Private building owners in Hong Kong will be encouraged to use lighting and air-conditioning more efficiently under a code of practice released yesterday.But up to 20 per cent of older buildings would be unable to meet the criteria, said assistant director of the Electrical and Mechanical Services Department Lee Lo-tung. Deputy Secretary for Planning, Environment and Lands Kim Salkeld said reducing electricity use and making energy-efficient alterations to buildings would cut businesses' costs. Mr Salkeld said increased energy efficiency in government buildings had shaved $40 million off power bills during the past five years.