is advising homeowners to keep glass jars and mirrors away from the sun.