Four fire engines and around 25 firefighters tackled a fire at a detached residential property on Coombe Park in Kingston upon Thames.
Part of the lower ground floor was damaged by the fire. There are no reports of any injuries.
The fire is believed to have been accidental and caused by refracted sunlight.
A London Fire Brigade spokesperson said: “Fires caused by refracted sunlight can happen all year round and can be common.
"Our advice is to make sure that you keep mirrors, crystals, glass ornaments and other reflective items out of direct sunlight at all times.”
The Brigade was called at 2022 and mobilised crews from Wandsworth, Kingston, Twickenham and surrounding fire stations to the scene. The fire was extinguished by 2101.