Illuminating students

Lighting is such a subjective thing. Some designers aim for the maximum prescribed foot-candles in all situations, figuring the client will want everything to be as bright as possible as code allows. Others create intricate designs that meet the average standard foot-candle recommendations for the space, leaving shadows and hot-spots that are awkward and inefficient to some, yet dramatic and interesting to others.

Still other lighting designers try to see how low they can go, and aim for the least amount of kilowatt hours consumed to help reduce energy costs and carbon emissions. This may be the best option in schools, which tend to require varied lighting design solutions for its different types of rooms—and also have some of the tightest budgets.

According to ASHRAE 90.1-2004 and the Illuminating Engineering Society of North America (IESNA), the lighting level should be determined by the visual task. If the task is more intensive, such as intricate drafting or detailed work, the light level should be higher. Most K-12 classrooms, however, don't have highly intensive visual requirements anymore due to the influx of technology and computers, meaning that lighting levels can be designed fairly standard in each classroom, which is what we'll discuss here.

Lighting can suck up a large amount of any school's energy costs, and both school officials and lighting designers are looking for quick fixes to reduce this cost. Upgrading fixtures and ballasts can increase efficiency as much as 40%. But tightening budgets and rising energy prices demand that lighting designers and engineers do more. What's left? Take control of the lighting systems.

A school building is a 20- to 50-year investment, so by selecting the right products and control system, O&M costs can be controlled over the life of the building.

Lighting controls can function many ways within a school:

• Occupancy sensors, so lights turn on only in a classroom with students or activity
• Timed lights that turn on and off during certain parts of the day and change as daylight changes through the year, or as scheduling events dictate
• Photosensors that react to changing daylight levels within a classroom that dim or turn off electric lights when not needed
• User-controlled dimmable systems that are adjusted according to the visual needs of the teacher.

James R. Benya, PE, FIES, principal at Benya Lighting Design in West Linn, Ore., says that ASHRAE 90.1-2007 will most likely include a credit for adding lighting controls. Therefore, control systems that reduce wattage per square foot will be given the credit they deserve. This reduction increases energy efficiency, which reduces energy costs and will help owners and engineers obtain points when applying for USGBC LEED points, for example.

Benya suggests going one step further. He said that to beat the code, know what technology was used when the code was determined, and use a better technology. By staying ahead of the technology curve, lighting designers will not only design schools with better lighting options, they'll save money along the way, especially if they keep up with appropriate O&M.

The trick is to dictate what kind of lighting is needed in a classroom before selecting a control system. For example, many high schools teach several classes on computers (or students' laptops), which requires a different type of overhead light—without glare. Also, because blackboards are a thing of the past, lighting on white erase boards is a whole different ballgame.

Dimmable systems set up in appropriate zones offer the right lighting in multimedia classrooms or those with audio-visual options. It's key in these cases that the teacher can override the programmed lighting system so that lighting is darkened for screens at the front of the room, but students in the back of the room can still take notes.

Lighting designers can't discredit the benefit of good daylighting. According to “Daylighting in Schools,” a study of 21,000 students done in 1999 by the Heschong Mahone Group, students' test scores improved up to 26% with appropriate daylighting. But what's appropriate?

If every school could face north and receive even, diffused light throughout the school year, this whole daylighting discussion would be pointless. But not every building can be sited that way, and schools typically are in session during the darkest, dreariest days of the year.

Appropriate options abound, but many lighting designers forget that less can often be more. While side (window) lighting is beneficial, it's often not the best type of daylight, especially if photosensors aren't incorporated into the lighting design. One half of the classroom may be over-lighted if overhead lights don't turn off when sunlight pours in a window.

And the intensity of direct sunlight can create hot spots and wreak havoc with the HVAC system. This is especially common for older large clear or diffuse glazed large ceiling skylights, which often create intense daylight in a small area on the classroom floor and emit large amounts of radiant (heat) energy into the space. In most cases, air conditioning is forced to compensate for poor daylighting control, offsetting any energy savings that might have been gained by including daylighting in a design, or worse yet, increasing energy use.

Smaller skylights as well as skylights that track and/or diffuse the sun's rays, especially those that control light distribution throughout a room and whose lighting levels can be controlled by the teacher, may be the best bet. Most daylighting industry design references recommend and national energy codes limit skylight area (square foot) to floor area (square foot) ratios to 3% to 5%. Most computer modeling illustrates this to be the best balance in providing appropriate energy saving daylight without creating a net negative effect by overtaxing heating and air conditioning systems using current available technology.

Some areas of the country offer utility-driven incentive rebates for reducing electrical energy consumption, so incorporating skylights into a design can save the school even further. School buildings are open during peak energy usage hours, so if you design for less energy use, you're saving the school district even more money, speeding up the payback on relatively costly upfront investments like skylights. Remembering that schools are long-term, 20- to 50-year investments, design professionals and school board members need to reinforce with the public during referendum time that true costs are the long-term lifecycle costs, not just the initial cost everyone often focuses on.

In 2007, Fay Herron Elementary School in North Las Vegas, Nev., completed a retrofit of its classrooms to improve both lighting and daylighting. When tasked with this project, the school district decided to approve two options: light sensors and tubular skylights. Classrooms had no natural sunlight, so engineers and lighting designers realized that by adding a lighting control product and allowing natural light into the classrooms, they'd save money and improve the quality of light.

Each room was equipped with passive infrared sensors that measured the light level. If the room was occupied, lights would turn on and the skylights would open, based on the amount of light needed. Previously, each room was artificially lighted to 100 foot-candles; today each room is artificially lighted to 55 to 60 foot-candles, cutting lighting requirements (and cost) in half. The tubular skylights were tuned to measure the outside light levels, and subsequently controlled the amount of sunlight they allowed in.

Each classroom holds a control cabinet with a relay, control pad, and occupancy sensor. The controls can be overridden by the teacher, key to teaching with multimedia presentations or when extra light is needed for difficult tasks.

In the case of Fay Herron Elementary, each room's control system stands alone. Some schools, on the other hand, may decide that all classrooms should be on one main control system, or timers should turn lights on/off at specified times based on the time of year.

The combination of both lighting controls and daylight offered a win-win situation for school officials and students.