“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.
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.
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 AdvancedBuildings.org.
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.
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.
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
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
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.
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
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
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.
fixture lengths when practical to reduce cost. Longer is better, says
one manufacturer. Specify a 12-ft. length instead of three 4-ft. units
Aim for uniform
brightness on all surfaces throughout the space while achieving maximum
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