Climate Change Adaptation Strategy

From working and travelling around London I have beomce increasinlgy aware that there is a significant amount of office space standing empty that continues to be fully lit (even in full daylight most of the time) in order to help sell or rent the space.  Why don't we just turn the lights off and stop wasting energy lighting empty space for hours and hours a day? It feels as though there could be a relatively straightforward directive given to property managment firms giving 'hours of lighting' or similar guidleines around how and when empty commercial space can be lit.  Or it could take the form of a charter that firms can sign up to which might prove more appealing in our envirnmentally conscious times.It feels as though this would be relatively easy to measure the potential savings that could be made both in terms of energy and money.