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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

scheduled maintenance.

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.

Energy Efficiency

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.

Special Considerations

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

be produced.

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

the tables.

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

as follows:




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

each luminaire

N = number of luminaires

MF = maintenance factor

UF = utilisation factor

A = area