Environmentally Responsible Daylighting Design

 Daylight, part of the nonenergized system, is an important component of environmentally responsible lighting design. Architectural daylighting design decisions can help or hinder the potential for effective use of daylight and achieving visual comfort inside buildings. While a detailed development of daylighting design is beyond the scope of a discussion of environmentally responsible interior design (ERID), the integration of daylighting with electric lighting is important. “ Daylighting, ” a section from the Whole Building Design Guide , provides a substantial discussion of all aspects of daylighting (Daylighting n.d.). An understanding of the issues, benefits, and guidelines related to daylighting is important to developing ERID.

Windows provide a psychologically important connection to the outdoors. Access to a view and interaction with daylight provide valuable environmental information: a dynamic measure of time passage, information about immediate weather conditions, and a sense of place. Having a view to the outside reduces eye strain, allowing the muscles contracted from extended near - focus to relax. Research evidence from education, corporate, retail, and health-care settings is confi rming the positive health and performance impacts of daylighting.

A major benefit of daylighting is the reduction in both fossil fuel and electric energy use. Fossil fuel is used for heating and cooling, while electric energy is used for lighting. Daylighting can provide savings of 35 to 65 percent in electric use for lighting and 20 to 60 percent overall energy savings. Coupled with energy - efficient and effective electric lighting, the savings will be even greater. Energy budgets can be substantially reduced to well below American Society of Heating, Refrigerating and Air - Conditioning Engineers, Inc. (ASHRAE) Standard 90.1 requirements.

Daylighting does have limitation and liabilities that must be addressed for its successful use in interior environments. Using daylight requires recognition of the variability of this light source due to geographic location, time of day, time of year, and weather conditions that affect the sky; this affects the color of the light as well as the brightness and distribution.

The problem is not so much daylight but, rather, sunlight. A direct beam of sunlight is an extremely high source of light as well as heat. Thus, direct sunlight as a light source needs to be minimized, while maximizing the use of diffused daylight. Excessive heat gain and ultraviolet damage to materials can be two negative results of daylighting that need to be balanced with the advantages gained from daylighting in a particular building. Glazing material can be selected to reduce both of these problems. Tinted glass though can block biologically important wave lengths and/or distort the color spectrum of daylight. Glazing should have high visible - light transmission (VLT) qualities and a low solar - heat gain coefficient (SHGC) for maximum daylighting benefits.

Glare is the biggest daylighting problem; it reduces the ability to see details. A school study of daylighting effects reported that glare from windows reduced test scores 15 to 25 percent. High contrast is created along with glare, either directly between the glazed surface and adjacent interior surface or indirectly where light falls on a surface. Daylight needs to be balance with light - colored interior surfaces to reduce the potential for these strong contrasts. Guidelines note that the window should not be more than 100 to 300 times as bright as the objects in the room. Furthermore, direct sunlight on task areas or reflected glare on television and computer screens can be avoided through orientation and shading. “ Daylight factor ” is a calculation used to compute the amount of daylight outside compared to a point inside.

One daylighting strategy involves “ harvesting ” light. The idea is to minimize direct sunlight penetration while maximizing daylight use. Integrating high ceilings and bringing in daylight from two directions help to increase daylight utilization. Sidelighting uses vertical glazing. For daylighting use, the glazing is located high on the wall or overhead, while vision or view glazing is positioned within a seven - foot distance from the floor.

Light shelves are a frequent addition to high lights or clerestories to increase the penetration of daylight further into the interior space. Continuous horizontal windows are better than individual windows or vertical ones. A light shelf facilitates deeper daylight penetration into a space, but it contributes even more to a uniform distribution of the daylight. A light shelf can also be effective in blocking direct sun at certain times of the year and day.

Toplighting is any daylighting delivered from the ceiling plane. This location for daylighting provides the potential for even distribution of daylight throughout a larger space and integrates well with electric lighting. Wall washing is possible with toplighting. Care in the design and placement of skylights is needed to avoid the problems of glare, excessive heat gain, and harsh contrast from direct sunlight. If toplighting is designed using deep wells and/or diffuse materials, these problems will be reduced. Sawtooth ceilings, light monitors, and north - facing clerestory windows, which were all popular in industrial settings a century ago, are effective ways to harvest daylight.

The following are Strategies and principles for effective daylight in interior spaces:

• Collaborate early with design team members to maximize building features that support daylighting.
• Provide soft, uniform light throughout the space.
• Provide thermal barriers for the windows to reduce heat gain or loss during unoccupied times.
• Use HVAC (heating, ventilating, and air - conditioning) to compensate for the additional radiation during daylighting hours.
• Provide glare - control and heat - gain shading systems.
• Orient a worker ’ s sight line away from windows, preferably with daylight coming from the side of a person. Rear lighting may produce shadows on the work material.
• Integrate automatic controls with a manual override for the shading system.
• Provide control mehanisms that adjust electric illumination when adequate daylighting is available. These include: on/off system, continuous dimming, and step switching or step dimming for individual ballasts and lamps .
• Use a closed - loop photosensor that reads electric light and daylight in preference to an open - loop sensor that reads only the daylight.
• Use an advanced lighting system with electronic ballasts to supplement daylight to maximize energy savings.

In developing an integrated daylight and electric light strategy, light levels from daylight need to be higher in a space than comparable light levels from electric light. The footcandle perception of the two is not equal. The IESNA suggests a rule of thumb: add 1 lumen of electric lighting for the loss of 2 – 3 lumens of daylight. While maximizing daylight use is an environmentally responsible strategy, electric lighting is a necessary supplement. Understanding and integrating daylight with electric light is important for achieving energy - effective and efficient electric lighting.