Four fire engines and around 25 firefighters were called to a fire at a house on Oakley Road in South Norwood.
Most of the first floor of a terraced house was damaged by fire and part of the roof was also damaged by the blaze. A woman and two children left the building before the Brigade arrived. They were all treated on scene by London Ambulance Service crews and were taken to hospital.
The Brigade's Fire Investigators believe the fire was caused by sunlight coming through a window, which was refracted by a reflective surface and ignited nearby materials.
Station Commander Graeme Hunter, who was at the scene said: "The sun is especially strong at the moment but fires caused by refracted 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.”
"It's also really important to make sure that you have a working smoke alarm on every level of your home."
"The residents had a very lucky escape, as there were no working smoke alarms in the property.
"We urge people to have working smoke alarms on every level of your home and to test them regularly. Smoke alarms will give the earliest possible warning if a fire breaks out in your home.
"Ideal spots for smoke alarms include rooms where you leave electrical equipment running like satellite boxes, computers or heaters; any room where you smoke, and anywhere you charge your mobile or laptop.
“As a minimum you should have smoke alarms on every floor - in the hallways and the rooms you use the most, plus a heat alarm in the kitchen and the bathroom. They should be tested regularly."
The Brigade was called at 1321 and the fire was under control by 1518. Fire crews from Woodside, Beckenham and West Norwood fire stations were at the scene.