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Health, Photobiological Response

Vision and Non-Visible Light

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Spectral eye sensitivity curves for the cone system shown with the solid line (V2) and rod system shown with the dotted line (V1). Source: Van Bommel, 2004[1]. Permission Pending.
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Spectral biological action curve for the non-visual system (Bλ) based on melatonin suppression in comparison to the visual sensitivity curve (Vλ). This highlights that the non-visual system has a different sensitivity range than the visual system; it is shifted into the blue range of the spectrum, therefore, is more sensitive to longer wavelengths than the visual system. Source: Van Bommel, 2004[1]. Permission Pending.
Visual and biological pathways in the brain. Nerve connections between the retina and brain are discretely different between visual and non-visual systems. The visual system connects the cones and rods to the visual cortex (represented with a continuous bold line) and the non-visual system is connected from the novel receptor in the retina to the suprachiasmatic nucleus and pineal gland (represented by the dotted line). These discrete systems and pathways underscores the importance of understanding the role that light has on both visual and non-visual systems. Source: Van Bommel, 2004[1]. Permission Pending.

Light has a significant impact on our quality of life, and impacts our perception of a quality environment. Most research to date has focused on our visual response to light and its affect on our functional vision and task performance. Recent discoveries in photobiology, however, highlight the fact that daylight also has a significant impact on human health. In 2002 a novel, nonvisual, photocell was discovered in the human eye (Berson 2002). Bodily rhythms and systems are regulated primarily through these retinal ganglion cells through exposure to light and dark cycles. Thus, our eye is mediating two parallel responses to light: one for vision and one for physiological regulation. The non-optical retinal ganglion receptor is connected through its own pathway through the superchiasmatic nucleus in the brain, and triggers a multi-synaptic light induced pathway that communicates to other nonvisual parts of the nervous system. This process acts as a clock, oscillating on daily (circadian) and seasonal (circannual) rhythms.

Many physiological responses are activated and regulated by light entering the eye and triggering these non-visual photoreceptors. For example, body temperature and the hormones cortisol and melatonin are regulated through this process. These two hormones play important roles in governing alertness, sleep, regulating blood sugar, and maintaining the immune system. An imbalance in these hormones over a long period of time exhausts the system causing fatigue, stress, and loss in the body’s homeostatic balance. In a natural setting where we have access to natural light, the body synchronizes its internal clock to the changing nature of sunlight. In environments where we have less access to natural light, these biological systems can be disrupted significantly. In a recent study of nurses, night shift work has been associated with increased risk for cancer (Dimich-Ward, 2007). This suggests that lack of light or exposure to light at times of day that we have not adapted to over thousands of years can have a powerful negative effect on our health and is potentially very toxic over a long period of time.

The biggest architectural implication for light and human health is designing buildings that create as much opportunity for accessing daylight as possible. Our non-visual system has evolved to respond to natural light, thus it is critical to provide spaces that work with the natural rhythms of the environment and allow occupants access to natural light. Maintaining true darkness is also critical to these natural rhythms. Control of electric lighting at night in order to create true darkness is key to maintaining natural rhythms. For example, limiting the amount of light that ‘leaks’ from corridors into sleeping rooms, limiting amount of equipment glow in rooms, and properly shading windows are all critical for creating true darkness at night.

Section Key Resources
  • Berson, D.M., Dunn, F.A., Takao, M. (2002). Phototransduction by retinal ganglion cell that set the circadian clock. Science, 295: 1070-1073.
  • Dimich-Ward, H., Lororenzi, M., Teschke, K., et. al. “Mortality and Cancer Incidence in a Cohort of Registered Nurses from British Columbia, Canada.” American Journal of Industrial Medicine 50 (2007): 892-900.
  • Figueiro, M., Brainard, G., Lockley, S., Revell, V., White, R. “Light and Human Health: An Overview of the Impact of Optical Radiation on Visual, Circadian, Neuroendocrine, and Neurobehavioral Responses.” Illuminating Engineering Society of North America, 2008.
  • Joseph, Anjali. The Impact of Light on Outcomes in Healthcare Settings. Concord, CA: The Center for Health Design, 2006.
  • Van Bommel, WJM and GJ van den Beld. “Lighting For Work: A Review of Visual and Biological Effects.” Lighting Res. Techol. 36.4 (2004): 255-269.
  • No links specific to this section have been listed.

Lead Author(s): Heather Burpee

Psychological / Psychophysics/ Perception vs Metrics

Perception of light quality is subjective and does not always match more quantitative measures of light quantity.

Luminance, Illuminance, Brightness

Luminance measures the amount of light traveling in a given direction and is often measured in candela per meter square (cd/m2). Luminance is often used to describe the light emission or reflection from a surface. It indicates how much light will be perceived by the eye looking just at that surface. Illuminance is a measure of the incident light on a surface per area and is often measured in lux or lumens per meter square. Illuminance has been referred to as brightness, but brightness is actually a subjective perception of the magnitude of visual light.

Perception of Brightness

The perceived brightness of a surface is directly related to the brightness of surrounding surfaces. Luminance measures this in isolation, however, visual perception takes into account the entirety of a space, not just the luminance on a single surface. Thus, light balance on multiple surfaces can significantly influence the perception of brightness in a space.

Practical implications

Spaces that have surfaces with balanced luminance will be perceived as brighter than ones that have surfaces that have highly variable luminance. This is true even if the light intensity in the second is greater overall. Thus, spaces that balance the amount of light will appear brighter. As an example, a classroom that is only side-lit will appear darker than one that is both side-lit and back-lit with a skylight – even if the overall luminance of the surfaces is lower in the second space. That is because the balance of light. We perceive the second room as brighter because the back wall that is washed with light from the skylight, which balances the light coming in the windows on the opposite wall. Overall the light in the space is balanced, and our eye perceives the room as bright. The first room appears dark because there is a large difference in the amount of light coming from the window and the amount of light that is on the back wall. Overall that contrast of luminosity translates to a perception of darkness at the back of the room.

Section Key Resources
  • Ghosh, K., Bhaumik, K. (2010). Complexity in Human Perception of Brightness: A Historical Review on the Evolution of the Philosophy of Visual Perception. OnLine Journal of Biological Sciences 10 (1): 17-35, 2010.

Lead Author(s): Heather Burpee


Enhanced individual or organizational productivity and satisfaction can be measured in a multitude of ways and can be influenced by various factors. The quality of interior environment, such as increased daylight is one attribute that can have a positive influence on these human factors. Boyce outlines three routes where daylight can influence human performance: through the visual system, through the circadian system, and through the perceptual system.

Visual Performance

Improved vision and performance of visual tasks is the starting point for staff productivity. The amount, distribution, and spectrum of the light are all integral to providing the best lighting conditions. Electric light can be used for tasks, but it has been shown that in critical tasks involving color discrimination, balanced daylight is the best source of light (Boyce, 2003).

Circadian Effects

Light/dark cycles also have been shown to influence productivity. A shift in the natural circadian clock for night shift workers has been shown to increase performance creating greater alertness at times of natural sleepiness. However, long-term disruptions in this natural circadian clock have been attributed to decreased productivity and disease. Studies have shown that nurses that consistently work during the night shift have an increase in several chronic diseases, are less productive, and less alert on the job, which may result in errors (Booker, 1995; Horowitz, 2001; Smith-Coggins, 1997). These studies also point out the implication to day-shift workers who never see the light of the day during their shifts. Overall, daylight during the day and true dark at night are effective in entraining positive human circadian rhythms, which correlate to human health and performance.

Perceptual System

Perception of daylight in work environments is an important consideration to performance. Negative perceptions due to glare and visual discomfort can diminish productivity and positive reaction to daylight. There is a strong perceptual preference for workplaces with windows and views, but the impact of these windows on mood depend on individual preference and expectation. Also, there is little understanding of how mood impacts performance.

Positive Impacts

Daylight and views have been attributed to faster healing times for patients (Ulrich, 1984), increased satisfaction for employees (Veitch, 2002), and increased sales for retailers (Heschong-Mahone 1999). These all have positive financial implications for organizations’ bottom-line.

Section Key Resources
  • Berson, D.M., Dunn, F.A., Takao, M. (2002). Phototransduction by retinal ganglion cell that set the circadian clock. Science, 295: 1070-1073.
  • Booker, J. M. , Roseman, C., . (1995). "Seasonal Pattern of Hospital Medication Errors in Alaska." Psychiatry Research. 57:251-257.
  • Boyce, P., Hunter, C., Howlett, O. (2003). The benefits of daylight through windows. Troy (NY): Lighting Research Center.
  • Heschong-Mahone Group (1999). “Skylighting in Retail Sales: An Investigation Into the Relationship Between Daylighting and Human Performance.” Sacramento, CA: Pacific Electric Company.
  • Horowitz, T. S., Cade, B. E., et al. (2001). "Efficacy of Bright Light and Sleep-Darkness Schedule in Alleviating Circadian Maladaption to Night Work." American Journal of Physiology -- Endocrinology and Metabolism. 281:384-391.
  • Smith-Coggins R, Rosekind MR, Buccino KR, Dinges DF, Moser RP. (1997). “Rotating shiftwork schedules: can we enhance physician adaptation to night shifts?” Academic Emergency Medicine. 4:951-61.
  • Ulrich, R.S. (1984). "View Through a Window May Influence Recovery from Surgery." Science. 224:420-421.
  • No links specific to this section have been listed.

Lead Author(s): Heather Burpee

High levels of illumination available from daylight

Visual Performance, Daylight and View

Vision and performance of visual tasks is clearly the starting point for staff productivity. The amount, distribution, and spectrum of the light are all integral in providing the best lighting conditions. Artificial light can be used for tasks, but it has been shown that in critical tasks involving color discrimination, balanced daylight is the best source of light (Boyce, 2003).

Error rates are decreased in well lit environments. A study of pharmacists showed a decrease in dispensing errors, from 3.5% to 2.6%, when light levels were increased from 450 lux to 1500 lux (Boyce, 2003). Also, error rates were shown to increase among nurses in Alaska during the winter months vs. the summer months showing a correlation of error rate and daytime light exposure (Booker, 1995).

Evidence also suggests that views of natural environments are more conducive to productivity and have calming effect. Physiological manifestations of viewing a natural spaces such as water, greenery or flowers are measurable within five minutes of viewing such a scene. Stress responses are decreased: blood pressure, heart activity, muscle tension, and brain electrical activity (Ulrich, 1981; Ulrich 1991). “Because natural views tend to produce positive responses, they may be more effective in reducing stress, decreasing anxiety, holding attention, and improving mood (Edwards, 2002).” Views to the outside also provide more focal variety and distance of focal length, thereby reducing eye strain over the course of the day. Varying depths of focus are important in maintaining visual agility, and views to the outside aide in providing variety and depth of field.

It is difficult to extract the positive benefit of daylight vs. the positive benefits of views. Connections between windows, daylight and view are inherently intertwined in the perception of space. Positive attributes from each are difficult to isolate since they are so intricately intertwined. What is known is that both are important to create productive, healthy interior environments.

Section Key Resources
  • Begemann, S., van den Beld, G., Tenner, A. (1997) Daylight, artificial light and people in an office environment, overview of visual and biological responses. International Journal of Industrial Ergonomics 20(1997) 231-239.
  • Berson, D.M., Dunn, F.A., Takao, M. (2002). Phototransduction by retinal ganglion cell that set the circadian clock. Science, 295: 1070-1073.
  • Booker, J., Roseman, C. (1995) A Seasonal Pattern of Hospital Medication Errors in Alaska. Psychiatry Research 57(1995) 251-257.
  • Boyce, P., Hunter, C., Howlett, O. (2003). The benefits of daylight through windows. Troy (NY): Lighting Research Center.
  • Carmody, J., Selkowitz, S.E., Lee, E.S., Arasteh, D., Willmert, T. (2004). Window Systems for High-Performance Buildings. New York: Norton & Company.
  • Edwards, L., Torcellini, P., et al. (2002). A Literature Review of the Effects of Natural Light on Building Occupants (Technical Report). National Renewable Energy Lab. Golden, CO.
  • Ulrich, R.S. (1984). View Through a Window May Influence Recovery from Surgery. Science. 224:420-421.
  • Ulrich, R. S. (1991). Effects of Health Facility Interior Design on Wellness: Theory and Recent Scientific Research. Journal of Health Care Design, 3 (1991): 97-109.
  • No links specific to this section have been listed.

Lead Author(s): Heather Burpee

Page Key Resources
  • No publications general to this page have been listed.
  • No links general to this page have been listed.
  1. ^ a b c W.J.M. van Bommel. Non-visual biological effect of lighting and the practical meaning for lighting for work. Applied Ergonomics 37 (2006) 461–466
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