Illuminating students

Lighting is such a subjective thing.

05/01/2008


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.

Taking control

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.

The light of day

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.

Tips from the desert

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.



Tricks of the trade

Tom Foster, PE, president of

1. Solar light levels should be based on a median level of lumen output for the device used based on the project location. An analysis can be run for seasonal minimums and maximums to find the range of solar contribution.

2. The controls should have an adjustable response delay so the short-term transients in solar light levels (due to fast-moving clouds or aircraft shadows) do not unnecessarily switch the lights on/off. This is less of an issue if a dimming system is used, but very important for switched systems. Nescience switching is very disruptive in the classroom.

3. If the facility uses rooftop air conditioning units, or other significant rooftop equipment, perform a shadow study to optimize solar device roof locations.

4. Have strict drawing and specification requirements for solar device locations such that any relocation due to structural, piping, or ductwork is first coordinated with the lighting designer.

5. Classrooms usually require the ability to darken the rooms for presentations. This requires a method to close the solar devices. Use a product with a proven track record of interfacing with the control system.

On the lighting horizon

Everyone always wants to know about the Next Big Thing. Whether it's for personal gain (like the best stock options) or for professional development, we're always clamoring to know what the latest and greatest technology will be. Here are two:

LED lights

LEDs are beginning to be considered for some niche general lighting applications. Low light-level requirements are most primed for consideration including step lighting, night lighting, accent downlighting, architectural/entertainment lighting where color is the driver, and emerging outdoor site lighting applications.

The biggest barrier in these emerging markets is high initial cost until the volume or industry players make it more competitive to current available and proven source technologies.

Based on some of the new products scheduled to be on display at Lightfair International, Las Vegas. LEDs are on the market with designers in mind. They're classy and trendy at the same time, and their performance levels are becoming attractive.

Specific locales have different codes for LEDs, however, so they're not completely standard across the board. They're also unfamiliar to electrical inspectors, so even if you've specified everything right, the inspector may not fully understand the system.

According to Robb Allen, AIA, IES, president and director of technical services at Clear Stream Studio, Green Bay, Wis., the future of solid-state lighting holds exciting potential if/when major technological and economic challenges are met head-on.

• Efficacy improvements in lumens per watt are improving dramatically for bright white LEDs to compete with other sources, but lag far behind in warmer color temperatures important in many architectural applications.

• While the visible light from the LED is cooler than many other sources, a massive amount of heat is produced on the “backside,” or chip side, of the LED. This heat currently requires roughly a 2-in. cube of aluminum heat sink to dissipate the heat generated from just a single, 1 W LED. You can imagine the size, scale, and cost related to producing a general illumination luminaire that would require dozens to hundreds of these LEDs to produce the lumens required to meet most commercial applications.

• Lamp life originally touted at 100,000 hours, now in general is promoted at 50,000 hours and is driven totally by the actual thermal conditions at a critical location within the chip, which is totally dependant on the design of the luminaire and the ambient environment temperature range where it's installed.

Digital lighting controls

There's a movement toward going digital and/or wireless with controls, mostly because of the savings. It eliminates conduit/pipe, which can save 35% of the overall electrical construction costs because copper, steel, and a lot of labor are reduced. Everything is low-voltage and is controlled by DALI, or

Due to the fact that the entire lighting system is highly customizable, the potential is ripe for miscommunication or unrealistic expectations at an affordable price. Commissioning is the only way to ensure that a system like this works properly. And initial set-up can be time-intensive due to software programming issues that are only beginning to be simplified without calling in the “Tech Squad.” Once it works, however, it works well, and maintenance is often simple programming changes.



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