Lighting considerations in lab planning and design; the right choice of fixtures and controls can significantly improve user productivity while reducing operating expenses.
Decades of lighting research demonstrate the importance of effective lighting on worker well-being and performance. This is especially true for laboratories because they are such intense work environments; the quality of the environment is just as important as the functionality. Therefore, successful design solutions must help reduce glare, gloom, and visual fatigue to support worker satisfaction and productivity.
In the 1970s and '80s, the most commonly used lighting system in laboratories was the direct-source 2- x 4-ft recessed light fixture that used four fluorescent lamps in a recessed fixture with an acrylic prismatic lens. Newer installations replaced the prismatic lens with the parabolic troffer. While the parabolics tended to reduce the glare experienced on computer screens, most recently, architects and engineers are using either indirect or indirect/direct luminaires to mitigate the effects of cave lighting and glare, and they are integrating the lighting solution with the overall design of the space.
Today's challenge, then, is to plan and design spaces that make the most of energy-efficient design strategies and meld daylighting, renewable energy sources, and sustainable construction practices. The U.S. Dept. of Energy's FEMP group has developed a program called "Energy Effective Lighting," and while it is focused on saving energy and improving workspaces for federal workers, their guidance and recommendations are applicable to any work environment. In general, the idea is to balance ambient lighting with task lighting and to balance daylit sources with electrical sources.
Effective, integrated design solutions should include the following issues:
* Room surface brightness.
* Reduction of glare.
* Adequate task illuminance.
* Uniform light distribution.
* Appropriate lamp color and ballasts.
* Visual interest and variation.
* Energy-efficient lamps.
* Controls and integration with daylighting.
* Luminaire maintenance.
Room surface brightness
The overall brightness of a room is greatly influenced by the illuminance and reflectiveness of the horizontal and vertical surfaces. Traditionally, designers have focused on the required footcandles needed for a space; however, the lightness of the walls, ceiling, and partitions also affects the perceived brightness of a space. As such, it makes sense to balance illumination of both horizontal and vertical surfaces. Wall washing with downlights or locating troffers near the wall to raise the wall brightness help reduce the high contrast of generally lit spaces.
Reduction of glare
Direct glare and veiling reflectance from overly bright lamps and reflectors can cause significant visual discomfort. In downlight locations using compact fluorescents, the use of cross baffles will provide shielding from the glare. The downside of using open-bottom luminaires (such as parabolics) is that some worker spaces will be exposed to the bare lamp.
While most manufacturers will recommend using T-8 lamps in parabolic luminaires, glare can be avoided by using semi-specular or mare surfaces for lighting fixtures and room surfaces. In this case, specular reflectors or louvers should not be used because they reflect the bright image of the lamp into the eyes of the occupant. Therefore, use semi-specular louvers or white reflectors. VDT screens should be oriented away from glare sources and windows or provided with low-glare screens. A uniform wash of light at the ceiling also helps because the contrast between the light and the ceiling is avoided.
Adequate task illuminance
The goal here is to provide the quality and quantity of illumination needed for the scientists to accomplish their work. In general, even with ceiling-mounted luminaires (whether providing indirect, direct, or indirect/direct lighting), most workspaces need additional illumination at the worksurface. Sometimes an under cabinet task light is provided, but it is not generally that effective because it provides too much light from the wrong direction. An alternative solution may be to provide the task lighting from the side or specify that the lights have low-output ballasts. While reducing output and energy consumption by about 50%, such a fixture will also deliver adequate task lighting and reduce the under-cabinet shadow. Another idea would be to provide articulated task lighting that would allow the use to adjust the light source according to the task at hand
The National Institutes of Health's design guide lines specify that laboratories should have lighting levels of approximately 80 footcandles. For surface mounted lighting, they recommend wrap-around type diffusers. Lighting should be located parallel to the bench surface, along a line directly over the front edge of the bench top. This arrangement eliminates any shadow or reflection that might interfere with bench-top procedures.
Design criteria, however, should not dwell exclusively on footcandles. Luminance ratios and surface brightness may be more important factors than just how many footcandles are reaching a given work surface. Each space needs to be an integrated design solution that balances the light once it hits surfaces walls, floors, and ceilings.
Uniform light distribution
The uniformity of light distribution depends on variety of factors: distribution of the ceiling fixtures type of ceiling fixture, and geometry of the space There should be a balance of light at the bench, along the aisle, and at the room perimeter. Since labs have so many upper cabinets, tall refrigerators, fume hoods, incubators, freezers and the like, it may make more sense to use more fixtures with lower outputs. Each manufacturer specifies a certain Space Criteria for given fixture, and while this value needs to be factored into the initial lighting layout, it doesn't account for the addition of myriad tall cabinets, equipment, or upper casework.
Traditionally, in wholly open-plan offices, designer have used a Space Criteria factor of 1.5 times the distance from the desk to the ceiling. In other words, h an office with 9-ft ceilings and a desk height at 30-in. (2.5 ft), the spacing between ceiling lights would be 1.5(9 - 2.5), or 9.75 ft apart. Use of this equation has translated to designing lighting layouts for labs, but often the resulting distance does not correspond very effectively with current modular planning for labs and the lighting gets off-module with the worksurfaces below. Therefore, the maximum center-to-center lighting placement should respond to the modular layout selected for the casework and equipment.
Whether indirect or direct, the layout of the luminaires should provide wall brightness at the top of the wall and uniformity at the work surface, and the design should avoid glare that is either direct or reflected. In order to avoid the cave effect and disquieting high brightness contrast, wall-washer fluorescent lighting e can be located at the room edge, and the 2x4 troffer layout can start closer to the edge of the actual work-space. Laboratories tend to suffer file cave effect simply due the location of upper cabinet units that effectively channel the light into the benchwork aisles. This condition is exacerbated when the tops of upper cabinets also become long-term storage locations for supplies (even though a code requirement stipulates that nothing shall be within 18-in of the ceiling).
Whatever the furniture system selected, the layout and configuration need to reflect the window placement as well as the luminaire placement above.
Appropriate lamp color and ballasts
Many users have disliked fluorescent lamps because of their traditionally poor color rendition. Newer models have much better color rendering, and the selection of these lamps can be specified to suit a certain color index. Look for a CRI (Color Rendering Index) of 70 or more. Cooler lamp colors may work better in the high-intensity light conditions of the lab, while in most offices intermediate-temperature colors work better. So if the office and lab are adjoining spaces, there needs to be some middle-ground selection of light color or some other type of transition, because an abrupt color contrast between cool and intermediate can be disquieting.
Another complaint about fluorescent lamps stems from ballast flicker and hum. While there is no conclusive evidence, research has shown a decrease in headaches and improved visual performance with the use of electronic ballasts.
Unless there is sensitive electronic equipment in use, stay away from magnetic ballasts.
Visual interest and variation
Most lab environments include huddle spaces or corridors that provide excellent opportunities to creatively express the difference in space function or corridor location. This can be done with decorative wall-washer sconces, cove lighting, or downlights.
Throughout the 1970s, manufacturers of fluorescent lamps introduced new products that were designed to use less electricity than the traditional 40-Watt fluorescent tube. While they saved on energy, they also lacked the same light output. However by the 1980s, the T-8 lamp was introduced, and it has since become the standard for new construction. It is also a popular retrofit replacement for the T-12 lamp. The "T-8" designation refers to the diameter of the tube in eighths of an inch; therefore, the T-8 is a 1-in.-diameter tube. The T-12 is a 1 1/2-in.-diameter tube. However, given the characteristics of fluorescent luminaires, the T-8 actually provides more light output. The T-8 lamp is an excellent replacement lamp for T-12s because they are more efficient. Additionally, the T-8s operate at a lower wattage and therefore produce less heat.
In fluorescent lamp technologies, the smaller lamp diameters have greater surface brightness. As such, the most efficient lamps have also the greatest intensity. However, this can be uncomfortable to the naked eye because they are just too bright, and so this aspect needs to be addressed during design. The newer T-8 fluorescent lamps should be used with open-cell parabolic fixtures, while T-5s, which offer excellent energy efficiency, should be limited to indirect or wall washing applications. (T-5s have the same output as T8s.)
Compact fluorescent lighting (CFL) is quickly replacing incandescent lighting (such as for task lights) because it can save up to 80% in energy costs without sacrificing lighting quality. The average compact fluorescent light bulb lasts up to 10X longer than its incandescent counterpart. CFLs got off to a bad start in the industry because originally they had very bright and unnatural light, and they hummed. But their technology is vastly improved, and they provide quick savings on energy bills, lower cooling costs, and require less maintenance.
Controls and daylighting
Automatic light controls should be considered as part of energy-efficient design strategies because they can save significant amounts of energy over time. Such controls include:
* Occupancy sensors.
* Daylight harvesting (also known as load shedding: the use of daylight-based controls to adjust lighting according to availability of natural light).
* Lumen maintenance and tuning.
* Sweep-off lighting schedule with overrides. With sweep-off lighting, controls systematically turn off lights floor by floor or zone by zone at preset times when tenants are not likely to be present.
* On-demand personal dimming.
Toilet rooms, conference rooms, and some lab equipment/support rooms would be good candidates for lighting control via occupancy sensors, while sweep-off lighting might work for general lab spaces in facilities that are not occupied round-the-clock. This discussion needs to be included in the early design stages to integrate controls into the planning and design of the space.
Control system selection should ensure compatibility with lamps and ballasts. For example, HID lamps should use bi-level ballasts in combination with occupancy sensors. There are also photocell products available that can dim lights based on the amount of day-lighting available in a space.
However, it can be difficult to find fluorescent fixtures that provide cost-effective and reliable dimming capabilities. Only 4-pin compact fluorescent lamps with advanced electronic ballasts can be dimmed. Fluorescent lamps that operate on a longer burning cycle (when they stay on all day) also tend to have a longer life cycle. Thus, a fluorescent lamp that may be rated for 20,000 hours may burn out sooner if occupancy sensors control them.
The NIH Design Guidelines recommend using T-8 lamps with programmable lighting controls and local override switches. These fluorescent luminaires also need to use electronic ballasts. The NIH specifics ultrasonic-type controls for enclosed rooms and passive infrared for offices.
Once construction is complete, lighting controls need to be included in the building commissioning so that users and maintenance personnel understand how to use them correctly and effectively.
Because so many lab projects involve low-budget renovations, it is important to understand how effective luminaire maintenance can support the design solution. First of all, effective lighting maintenance goes a long way toward ensuring the energy efficiency of any lighting system. Maintenance plans should include relamping and periodic cleaning of lamps because this can prevent the loss of light and forestall the deterioration of the lamp fixture. Improper cleaning materials or techniques can also damage the lens surface. For example, aluminum finishes should not be cleaned with strong alkaline cleansers. Plastics really attract dust, so if your lab has acrylic troffers, you might replace them or remove them for cleaning twice a year.
Light output from lamps decreases over time, but periodic relamping and replacement ballasting can forestall complete luminaire replacement. Consider retrofitting T-12 lamps using magnetic ballasts with T-8 lamps using electronic ballasts. Dark walls and floors require more power to produce the same amount of light, so if rehabbing labs, consider refinishing surfaces to produce better light reflectance.
The EPA sponsors a Green Lights program for retrofit projects. This program provides a lot of good recommendations for retrofit lighting projects, and it can be found on the EPA website (www.epa.gov; search for "green lights").
* Keep light reflectance' of surfaces that are visible at eye level and above as light-colored as possible, preferably at 65-75% for walls and 80-95% for ceilings.
* Use a wall-washing system, or locate a wall-wash troffer close to the wall to raise wall brightness.
* Use semi-specular or white-finish louvers in the luminaires. Avoid narrow spacing and coordinate with bench tops and equipment locations below.
* Provide indirect light at walls (sconces or wall washers) to balance the contrast between the bright window light and the interior wall. Avoid harsh patterns, lighting scallops, and shadows at the tops of walls.
* Provide visual interest by varying the lighting at circulation nodes and room entries.
* Avoid the use of under-cabinet lights that produce a direct view of the lamp from the workstation.
* Avoid orienting PC monitors to windows.
Definitions for Some Commonly Used Terms
Ambient, task, wall wash, and accent fighting. Lighting designers typically separate lighting into four categories: ambient, task, wall wash, and accent. Ambient lighting provides security and safety as well as general illumination for performing activities. The goal of task lighting is to provide enough illumination for performing a specific task, but it does not provide general illumination of a space. Wall wash lighting illuminates wails so that they blend more closely with the naturally bright areas such as ceiling, Accent lighting creates emphasis or highlights a specific object or spot.
Lumen. The measurement of light output from a lamp, most commonly referred to as a bulb or tube.
Illumination. The distribution of light on a horizontal surface, measured in footcandles. The amount of illumination required varies according to the visual acuity required to perform a task comfortably and without eyestrain. For example, the Illuminating Engineering Society recommends that 30 to 50 footcandles is adequate for most home and office work.
Lighting types. There are four basic types of lighting: incandescent, fluorescent, high intensity discharge (HID), and low-pressure sodium:
* Incandescent lighting is most commonly used in residential construction. While incandescent lighting is the least expensive to buy, it is mot inefficient than other lighting types, and it is also the most expensive t operate. Newer types of incandescent bulbs provide greater efficiencies, and they include tungsten halogens, reflector lamps, and PARs (parabolic aluminized reflectors). The far more efficient compact fluorescent bulb is replacing incandescents, even in some residential settings.
* Fluorescent lighting is most commonly used in indoor commercial applications. Fluorescent lighting can be used for both task and ambler applications, and it is more than 3 to 4X more efficient than its incandescent counterpart. However, to be most efficient, these lights need to be on for several hours at a time. Fluorescents also need ballasts that control the electricity and provide the starting and circuit protection. Fluorescents are available as compacts fluorescents (CFLs) and tube fluorescents.
* HID lighting is used only for outdoor applications or in high-ceiling spaces such as atriums. This group is divided into metal halide, mercury vapor, and high-pressure sodium products.
* Low-pressure sodium lighting is used where color rendering is not important, such as highway, warehouse, utility, and security locations. They are the most efficient artificial lighting devices and have the longest service life. However, they render all color as yellows or grays.
* Environmental Design + Construction magazine. ("Searchable Product and Resource Guide" at www.edcmag.com; "Compact Fluorescent Lighting", 1/30/2001; "Lighting Tips From the Pros", 1/16/2001.)
* National Lighting Product Information Program, Rensselaer Polytechnic Institute Lighting Research Center, www.lrc.rpi.edu/nlpip. ("Guide to Selecting Frequently Switched T-8 Fluorescent Lamp Ballast Systems"; "Lighting Answers Series: T-8 Fluorescent Lamps.")
* Pacific Gas and Electric Co., www.pge.com. ("Energy Tips for Business.")
* Federal Lighting Guide, A Resource for Federal Lighting Improvement Projects, June 1998.
* National Institutes of Health, NIH Guide to Laboratory Design, "Design Policy and Guidelines, Draft," Office of Research Services, Dec. 18, 1995.
* U.S. Dept. of Energy, Office of Energy Efficiency and Renewable Energy. ("Consumer Energy Information, EREC Fact Sheets," http://www.eren.doe.gov/consumerinfo/factsheet.html.)
* U.S. Dept. of Energy, Office of Federal Energy Management Programs, FEMP Lights, http://www.eren.doe.gov/femp/ (click on "resources" then "lighting resources"). ("Benefits of Energy Effective Lighting for Offices"; "Economics of Energy Effective Lighting"; "Energy Effective Lighting Checklist")
* U.S Dept. of Energy, California Energy Commission, and Electric Power Research Institute.
* "Advanced Lighting Guidelines: 1993, Final Report." (National Technical Information Service, www.ntis.gov.)
* U.S. Environmental Protection Agency/Dept. of Energy, "Laboratories for the 21st Century" conference, NREL, December 2000.
Victoria David, AIA, is a principal with Maynard/ David Partnership Inc., Denver (www.maynarddavid.com). Maynard/David Partnership is an architecture and planning firm specializing in, and exclusively serving, the advanced technology community.
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|Title Annotation:||Chapter 5: casework, floors, lighting|
|Publication:||R & D|
|Date:||Nov 1, 2003|
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