Part 2: Basics of sustainable lighting
In this second article of a two-part series, the author discusses how to balance environmental and economic concerns, architectural considerations, and human needs in sustainable lighting design.
Starting in 1990, some lighting professionals met with the U.S. Environmental Protection Agency and U.S. Dept. of Energy to represent the lighting professional’s perspective in the development of new energy standards and codes. Their work on energy addressed lighting quality issues that led to forming the Metrics of Quality Committee, which led to forming the Quality of the Visual Environment Committee, which in turn has led to some valuable research. The Illuminating Engineering Society of North America (IESNA) Sustainable Lighting Committee is a further enrichment of that effort.
IESNA’s “Sustainable Lighting Guide” will be released soon. A consortium of lighting organizations such as IESNA, American Lighting Assn. (ALA), and International Assn. of Lighting Designers (IALD) are collaborating with other organizations and agencies and are in the process of drafting a memorandum of understanding (MOU) designed to develop lighting quality criteria that will be included in the future editions of energy codes, sustainability codes, standards, and certification programs.
The purpose of lighting is to satisfy human needs; visibility; task performance; visual comfort; social communication; mood and atmosphere; health, safety, and well being; and aesthetic judgment. The role of the lighting designer is to match and rank the needs of the people using the space with economic and environmental concerns and architectural considerations. Lighting quality is achieved when the lighting design satisfies all three areas at once.
IESNA Lighting Handbook Chapter 10 and Design Guide DG-18-2006, “Light+Design: A Guide to Designing Quality Lighting for People and Buildings,” identify quality lighting as lighting that positively addresses human needs, architecture, economics, and energy and environment. A matrix is provided that can help designers identify which aspects to concentrate on for a given task. For example, for an office space with high ceiling height and intense computer use, the designer must consider the following issues:
- Task visibility (source/task/eye geometry and reflected glare): Position computer screens so that windows and other reflections are minimized on the screens. For under-cabinet lights, specify optical systems that minimize veiling reflections on shiny paper tasks. If the ambient light levels are low, provide a compact fluorescent or LED movable desktop task luminaire for areas of the desk not lighted by the under-cabinet luminaire. Design for recommended illuminance (horizontal and vertical) values.
- Visual comfort (discomfort glare and overhead glare): Block users’ direct view of bright lenses or bare lamps in task and overhead luminaires. Louvers and baffles are an effective way to block direct view of bare lamps from these angles. Provide window brightness controls.
- Aesthetic judgment (color appearance): Choose lighting and daylighting to be part of an appealing design. Use high color rendering index (CRI) lamp sources to ensure pleasant appearance of skin tones, clothing, and finishes. Use lamps with color temperature complementing with daylight.
- Mood and atmosphere: Use wall and ceiling brightness to create mood.
- Health and well-being: Consider circadian rhythms, which can be reinforced with daylighting.
- Light distribution on task plane (uniformity): Space the luminaires so that the illuminance pattern on the workplane is within the recommended uniformity range. Luminaire spacing can be increased if indirect or direct/indirect lighting is used.
- Light distribution on surfaces: Provide uniform illuminance on the walls, ceilings, and furniture partitions to reduce contrast and achieve visual comfort in the workplace. Indirect luminaires with some downward glow are recommended to reduce the contrast of an opaque luminaire against an illuminated ceiling.
- Room surface brightness: Interior work-spaces should have high reflectances (walls, 50% to 70%; ceiling, 75% to 90%) to make the space appear bright and cheerful and to increase inter-reflections and thus help reduce contrast of luminaires against their background. High reflectances also allow the designer to produce an effective lighted environment with less luminaires and thus conserve energy.
- Daylight and view: Use blinds or shades on windows to control glare and thermal discomfort from direct sun. Use high-reflectance walls to reduce the contrast between the bright windows and the walls. Provide overhangs, lightshelves, shades, blinds, or curtains to block direct view of the sun.
Economics and environment
- Energy: Use energy-efficient system components. (See “Part 1: Basics of sustainable lighting” in this magazine’s April 2010 issue for a detailed discussion.)
- Maintenance and change: Consider durability and maintenance issues. (See Part 1 for a detailed discussion.)
- Cost: This is a challenge. Generally, first-cost issues tend to favor less efficient, less appealing and higher maintenance solutions. Lifecycle cost analysis tends to favor energy-efficient, low-maintenance solutions. Human needs tend to favor more expensive, more appealing solutions.
Optimizing the use of daylighting
Daylight should be considered a primary light source in interior lighting systems. This is the first step in creating a lighting design that makes the most effective use of energy. It is also a highly regarded attribute of sustainable design, enjoyed by building occupants. Besides conserving energy, daylight can be a visually pleasant and comfortable environment that creates a positive atmosphere for our sense of well-being and productivity. Also, it gives the lighting designer a greater voice in the building orientation, window design, interior space configuration, and interior finish selections. We can rethink electric lighting as a supplementary source in a 3-D sense, not just design by reflected ceiling plan.
Here are a few general guidelines for good daylighting design.
Get involved early in the design process:
Using computer programs and physical scale models in the early stages of the integrated design process helps the designer to account for factors that influence day-lighig, such as locatin and climate, surroundings, orientation, opening position, and size (see Figure 1).
Use north- or south-facing windows:
Shade direct sun on south elevations. Shading is not necessary on the north. Low sun angles on the east and west are more difficult to shade and thus frequently contribute to unwanted heat gain and glare. Elongating the building in the east/west direction maximizes the opportunity for north and south windows and minimizes potential heat gain and glare. Horizontal overhangs work best for south windows; overhangs coupled with vertical landscaping (e.g., trees) work well for east and west elevations. Consider the occupancy schedule of a building when designing for daylight and sun control.
Introduce daylight high in the space and from two or more directions, if possible.
Design windows and skylights:
The overall thermal comfort and energy performance of a window or skylight depends on the exterior shading design and the characteristics of the glazing material and framing system. Good side-lighting designs differentiate view and daylighting functions by providing separate higher windows for ambient lighting and lower view windows. For view windows, high-performance glass (double-glazed units with a selective low-E coating) reduces heat gains and losses with minimal reduction in visible light. To minimize glare and heat gain, these view windows can be shaded by landscaping or exterior building elements. Top lighting, provided by skylights, produces two to five times the horizontal illuminance of a vertical window. However, on sunny days, intense direct sunlight can create glare and must be diffused, either by using diffuse material or by providing baffles and highly reflective light-wells under the skylight to control light delivery.
Bring in diffuse daylight to the ceiling and vertical surfaces: Reflecting daylight indirectly off the wall and ceiling surfaces and using diffusing materials in skylights spreads the light more evenly in the space, makes spaces appear larger, and evens out the daylight distribution. Means to achieve this include proper shading and glazing selection as well as light redistribution methods, such as prismatic panels and diffusing glass.
Address discomfort risks:
Well-daylit spaces can lose their performance when occupants forcibly use blinds or roll-down shades. Therefore, it is critical to provide a reasonable and user-friendly strategy for blinds with careful attention to glare, especially from direct line of sight of the sun.
Integrate electric lighting with daylight: Minimize the amount of electric lighting and enable electric lighting to respond to and supplement available daylight.
Provide variety in daylight levels: Use translucent covered walkways and entryways to gradually reduce the daylight level from the exterior to the interior. Although a base level of diffuse ambient lighting should be provided in all spaces, use localized higher daylight levels to generate variety and interest in selected spaces.
Light and health
While so much of lighting practice is focused on understanding how light affects our vision, we also know that light, as radiant energy, can affect our health and therefore our sense of comfort and well-being. Sustainable lighting design should consider the effect that lighting decisions have on human health.
There are at least five basic characteristics of light: quantity, spectrum, spatial distribution, duration, and timing. Light of enough quantity, of certain spectrum, applied at the right timing and for the right duration will affect the circadian system by suppressing melatonin at night and phase shifting the timing of the master clock.
Circadian rhythms are biological functions that repeat at approximately every 24 hr, including sleep/wake cycles, alertness, and hormone production. Circadian rhythms are generated and regulated by an internal master clock and are entrained or synchronized to the 24-hr solar day by external factors, most notably the light/dark cycle. For example, it has been found that light at night can suppress normal melatonin levels and distort sleep patterns.
In general, the research shows that humans need bright days and dark nights for normal sleep/wake cycles and melatonin levels. This forms an initial framework for practical applications where the circadian system as well as the visual system are considered in achieving good “lighting quality.” The exact positive and negative effects of light on the human health system outside laboratory conditions are still unknown. However, light’s effect on the circadian system of small populations has been observed both in laboratory settings and in real-life situations, for example:
- Benefits of daylight or sunlight penetration in hospital rooms have been shown to be effective at reducing patients’ hospitalizations, relieving stress, and decreasing analgesic use.1
- Bright light strategies and potential benefits include research findings indicating that bright light during the day will improve mood and behavior of dementia patients.2
- Lamp flicker, even when imperceptible, can cause eyestrain. Similar symptoms can be observed from glare.
- Exposing skin to light increases the manufacture of vitamin D and results in the absorption of calcium. Light in the short the wavelength range is used for the treatment of jaundice.
There is a big push for energy efficiency and reduction of carbon emissions. Lighting efficiency is definitely on the radar screen, with lighting retrofits being channeled into compact fluorescent lamps and new lighting systems considering the use of expensive but efficient LED luminaires. The new LED technology is a promising vehicle to achieve lighting that is energy efficient and healthier. Energy efficiency should not only consider the emission of photons (lumens/Watt) but also the benefits to human health.
However, our eagerness for energy efficiency is leading to an increasing disregard for human factors and the impact that energy efficiency measures will have on human health.
A quick, unofficial survey of many of the green buildings produced by the sustainable building movement underscores the need for more simplicity, beauty, and timelessness. We seem to be able to adequately express technology but have more difficulty creating something that lives up to our expectations when of it comes to comfort and aesthetics. For the future movement, we need to address and balance all these needs.
The human brain has two halves, left and right. While the left brain is analytical, detail-oriented and holds our survival skills, the right brain sees context and relationships, and holds our abilities to see “the whole” as well as the interconnectedness of the parts.
With energy efficiency on the left and human comfort on the right, the pendulum should swing between the two halves to create a balance, and that is the goal of sustainable lighting design.
About the author
Haran is an electrical and lighting consultant with his own private Chicago-area engineering firm. He has more than 20 years of experience in designing lighting and electrical systems for commercial, institutional, light industrial, and residential projects. He also is a member of Consulting-Specifying Engineer’s editorial advisory board.
1. Beauchemin K.M. and Hays, P., 1996, “Sunny Hospital Rooms Expedite Recovery from Severe and Refractory Depressions,” Journal of Affective Disorders. 1996 Sep 9;40(1-2):49-51.
2. Rixt F. Riemersma-van der Lek, MD, et. al. “Effect of Bright Light and Melatonin on Cognitive and Noncognitive Function in Elderly Residents of Group Care Facilities: A Randomized Controlled Trial.” Journal of the American Medical Assn. (JAMA), 2008; 299(22):2642-2655.
3. Wilkins, A.J., Nimmo-Smith, I.M., Slater, A. and Bedocs.