Three advanced daylighting technologies for offices

Coated low-emissivity glazings have achieved widespread market penetration and user acceptance as a means of utilizing daylighting while obtaining net energy savings. Several less conventional technologies, including light pipes, prismatic panels, and electrochromic glazings are still undergoing development in order to overcome barriers of architectural integration, cost, and user acceptance. Barriers for each of these three technologies are considered in the context of a hypothetical daylighted private office workplace (with display screen tasks) and adjacent corridor. The lighting control strategy for each case includes both automatic and manual controls, including window, room, and task lighting controls from the display-screen operator-position. Assumptions concerning manual switching of room lighting are based on a recent study of daylighting potentials in office workplaces of similar size and furnishings. Office and corridor ceiling heights, configurations, and finish surfaces appear to be critical to both architectural integration of and light distribution from light-pipe and prismatic-panel systems. Integration of electrochromic glazings now appears to be limited by wiring needs and glazing appearance in its reflective (colored) state. The costs for each of these technologies remain high and cannot at this time be justified by energy savings alone. It appears, however, that electrochromic glazings, expected to be commercially available within three years, hold the greatest potential for both personal control of lighting and thermal conditions, in addition to energy savings. Occupant response to these technologies, however, has not been adequately assessed.