Crystals reflected sunlight through a window and caused curtains to catch fire at a home in Twickenham on Sunday.
Firefighters were called to the four-bedroom property in Waldegrave Park at 2pm to reports of flames spreading to the ceiling.
The blaze was said to be caused by crystals which were hanging in the window and had reflected sunlight on to the curtain, causing them to catch alight.
Crew manager Ian Devine, from Twickenham fire station, said: "Fortunately, the occupants had a fire alarm but the young daughter was about to leave the property.
"We got there quite fast and the fire was localised to the curtains.
"Another five minutes and the bedroom above would have gone up."
Mr Devine added displaying items such as crystals and mirrors close to windows can be dangerous, especially those facing south.
He said: "We have had a fire where someone left a mirror on a side cabinet in their bedroom which caught sun rays and set a door frame on fire.
"There have been three or four incidents with mirrors over the past three or four years."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here