TED Magazine - May 2017

AS OF NOVEMBER 2016, PUT- in-place construction spend- ing in the United States reached $82 billion, a 6.3% increase over 2015. After power and highway and street construction, edu- cational facilities are the largest con- struction market in the country. Today, nearly 55 million students attend school in some 130,000 K- 12 buildings in the United States. Argu- ably, the most important room in these buildings is the classroom, where the majority of instruction occurs.
General Lighting The primary lighting layers in a class- room are general and supplemental lighting. • For general lighting, the Illumi- nating Engineering Society’s (IES’s) RP- 3 standard recommends uniform lighting on horizontal task surfaces, which provides task layout flexibility while promoting alertness and visual acuity. Design light levels depend on factors such as the luminaires’ place- ment, output, and distribution as well as the room dimensions and surface reflectances. Recommended surface finish reflectances are 90% ceiling, 80% window, 70% whiteboard, 5% to 20% chalkboard, 60% wall, 25% to 40% task surface, and light as practi- cal for the floor. The general lighting typically may be segmented into two zones, one for the educator and one for the students. The educator zone focuses on light on vertical surfaces (teaching wall), while the student zone focuses on light on
horizontal surfaces (desktops). The designer must take care to avoid glare (reflections on computer screens and whiteboards and direct glare for the educator), which can be challenging with lower ceiling heights. Daylight is a valuable source of light for classroom general lighting. Ideally, students will be seated with sightlines parallel to windows. Day- light entering the space should be con- trolled with acces- sories such as win- dows or blinds. The Collaborative for High Performance Schools (CHPS) im- poses significant day- light requirements. Luminaires may emit direct or indirect light distribution or a combination of both, such as direct/indirect. With a direct/indirect luminaire, the direct emission places light on the task and produces some shadowing for model- ing. The indirect emission, mean- while, provides soft, diffused ambient lighting that may be more visually comfortable and produce less reflec- tion on computer screens, which may be tilted back. • Supplemental lighting may be added to the educator zone. This light- ing may be part of the general lighting or dedicated lighting such as a white- board luminaire. Its purpose is to raise vertical light levels on the educa- tion surface such as a whiteboard or
IT TAKES THE RIGHT
LIGHT TO LEARN
Lighting and control for K- 12 general-purpose classrooms. by Craig DiLouie
across the entire educator zone. In the latter case, it also draws atten- tion to the educator. Available equipment is con- strained by energy codes, which limit interior lighting with a power allowance expressed in maximum W/sq.ft. ASHRAE/IES 90.1-2010 imposes a maximum allowable light- ing power density of .99W/sq.ft. for school and university buildings if using the Building Area Method and 1.24W/sq.ft. for classrooms if using the Space by Space Method. For commercial building applica- tions where color rendering is im- portant but not critical, a color- rendering index (CRI) rating of 80+ is typically recommended. The CHPS requires a minimum of either 80 or 85 CRI, depending on the selected points package. CHPS options fur- ther require lumi- naires to be RoHS compliant, have an L70 of 50,000 or 100,000 hours if LED, operate with an initial efficacy of at least 50lm/W, and/or produce a percent flicker that is 10% or less across the dimming range. For specific requirements that relate to different points pack- ages, consult the CHPS criteria.
Flexibility The large-scale introduction of pro- jected images in general-purpose classrooms demands flexibility from the lighting system to produce opti- mal viewing conditions. RP- 3 rec- ommends controls that reduce or turn off during audiovisual (AV) presentations, with dimming being desirable for use with video and computer projection systems. The lighting should be capable of at least two scenes: general (normal) and AV (multimedia) instruction. In