A beaming crystal knob sent a bedroom up in flames after the sun refracted through it.

The shiny doorknob started a house fire in Rodenhurst Road, Clapham, on Monday, July 7, at 8.20am.

The culprit: A shiny crystal knob (Picture by LFB)

The sun’s rays refracted light through the door knob and onto a dressing gown, hanging from a door, setting it on fire.

The house was empty at the time and a smoke alarm alerted builders working on an adjacent house who called the London Fire Brigade (LFB).

Charlie Pugsley, from the Brigade’s fire investigation unit, said: “Crystal and glass ornaments and items such as shaving mirrors should be kept out of direct sunlight.

“The homeowners are lucky they had a working smoke alarm which alerted some local builders who quickly called the Brigade.

"Part of the bedroom was damaged in the fire but it could have been much worse.”

LFB have warned people to keep shiny objects away from sunny sills, fit a smoke alarm on each floor and if you have a fire to close the door and call the fire brigade.

Firefighters from Clapham and West Norwood attended the scene and the blaze was under control by 8.40am.