A new survey shows parents turn off the light in an empty room 333 times a year.
It's estimated leaving lights on unnecessarily can cost families an extra â‚¬12.50 a year.
The poll by Uswitch.com, found having to switch off the TV when no one is watching is next biggest bugbear for parents.
Parents claim they turn off the TV an average of 218 times a year, which causes 45 arguments.
The price comparison website says households without children claim to argue less, but couples still admit to having disagreements about energy.
The survey claims partners fight on average 37 times a year about the cost of heating thier home.