SACRAMENTO — Home day care operators in California must stop smoking in their houses, even after hours when children are gone.

Gov. Jerry Brown announced Friday he had signed AB1819, joining 12 other states with similar bans that target "third-hand" smoke.

Smoking during day care hours is already banned. Democratic Assemblyman Isadore Hall of Compton says his bill responds to the dangers of smoke that lingers in furniture and carpets.

A recent study by Lawrence Berkeley National Laboratory found such smoke damages DNA in human cells and is especially dangerous for children.

Operators at 36,000 home facilities face penalties of $100 and revoked licenses for lighting up. Smoking in backyards and outside the home is still permitted.

The bill takes effect in January.