Designing the Lit Environment

Overview

This Details article appeared in Architectural Lighting's April 2008 issue and was posted online on 13 May 2008. Kevin Van Den Wymelenberg, then director of the University of Idaho's Integrated Design Lab, opens with a staged argument between a daylighting consultant who wants the electric lights off and an electric lighting designer who wants the architecture lit at night and when the blinds are closed. The question he pursues is how those two specialties, and the rest of the design team, can practice a single "holistic" lighting design, and which techniques and technologies might help.

Key Findings

• Daylight-responsive control systems rarely deliver what was promised. He cites the Heschong Mahone Group's 2005 multi-site study, the broadest field evaluation then available, which found sidelit spaces with photocell controls achieving an average realized-savings ratio of only about 25 percent of the predicted figure.
• Occupant behavior explains much of the shortfall. In an informal walk-through of two Idaho elementary schools, only 18 of 156 south-facing windows had their blinds open, about 10 percent of the available daylight access.
• The market has been slow to adopt daylight sensing partly because the small body of long-term research mostly documents problems: under-realized savings, installation and commissioning trouble, user dissatisfaction, and occupants physically disabling the systems.
• Remedy 1 is the integrated design process, defined by the Pacific Northwest university design-lab network under G.Z. Brown as synthesizing climate, use, loads and systems. Its value here is forcing daylighting designers, electric lighting designers, engineers, interior designers and owners into one conversation about the lit environment.
• Remedy 2 is high dynamic range (HDR) imaging, validated by Mehlika Inanici using consumer cameras and Photosphere software to produce per-pixel luminance maps. In 2006 Lawrence Berkeley National Laboratory used HDR-calibrated perimeter sensors at the New York Times headquarters to drive automated blinds against glare, and Sarkar and Mistrick (Leukos, 2006) tested HDR for electric-light control.
• Remedy 3 is tunable color temperature. Occupants often notice the color shift when electric light dims out and daylight takes over even when the light level barely changes; a fixture mixing warm and cool dimmable lamps, such as Philips' Dynamic Lighting, could blend with daylight rather than fight it.

Why It Matters for Daylighting

The 25 percent figure is the number to remember, and the reason it matters for toplighting is that it comes from sidelit spaces. Windows depend on blinds, and blinds depend on people. Diffusing prismatic skylights over a warehouse or manufacturing floor have no blinds to close and produce far more uniform illuminance, which is one reason the same Heschong Mahone research found skylit spaces with controls performing much closer to design intent. The article's remaining lessons transfer directly: photosensor systems fail when nobody commissions them or explains them to the tenant, and the integrated-design habit of putting the electrical contractor, roofer and controls vendor in one room early is the cheapest insurance an owner can buy. The color-temperature observation is also worth noting for high-bay retrofits where LED fixtures at 4000K or 5000K now sit beside 6500K-plus daylight.

About the Source

Architectural Lighting was the principal U.S. trade magazine for lighting design; its archive now lives on Architect magazine's site. Kevin Van Den Wymelenberg later moved to the University of Oregon, where he leads the Institute for Health in the Built Environment, and co-authored Daylighting and Integrated Lighting Design (Routledge). The library copy is a four-page browser printout from August 2014 of an article that runs roughly eight minutes online, with a five-image slideshow not reproduced in the PDF. The full text is on the publisher's site.