While most Yalies sleep, some of the University’s buildings stay up burning the midnight bulb.

In the University’s Sustainability Strategic Plan 2010-2013, released this month, Yale administrators announced their intent to evaluate and improve the energy efficiency of the campus’s buildings. Michael Stringer, a central campus facilities supervisor, said that reviewing sources of energy consumption in buildings is one of the Office of Facilities’ top priorities. But at 12:30 a.m. Sunday morning, numerous rooms from the School of Art to Kline Biology Tower up Science Hill illuminated the empty sidewalks. Both the School of Architecture and Green Hall on Chapel Street were so well-lit, in fact, that a passerby could see individual items on cubicle desks several floors up.

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The challenges facing the reduction of night lighting are more complicated than one might think, Director of Facilities Operations Louis Annino said in an e-mail Tuesday. State laws, building infrastructure and rogue students all contribute to the prevalence of building lighting at night, and all require different approaches to ensure increased energy efficiency in campus buildings.

Andrew McCreary ’12, a coordinator for the Student Taskforce for Environmental Sustainability, said the group has been working with the Office of Facilities to try to reduce unnecessary lighting within residential spaces.

“In some cases the lights were left on to give light to students who are unable to turn on and off lights for religious reasons,” McCreary said.

On Sunday night, rooms in Harkness Hall, laboratories on Hillhouse Avenue, the School of Management and year-old Rosenkranz Hall were all brightly illuminated, but vacant.

Sometimes it is students themselves who make increasing energy efficiency in campus buildings difficult.

Joe Kruote ’13 said he knows students who stay in William Harkness Hall, one of Monday’s lit buildings, outside of normal operating hours to use the rooms for study purposes.

Three of the six students interviewed on Cross Campus after midnight on Monday said they have noticed classroom and lecture hall lights on past normal teaching hours.

Yale buildings must comply with Connecticut building codes which contain a standard of illumination, Annino said, noting that these codes require minimum lighting in entryways and corridors for cases of emergency.

The state code requires that exit pathways be illuminated while a building is occupied, and structures like the School of Architecture, while not necessarily used all night long, are usually considered occupied because of the 24-hour access afforded to graduate students and professors. Stringer said facilities staff are prevented from eliminating night lighting by these regulations, but added that he was not certain whether the University has its own additional codes.

The infrastructures of older buildings are also a barrier to sustainability, Annino said, because many of them cannot support energy-efficient technology, like motion-sensor lights.

But the new Sustainability Strategic Plan is particularly devoted to tackling the energy inefficiency of building lighting.

Both Annino and Stringer highlighted the plan’s commitment to replacing, where possible, permanent lights and manual lights with motion sensor-triggered illumination. On Wednesday afternoon, all central campus facilities supervisors met to discuss the practicalities of installing such a system, Stringer said.

“It’s not much of a cost to change a light switch and it saves a lot of money in the end,” he said. “It is a major University initiative.”

But Stringer said Facilities Supervisor for Cross Campus Marilena Stephens reported during Wednesday’s meeting that only half the classrooms in William Harkness Hall have been converted to motion sensor illumination systems so far.

Stringer said he expects the majority of the campus’s retrofitting to happen fairly quickly.

“WLH is not nearly as much of a dinosaur since it did get partially retrofitted a few years ago,” he said.

The University plans to reduce campus energy consumption by 15 percent below the 2005 level, according to the 2010-2013 Sustainability Strategic Plan.