Four industry experts — Grant Grable, vice president, sales and marketing, Sunoptics Prismatic Skylights; Greg Header, president, Solar Innovations Inc.; Ken Laremore, product manager, skylights, Carlisle SynTec; and Stephan Moyon, director of sales, Velux America Inc. — discuss the state of daylighting:

Q. On the commercial/office side, the trend is clearly toward higher ceilings and plenty of vertical glass to give occupants the benefits of daylighting. What are the energy trade-offs, if any?

Grable: In multi-story commercial/office buildings, daylighting through vertical glazing is the only option. To get light deeper into the space, you need to increase the height of the glazing in these spaces. However, as vertical glazing height increases, designers are faced with ways to diffuse directional light and glare. Having the light source come from the window wall will always produce bright contrast when looking toward the source and without diffusion; the glare can be disruptive to office workers as well as interfere with office equipment and monitors. In a single-story building or top floors of commercial/office space, the most cost effective and efficient way to daylight is through the roof, with high-performance skylights that provide the maximum amount of light transmission while still diffusing 100 percent of the light. With high-performance skylights, any space can be properly day lit with only 5 percent of the total roof size. The latest revisions of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 90.1, as well as California's Title 24 energy code, exempt up to 5 percent of the roof value for daylighting due to the huge energy-savings upside during the high-energy demand time of the day.

Header: If a project is not properly engineered, there can be a number of trade-offs for the customer. Trends appear to be leaning toward soft-coat glass technology, which has been improved in recent years. However important glass appears to be, the real value of the project is not just in the glass but also in the structure's underlying system. Skylights for daylighting generally employ glazing with high levels of light transmittance and a high R-value, generally reflective glass, to achieve the best results. Increasing the use of thermal and cellular blinds and dividing the interior space can improve the energy efficiency. Proper planning for sunrooms and conservatories and proper use of passive solar energy can help to alleviate many energy issues that may arise. Exterior shading trees and glass choice can help to minimize heat transfer throughout the year. Four-season rooms should be somewhat shaded and employ a high R-value glazing option in the roof and a heat-gain glazing option in the front wall to absorb solar heat while the angle of the sun is lower during winter months.

Laremore: Because of the ever-increasing price of oil and resultant electrical costs for artificial lighting, an optimally planned daylighting design will always result in energy savings for a building owner when skylights are installed in conjunction with a lighting control system. The savings generated from decreased electrical consumption for lighting will always outweigh the increased costs for cooling and heating. To what degree depends on the geographical location of the structure and the efficacy rating of the lighting type.

Moyon: The trends in commercial building architecture, backed by comprehensive research on the benefits of daylight on human performance, retail sales, higher productivity, and lower absenteeism, strongly favor use of natural light throughout the space through vertical windows or skylighting. Skylights are the only products that can distribute daylight to any area within a large commercial space. Energy Star-qualified products are preferred to minimize or eliminate the energy losses resulting from large expanses of glass. In fact, an Energy Star window or skylight with a high lighting efficacy ratio will generate more light and less heat than a comparable lighting fixture, thereby contributing to savings in lighting costs and cooling. This is very important when lighting and cooling costs in most commercial buildings are estimated to be between 60 percent and 75 percent of total energy costs for a building.