Michael Lane LC

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School Classrooms
February 1996

Just as with office building, school classrooms are seeing a dramatic shift in the lighting requirements. Today's classroom must have a lighting system that can provide high levels of light for the reading tasks while providing glare-free lighting on the computers. In addition, the lighting system must use the least possible amount of energy. It was much easier to design the lighting system when the computers were primarily in computer classrooms, not all classrooms. These changes place heavy demands on existing classroom lighting systems and schools' tight budgets.

The IESNA has two publications that should be referenced when designing, redesigning, or retrofitting a classroom lighting system: ANSI/IESNA RP-3-1988 Guide for Educational Facilities Lighting, and ANSI/IESNA RP-1-1993 Office Lighting. RP-1 is for office lighting, but the recommendations, particulary those for computer VDTs, can easily translate into classrooms.

In any lighting retrofit or redesign, the first consideration is whether or not the existing footcandles are adequate for the tasks. Use IESNA recommendations for classroom lighting, unless there is a state-mandated minimum footcandle requirement that is higher than the IESNA recommendation. If you look in the IESNA Lighting Handbook under Educational Facilities Classrooms, you will be referenced to Reading for many of the tasks. Under Reading there are 34 different tasks listed, with 14 of the tasks falling into category D (20-30-50 footcandles -- performance of visual tasks of high contrast or large size) and 14 of the tasks in category E (50-75-100 footcandles -- performance of visual tasks of medium contrast or small size). With school classrooms, the light level should be between 20 and 100 footcandles, quite a spread.

I will go out on a limb and say 50 footcandles maximum for the classroom, not much of a limb when you consider it is the high end of category D and the low end of category E. Remember that when computers are present in the classroom, this light level will be 5 times the IESNA recommended levels for VDT screens. Based on this recommended level, go out with a good digital footcandle meter and measure the light levels in the classrooms to see how they compare. Is it overlighted? Is it underlighted? The answer will dramatically affect the design options.

Designing the lighting system for a new school classroom is easy compared to redesigning or retrofitting classroom lighting. With new classrooms, lighting designers can work with the architect to design a lighting system that works with the architecture, is energy efficient, provides a high quality lighting environment for the tasks, and is within budget. However, existing classrooms provide a significant challenge since often the reason the lighting system is being redesigned is to save energy, not to improve the quality of the space.

So, can we save energy and still provide good quality lighting in these existing classrooms? Hopefully, you answered yes, because quality lighting for the end-user is what good design is all about.

The energy part of the equation is simple. Use T8 lamps and electronic ballasts in either the existing luminaires or in new luminaires. Remember that retrofitting the T8 into an existing luminaire will provide similar light levels to the F40T12/CW and 14% higher levels than the F40T12/CW/ES lamp. Caution should be taken in doing a straight one-to-one retrofit because the end user will see an increase in the light levels either way due to the lumen depreciation of the existing lamps and the luminaire dirt depreciation factors.

The hard part is improving the quality of the space. Sure T8 lamps have better color properties that the T12/CW, and the electronic ballast will eliminate fluorescent lamp flicker. Parabolic fluorescent luminaires that follow RP-1 will eliminate computer screen glare, but may not meet the clients budget. With parabolic luminaires, don't forget about lighting the walls, especially the teaching wall, to eliminate the cave effect produced by parabolic luminaires. Direct-indirect or completely indirect luminaires may be the best solution for producing a comfortable, low-glare lighting solution. Unfortunately, pendant luminaires are more expensive than parabolic luminaires and require a higher ceiling (9 foot minimum ceiling height) to effectively light the space.

Another answer to the quality question may not be in the changing the luminaire, but in changing the room. A new paint scheme using highly reflective light colors like white (not blue, red, or green) is an easy option that will increase the footcandle levels. Suggest to the end-user that they rearrange the room so the computer screens do not face the windows or a large expanse of luminaires. Place the computers along a wall or in the corner so the screens face the wall, and switch the lights over the computers separately from the general area lighting. These last options may have the biggest effect on the quality of the space than changing out the lighting system, and may be the most cost effective.