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MEEF - Middle East Economic Engineering - Articles    previous page


Description: “Linear indirect” is a broad term used to describe suspended and wall-mounted light fixtures that emit most or all light in an upward direction. Light reaches users indirectly—that is, after being reflected from ceilings and walls. The fixture may be indirect (100 percent upward distribution), semi-indirect (90-100 percent up), or direct-indirect (70-90 percent up).

The result of indirect lighting is a space that may feature more balanced brightness and visual comfort, reduced glare and resulting eyestrain, and energy savings. Popular applications now include private and open-plan offices, educational facilities, laboratories, libraries, training rooms, multipurpose spaces, conference rooms, corridors and common areas.


Energy Savings: Indirect lighting designs can save energy compared to traditional direct lighting schemes. Linear indirect lighting, specifically using T5HO lamps, is more energy-efficient than a typical T8 direct system, according to manufacturers.

Indirect lighting enables shifting the role of task illumination to task lighting located where these tasks are preformed, and reducing the role of the general lighting system to providing sufficient lighting for orientation.

Indirect lighting also provides more uniform lighting, which allows for a reduction in light levels that in turn translates to fewer fixtures and energy savings, according to

Importance of Visual Comfort: The modern definition of productivity has expanded to encompass job satisfaction and intent to turnover. A 1987 study in the Journal of Applied Psychology reported that workplace characteristics account for as much as a 31 percent variance in job satisfaction. A 1997 American Society of Interior Designers (ASID) study determined that 68 percent of workers complain about the light in their offices. A 1991 Steelcase survey conducted by Louis Harris & Associates discovered that 44 percent of office workers and 64 percent of computer users considered eyestrain (due to glare) to be the leading hazard to their health in the office.

Following this logic chain backwards, if visual comfort can be improved and glare reduced through improved lighting, workers may become more satisfied with their workplace, which in turn may lead to improvements in productivity and reduced turnover. The latter studies also suggest that the construction industry may not be satisfying 44-68 percent of office workers with provided lighting systems.

According to manufacturers, indirect lighting can improve visual comfort by reducing eyestrain and glare in offices, classrooms and similar spaces. They say that properly designed indirect lighting systems can help architects meet IESNA/ANSI recommended practice for office and educational spaces.

Major Trends: Just 10 years ago, indirect lighting systems were often considered visually uninteresting, difficult to specify and install, expensive and restricted to ceilings with ceiling heights of 10 ft. or higher. Manufacturers say this category has matured considerably since then. Competition and growing market acceptance have led to lower costs, standardization resulting in simplified installation, shorter lead times, better packaging, and broader and deeper product lines.

Although budget is always a challenge, product costs have declined in the last five years, making linear systems more affordable. One manufacturer estimates that the average cost of linear lighting has declined as much as 70 percent in the last 7-8 years. In addition, linear lighting systems require fewer fixtures and fewer power-drops in a given space. As a result, the upfront fixture costs may be more but the installed cost will be comparable to non-linear systems in some applications.

Indirect lighting has also become more compact and less obtrusive due to growing adoption of T5 and T5HO lamps. The high intensity of T5HO lamps means that rows of indirect fixtures can be placed as much as 12-15 ft. apart on ceilings as low as 9 ft. and provide uniform illumination on the ceiling. This can result in fewer fixtures required than typical T8 fixtures, which typically require 10-12 ft. spacing and higher ceilings.

For those applications where T8 is a better option, high-output T8 lamps (3100 lumens) and electronic ballasts offering flexible levels of light output are now available.

Today’s linear indirect fixtures are now often specified with a downlight component and a luminous element, such as perforations or luminous panels, to highlight the fixtures and provide a more balanced blend with a luminous ceiling.

Improved optical systems are enabling linear fixtures to perform well at an 18-in. suspension length, suitable for many 9-ft. ceilings and even 8.5-ft. ceilings with certain lamping options.

Some manufacturers are now offering linear fixtures integrated with automatic controls such as controls and sensors to provide personal dimming capability to occupants as well as opportunities for facilitywide dimming.

Specification Tips: All manufacturers advise lighting practitioners to prioritize visual comfort and glare, get educated about indirect lighting as a solution, share that education with the owner, write a detailed performance spec, and find the right product that matches the budget and project needs without reverting to parabolic troffers as an immediate reaction to cost limitations. Manufacturers also offer these tips:

Select a high-performance lighting system, pay attention to the location of the runs—whether they are perpendicular or parallel to the workflow, select primary fixtures from a single manufacturer, and stand by your specification.

Remember that good lighting design is not just about light levels. Consider other lighting quality metrics such as lighting walls and keeping uniform levels throughout the space.

Be careful in specifying fixtures with too much downlight. The more direct light, the greater the chance of debilitating glare.

Consider longer fixture lengths when practical to reduce cost. Longer is better, says one manufacturer. Specify a 12-ft. length instead of three 4-ft. units joined together.

Aim for uniform brightness on all surfaces throughout the space while achieving maximum energy efficiency.

On top of specifying the product itself, also specify that runs of linear lighting are joined cleanly and remain straight over the entire length without any visible sagging.


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