Effects of Natural Light on Building Occupants

Authors

Paul Torcellini and L. Edwards

Abstract

Effects of Natural Light on Building Occupants A Literature Review
by Paul Torcellini, Senior Engineer and L. Edwards

This publication is a report prepared as an account of work sponsored by an agency of the United States government (U.S. Department of Energy). It presents summary information from a noncritical literature review on daylighting in buildings. It was the goal of this document to compile a listing of the literature that is commonly cited for showing the impacts of daylighting in buildings. The report is an excellent documentation for the effects of daylight with regard to health, safety and human performance. The report is available for sale to the public, in paper from U.S. Department of Commerce National Technical Information Service. (http://www.ntis.gov/ordering.htm)

The main topics of the report are:

4. Affects of Light on the Body How the Eye Works Affects of Light on Internal Body Systems Nervous and Endocrine System Circadian Cycles Medical Cures from Light Rickets and Osteomalaci		5. Daylighting in the Office Health in the Office Productivity in the Office Absenteeism in the Office Employee Turnover Financial Savings Employee Preferences and Perspectives Improper Daylighting
6. Daylighting in Schools Health Attendance Achievement Perspectives Financial Benefits: Costs of Absence/Student/Day Breakdown Windowless Classrooms Testimonials from Windowless Classrooms		7. Daylighting in Retail Problems for Retail Daylighting 8. Daylighting in Health Care Facilities Benefits for Patients and Workers Post-Surgical Results Healing Environment
9. Daylighting Industrial Environments Physiological Effects Psychological Health Productivity and Safety		10. Conclusion

Presentation

1. Background

This paper presents summary information from a noncritical literature review on daylighting in buildings. It is by no means exhaustive, and no attempt has been made to determine the scientific nature of the studies that are cited. It was the goal of this document to compile a listing of the literature that is commonly cited for showing the impacts of daylighting in buildings. NREL does not endorse any of the findings as the citations have not been critically reviewed.

Many building owners and architects have reported energy savings received from daylighting.
Looking at the energy consumption of commercial buildings in the United States demonstrates the importance of saving energy. According to the Department of Energy’s Office of Building Technology, State and Community Programs (BTS) 2000 Databook, commercial buildings consumed 32% of United States electricity in 1998, of which 33% went to lighting. Not only is electrical lighting responsible for a significant amount of the electrical load on a commercial building, but it can also cause excessive cooling loads. Utility costs for a building can be decreased when daylighting is properly designed to replace electrical lighting.

Along with the importance of energy, studies have demonstrated the nonenergy related benefits of daylighting. Quantitative studies and qualitative statements are used to summarize the use of daylighting in buildings, its effects on occupants, and its potential economic benefits. Data have been compiled from books, periodicals, Internet articles, and interviews. The books, periodicals and Internet articles provided the background information necessary to identify the main subjects of the paper. Interviews provided details related to specific buildings and companies that have integrated daylighting into their building.

Daylighting data have been divided into Wavelengths of Light, The Affects of Light on the Body, and the following building sections: offices, schools, retail, health care, and industrial. The sections Wavelengths of Lights and The Affects of Light on the Body help describe the impact daylight has on building occupants. Each building section includes the effect daylight has on the building occupants psychologically and physiologically. Economic data have been cited in the categories in which information was found.

2. Introduction

Before the 1940s, daylight was the primary light source in buildings; artificial lights supplemented the natural light. In the short span of 20 years, electric lighting had transformed the workplace by meeting most or all of the occupants’ lighting requirements. Recently, energy and environmental concerns have made daylighting a rediscovered aspect of building lighting design. The physics of daylighting has not changed since its original use, but the building design to use it has. Daylighting is often integrated into a building as an architectural statement and for energy savings. However, benefits from daylighting extend beyond architecture and energy. The psychological and physiological aspects of natural light should also be considered. The comforting space and connection to the environment provided to building occupants provide benefits as significant as the energy savings to building owners and managers.

This paper summarizes the benefits that different wavelengths of light have on building occupants. Daylighting has been associated with higher productivity, lower absenteeism, fewer errors or defects in products, positive attitudes, reduced fatigue, and reduced eyestrain.

3. Wavelengths of Light

Electrical light sources include cool white fluorescent, incandescent, energy-efficient fluorescent, and full-spectrum fluorescent lighting. Each type has a different level of energy consumption. However, the most important factor affecting building occupants is the different spectrums of light that each source produces (see Appendix).

Different wavelengths or spectral distributions of light have different effects on the human body. Most electrical light sources lack the spectral distribution needed for complete biological functions, although full-spectrum fluorescent lighting does come close to that of natural light (Hathaway, et al. 1992).

Cool white fluorescent lights are concentrated in the yellow to red end of the visible light spectrum. Incandescent lamps, similarly, are concentrated in the orange to red end of the spectrum. In comparison, energy-efficient fluorescent lighting is typically concentrated in the yellow to green portion of the spectrum. These three light sources lack the blue portion of the color spectrum (Liberman 1991), which is the most important part for humans and is best provided by natural light. Full-spectrum fluorescent lighting is the electrical light source that has a spectrum of light most similar to natural light because it provides light in the blue portion of the spectrum.

Daylight provides a better lighting environment than cool white or energy-efficient fluorescent electrical light sources because “daylight…most closely matches the visual response that, through evolution, humans have come to compare with all other light” (Franta and Anstead 1994). The majority of humans prefer a daylit environment because sunlight consists of a balanced spectrum of color, with its energy peaking slightly in the blue-green area of the visible spectrum (Liberman 1991). According to Hathaway, et al. (1992), natural light also has the highest levels of light needed for biological functions:

The photobiologic action spectra of greatest importance to humans ranges from 290 to 770 nanometers. Skin reddening and vitamin D synthesis occurs in the range of 290 to 315 nanometers. Tanning or pigmentation of the skin and reduction of dental…[cavities] occurs in response to band light in the band from 280 to 400 nanometers. Vision is the most sensitive to light in the 500- to 650- nanometer range (yellow-green light). Billirubin degradation occurs in response to light in the 400- to 500-nanometer range (blue light) (Hathway, et al. 1992).

4. Effects of Light on the Body

Humans are affected both psychologically and physiologically by the different spectrums provided by the various types of light. These effects are the less quantifiable and easily overlooked benefits of daylighting. Daylighting has been associated with improved mood, enhanced morale, lower fatigue, and reduced eyestrain. One of the important psychological aspects from daylighting is meeting a need for contact with the outside living environment (Robbins 1986).

According to Dr. Ott (Ott Biolight Systems, Inc. 1997a), the body uses light as a nutrient for metabolic processes similar to water or food. Natural light stimulates essential biologicalfunctions in the brain and is divided into colors that are vital to our health. On a cloudy day or under poor lighting conditions, the inability to perceive the colors from light can affect our mood and energy level. Dr. Liberman (1994) also mentioned that light plays a role in maintaining health:

When we speak about health, balance, and physiological regulation, we are referring to the function of the body’s major health keepers; the nervous system and the endocrine system. These major control centers of the body are directly stimulated and regulated by light, to an extent far beyond what modern science…has been willing to accept.

A 1986 study by West as cited by Heerwagen (1986) evaluated the effects of light on health by evaluating prison inmates with different window views. He found that inmates with windows facing a meadow or mountains had significantly lower rates of stress-related sick calls than inmates with a view of the prison courtyard and buildings. Furthermore, inmates on the second floor had lower rates of stress-related sick calls compared with inmates on the first floor.
Reasons for the differences in sick calls included a more expansive view from the second floor, which provided increased positive psychological benefits. Inmates on the first floor had added stress from lack of privacy because of visibility to passersby.

Because natural views tend to produce positive responses, they may be more effective in reducing stress, decreasing anxiety, holding attention, and improving mood. Studies in 1979, 1981, and 1986 by Ulrich (Heerwagen 1986) support the effectiveness of natural views. Ulrich found that viewing vegetation and water through slides or movies is more effective in creating psycho-physiological recovery from stress than built scenes without water or vegetation. Also, individuals recovered faster and more completely from a stressful event when exposed to films of natural settings as opposed to urban scenes. Nature group subjects also had lower muscle tension, lower skin conductance, and higher pulse transit along with possibly lower blood pressure from these health differences. Furthermore, Ulrich reported more positive emotional states and wakeful relaxation states for people exposed to natural scenes.

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