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Lighting Design Guide





Lighting Design 


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.

Glare

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. 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

Where:
L = length of room
W = width of room
Hm = height of luminaire above working plane


The result is used in conjunction with roomreflectance 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 = Fxnx N x MF x UF / A

Where:
E = average luminance
F = initial lamp lumens
n = number of lamps in each luminaire
N = number of luminaires
MF = maintenance factor
UF = utilisation factor
A = area

The maintenance factor is a multiple of factors and is determined as follows:

MF = LLMF x LSF x LMF x RSMF

Where:
LLMF = lamp lumen maintenance factor - the reduction in lumen output after specific burning hours

LSF = lamp survival factor - the percentage of lamp failures after specific burning hours

LMF = luminaire maintenance factor - the reduction in light output due to dirt deposition on or in the luminaire

RSMF= room surface maintenance factor - the reduction in reflectance due to dirt deposition in the room surfaces This can then be used as part of the calculation to determine the average illuminance level, using the following formula: The result is used in conjunction with room reflectance values to obtain a specific utilisation factor for the surface illuminated from the tables.

This article has been extracted from the "Lighting Design Guide" from Eaton




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