CA452001EN - March 2015
Lighting Design Guide
Designing a basic lighting scheme requires the consideration of
many factors, not just the achievement of a desired lighting level.
Basic objectives must first be established, such as:
– What sort of tasks will be performed in the area?
– What ‘mood’ needs to be created?
– What type of lighting will create a comfortable environment?
There are also standards and legislation that need to be complied
with. For example:
– How energy efficient must the lighting be?
– How will Building Regulations affect the design?
– Is emergency lighting required?
When all of these objectives and requirements have been
established, they can be expressed as a series of lighting criteria
in order to facilitate a quality lighting design. Criteria that would
normally be considered are:
Level of Illumination
Illumination levels for a wide variety of environments and tasks
can be found in BS EN 12464-1: 2011 and the Society of
Light and Lighting’s Code for Lighting. The levels stated are
maintained illuminance, which is the minimum average
illumination level that should be achieved at the point of
Uniformity and Ratios of Illuminance
The combination of luminaires selected should evenly
illuminate the working plane and appropriately illuminate walls
and ceilings in relation to the task illumination, so that a
pleasant and comfortable environment is achieved. In specific
areas, increased directional lighting may be required to create
a defined or more intimate environment.
The acceptable level of glare should be established as
appropriate for the application, using information in
BS EN 12464-1: 2011 and the SLL Code for Lighting.
Colour and Room Reflectance
The colour appearance of the lamps should be chosen for
the application and complement the interior colour scheme,
which should be chosen with an appreciation of the reflectance
values that will be achieved. Lamps should be selected with
appropriate colour rendition properties as detailed in EN12464-1
and for colour discrimination and reduction of eye fatigue.
Luminaires should be selected that meet the requirements of
the Building Regulations Part L. The distribution characteristics
should also match the requirements of the criteria above.
Certain applications require additional considerations, such
as the addition of display lighting, the arduous nature of the
environment or the use of Display Screen Equipment.
Luminaires should be selected and the design completed with
these elements in mind, where appropriate.
After these criteria have all been considered, a lighting scheme
calculation can be undertaken. The most popular method of
establishing the quantity of luminaires required, the illumination
level achieved and the luminaire layout, is to use computer
software created specifically for lighting design. It is important
to remember that all the criteria above must still be considered
prior to using computer software, if a satisfactory scheme is to
Lighting design can also be achieved using published photometric
data, such as that included on the product pages of this catalogue.
Average illumination via the lumen method of calculation can
provide fast results that can then be assessed and facilitate more
detailed design of the most appropriate option if required.
Lumen Method Calculations
This method uses the utilisation factor tables created from
photometric measurement of each luminaire. Firstly, the Room
Index (K) of the space must be calculated, which is the relationship
and measure of the proportions of the room:
K = L x W
(L + W) x Hm
The result is used in conjunction with room reflectance values to
obtain a specific utilisation factor for the surface illuminated from
This can then be used as part of the calculation to determine the
average illuminance level, using the following formula:
E = F x n x N x MF x UF
The maintenance factor is a multiple of factors and is determined
= LLMF x LSF x LMF x RSMF
LLMF = lamp lumen maintenance factor - the reduction
in lumen output after specific burning hours
= lamp survival factor - the percentage of lamp
failures after specific burning hours
= luminaire maintenance factor - the reduction in
light output due to dirt deposited on or in the
RSMF = room surface maintenance factor - the
reduction in reflectance due to dirt deposition in
the room surfaces
Guidance on calculating each of these factors is provided in the
SLL Code for Lighting. Alternatively, contact our Technical Support
and Application Department for advice.
Finally, the luminaires must be spaced in the room such that
acceptable uniformity is achieved. The maximum spacing to
height ratio, SHRmax, provides the maximum spacing permissible
between luminaires in both transverse and axial directions, in
comparison to the mounting height and should not be exceeded if
acceptable uniformity is to be achieved.
L = length of room
W = width of room
Hm = height of luminaire
above working plane
E = average illuminance
F = initial lamp lumens
n = number of lamps in
N = number of luminaires
MF = maintenance factor
UF = utilisation factor
A = area