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Although lighting calculations can be performed manually, the process demands a high number of man-hours. Software solutions like DIALux speed up the process.
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DESIGN | ELECTRICAL ENGINEERING | LIGHTING DESIGN
A well-designed lighting system provides just the right amount of light for its
intended application: less lumens yield poor performance, but more lumens
represent wasted energy. Like in any building system design, the optimal
capacity can only be specified with an adequate calculation procedure.
Lighting designers use the photometric data of proposed fixtures as a
starting point. For the calculation procedure they consider the project’s
location, indoor or outdoor, as well as environmental conditions like
temperature and dirt.
The purpose of lighting calculation is to reach a suitable illuminance level
for the intended application. The concept of illuminance describes lighting
delivered per unit of area, and it is typically measured in foot-candles
(lumens per square foot) or lux (lumens per square meter). In the case of
New York City, meeting the lighting efficacy requirements of the NYC Energy
Conservation Code is also important.
Illuminance levels for each location are not arbitrary; they are established
by industry organizations such as IESNA (Illuminating Engineering Society
of North America). When specifying a lighting system, design engineers
aim for the illuminance values established in the IESNA Lighting Handbook.
Achieving the exact specified values is not feasible, but a lighting design is
satisfactory if the variation is slight.
Make sure your lighting system meets
IESNA and NYC codes.
Lighting calculations can be carried out manually, but this approach
demands considerable man-hours and is impractical in modern building
design. A more effective approach is using automated software
calculations, allowing the lighting designer to focus on the best decisions,
while a computer handles repetitive tasks.
The lighting design specialization is available for professionals from
different backgrounds. For example, architects, electrical engineers and
interior designers all have a knowledge base that is suitable to complement
The Lumen Method: Basic Lighting
The lumen method provides a simple hand calculation approach to
estimate the illumination achieved with a proposed lighting distribution. The
method becomes impractical for complex room geometries or very large
projects that are split into multiple areas. It can be summarized in the
•Calculate the Room Cavity Ratio (RCR): The RCR describes the
ratio of vertical area to horizontal area in a room. The RCR formula
varies depending on room geometry.
•Obtain surface reflectance: The reflectance is the fraction of light
reflected from a surface, and it is strongly influenced by texture and
colour. Reflectance values are required for ceilings, walls and floors.
•Obtain photometric data: When you purchase a lighting product, its
specifications include total lighting output and its spatial distribution.
This is fundamental information for lighting calculation procedures.
•Determine the Coefficient of Utilization (CU): Based on the RCR
and surface reflectance, it is possible to determine the CU, which
indicates how efficiently the lighting output is delivered to the working
plane. The CU is obtained from tables in the IESNA Lighting
Handbook, and it is also known as Utilization Factor (UF).
•Calculate the Maintenance Factor (MF): The maintenance factor
accounts for lighting fixture degradation over time, as well as dirt
accumulation. Deterioration and dirt reduce the lighting output, and
illuminance falls below the specified level over time if their effect is
not accounted for.
•Use the Lumen Method Formula: There are two ways to apply the
formula. It can be used to calculate the number of luminaires required
to reach a given illuminance value, or vice versa - calculating the
illuminance that results from a given number of fixtures.
The lumen method formula is provided below:
E = Required illuminance
n = Lamps per luminaire
F = Lumen output per lamp
CU = Coefficient of utilization
MF = Maintenance factor
The advantage of the lumen method is simplicity, only requiring basic room
data and luminaire data. However, it only provides an average illuminance
value that does not reflect variations for different parts of the room. In other
words, it is impossible to predict if there are excessively illuminated areas
or dark spots.
Overview of DIALux
Although there are many lighting design software packages available,
DIALux has the advantage of being free while remaining a powerful design
tool. Instead of selling the software to lighting designers, they charge
lighting manufacturers to have their products on the DIALux database with
photometric data and 3D models. This simplifies the design process, since
there is no need to search for photometric files of the proposed fixtures.
DIALux can adapt to a wide range of project conditions, ranging from
individual rooms to complete buildings, as well as outdoor locations. The
software can also account for daylighting through windows. Architectural
files from common formats like DWG (AutoCAD) can be imported, avoiding
tedious file conversions.
method is that software determines lighting variations in the area being
analyzed, while the lumen method provides the average value. This allows
adjustments to the lighting design when some areas are too bright or too
dark, which is not possible with the lumen method. DIALux represents
these illuminance variations both in 2D plans and rendered 3D models of
the space being designed.
Lighting design software is useful not only in new constructions, but also
when renovating existing spaces. For example, if LED lighting will be
deployed to reduce power bills, a software analysis can be used to
determine if lighting quality will be high - energy efficiency should not come
at the expense of performance.
What Are the Ideal Lighting Parameters
Office buildings represent a significant percentage of total built area in New
York City, which means that a lighting designer will probably work on these
projects frequently. To achieve the best results, the following parameters
500 lux or more
19 or less
0.6 or more
80 or more
If your property is covered by Local Law 88 of the Greener Greater
Buildings Plan, you must upgrade your lighting by 2025 to meet the NYC
Energy Conservation Code. Working with qualified lighting designers
Department of Buildings.
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