Four fire engines and around 25 firefighters were called to a fire at a house on Midmoor Road in Wimbledon.
Half of the first floor of a semi-detached house was damaged by the fire. One man left the property before the Brigade arrived. He was treated at the scene before being taken to hospital suffering smoke inhalation by London Ambulance Service crews.
The Brigade's fire investigators believe the fire was accidental and caused by the sun's rays reflecting from a mirror and setting light to materials.
A London Fire Brigade spokesperson said: "The sun is especially strong during these summer months but fires caused by refracted and reflected sunlight can happen all year round and are actually quite 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 1541 and the fire was under control by 1653. Fire crews from Wimbledon, New Malden, Wandsworth and Fulham fire stations were at the scene.