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ANNEX A - LIGHTING DESIGN PROCESS

Introduction to the Lighting Design Process

Applications for external lighting installations are often presented to local authorities in formats that make it difficult to appraise the overall lighting design, both visually and technically.

To improve the quality of both the design and of the information provided with the application a structured lighting design process should always be employed. When employing this design process detailed consideration should be taken to ensure that obtrusive light is minimised and that measures are taken to minimise the use of electrical energy. The lighting design process detailed in Table A1 can be employed for both large and small scale lighting designs. The stages in this process indicated as essential, are those that should be undertaken as the absolute minimum in order to achieve a compliant lighting design and provide the documentation essential for the submission assessment. By following this design process the lighting designer is encouraged to appraise any potentially negative effects of obtrusive light in conjunction during the development of the lighting design. This is in preference to the appraisal being carried out as a discrete study after the design has been finalised when it is often too late to make any alterations.

The lighting design process draws on technical information explained in other publications listed in the Bibliography and the stages of the design process form the index to this Annex. The design process follows the chronological order usual to a lighting designer's design stage methodology plan. Generally within each stage there is an explanation of the importance for the inclusion of each stage in the lighting design process and details of the lighting designers action and output required.

TABLE A1 LIGHTING DESIGN PROCESS

STAGE 1 - STATEMENT OF CLIENT NEEDS/OPERATIONAL STATEMENT (ESSENTIAL)

As part of this design process the lighting designer should establish and document the precise design requirements along with any local design constraints and to the greatest extent possible confirm the developer's overall lighting requirements. As part of this process the lighting designer should consider all the information required to prepare the operational statement described in paragraphs 27 and 28 of this Guidance Note. Any general lighting policy requirements of the local authority should also be determined at this stage and if necessary a preliminary submission should be made if the lighting project is large, or of an unusual nature or associated with a listed building or conservation area. Other affected external parties and special interest groups should be consulted at this stage.

The output of this process should list any issues that require to be addressed by the lighting design and by the operational statement. An operational statement should be provided with the submission.

STAGE 2 - SITE SURVEY (ESSENTIAL)

It is not unknown for a lighting design, for reasons of economy, to be conducted without the lighting designer ever having visited the development site. Even with a site survey it is not always possible to immediately identify all the potential lighting problems of an installation. Failure to carry out a site survey can create serious deficiencies in the lighting designer's overall understanding of the lighting environment and of what property and land will be impacted on by the proposed lighting installation. This lack of a site survey may place a risk on the designer with respect to the Construction Design and Management ( CDM) obligations and to other health and safety legislation duties.

The site survey is the starting point for a baseline study from which various visual and technical elements may be identified. This survey should include the location and identification of all existing lighting equipment in the area, in terms of equipment type and their wattages. This information is required to complete the requirements of Stages 3, 4 and 5. Additionally the survey should record site access restrictions which could have an effect or constraint on the intended lighting design and on the subsequent maintenance of the lighting equipment.

STAGE 3 - CRITICAL VIEWPOINTS (ESSENTIAL)

All new lighting installations will be overlooked by various parties and it is therefore essential that the lighting designer selects and considers the relevant viewpoints of these parties. When the lighting statement is carried out in conjunction with a landscape impact assessment then it is important to maintain the same critical landscape viewpoints from where the magnitude of the day-time visual impact of the new development will be quantified in non technical terms. By following the process in Stage 11 the lighting designer can quantify the visual aspects of the lighting in terms of the four or five measured or calculated light control values. However, luminaire orientation can sometimes provide different night-time visual priorities to those produced by day-time visual aesthetic techniques and it may be necessary to identify additional viewpoints or alternative installation options to address these night-time sensitive locations.

Residential properties close to new developments should always form the most important viewpoint and there are recommended illuminance levels on the night-time light levels that impinge on these properties. However, distant viewpoints, with a clear view of the development may require the need for glare limiting measures. It is often the magnitude of this light intensity, which provides the major source of complaint. If there is only one critical viewing direction then the lighting designer can use this to direct light away from the affected observer but not to the detriment of other viewpoints.

From each critical viewpoint the importance of each of the 5 light limitation values, viz. overspill; sky glow; light into bedroom windows; line of sight (source) intensity and overall building brightness, will vary relative to each of the different viewpoints and human interest. The inclusion of a Table of Importance in the lighting design submission, example shown in Table 3.1 below, will demonstrate the designers approach to visual risk analysis.

TABLE 3.1 EXAMPLE TABLE OF IMPORTANCE

STAGE 4 - EXISTING LIGHTING CONDITIONS

The assessment or measurement of existing lighting conditions has to consider both the lighting situation immediately adjacent to the application site and the general ambient luminance of the local area.

Existing Lighting Situation

Some light limitation values are based on maximum permissible limits. Lighting effects are accumulative and if an adjacent residential window illuminance has already reached its maximum recommended limiting value, then the new development should show that it has been designed to provide for a zero increase in illumination on that property. It is therefore inappropriate in an application to merely state that the limit will not be exceeded without stating the existing baseline criteria. The lighting designer should assume that there is no record kept of existing illuminance values and undertake the design relative to site measured or calculated levels.

Existing Ambient Luminance

Unless the local authority has produced a night-time environmental strategy plan it is necessary for the lighting designer to assess the existing ambient luminance condition of the area (see Stage 7) so that the control of stray light from the new design can be shown to be commensurate with and not exceeding existing conditions.

STAGE 5 - BASELINE CONDITIONS

To support the requirement of Stage 4 a baseline table showing calculated or measured values at defined locations should be prepared. If there is no existing lighting in the area prior to the new development being implemented there is no need to establish the baseline measurements.

When measurements, or calculations, are undertaken, values of illuminance should show whether they have been measured horizontally or vertically, providing their height from ground level.

STAGE 6 - TASK ANALYSIS (ESSENTIAL)

Most tasks have a particular lighting quality objective published as a recommended value but it is sometimes necessary to compare that task with other similar operations where there are no specific task recommendations. The essential point at this stage is to show that the lighting design quality objectives are not excessively high by comparing the design objectives with other similar task lighting recommendations.

An example of this can be found in the lighting for sports grounds where there are different lighting levels recommended for the playing of individual games. Applications often show the average illuminance that the design has achieved without declaring the playing requirement and thereby possibly using more energy than is needed.

The submission should clearly state the lighting quality objectives that have been complied with and the publication from which the lighting quality objectives were selected as detailed in Stage 8.

STAGE 7 - ESTABLISH ENVIRONMENTAL ZONE (ESSENTIAL)

The lighting designer shall require to determine the relevant environmental zone either by making reference to the local authority's lighting policy or by self assessment. Nationally recognised environmental zones are defined as follows, together with typical topographical areas:

The lighting designer should clearly indicate which zone has been selected together with the justification for selecting that zone.

STAGE 8 - LIGHTING DESIGN OBJECTIVES (ESSENTIAL)

This should take the form of a short section where the designer creates a technical picture of the predicted "lighting technical parameters" which the development will be designed to achieve. The lighting quality will be described in terms of illuminance (volume) and sometimes luminance (brightness) and should be compared with a professionally published recommended lighting quality objective.

The lighting designer has access to many sources of published data and should state the source document(s) from which the data used in his design has been extracted. A good design will compare lighting quality recommendations with other publications and equivalent task related recommendations when an exact task fit has not been found in published data.

STAGE 9 - LIGHTING DESIGN ITERATIVE METHODOLOGY

There is often more than one method of achieving the same lighting quality objectives and the lighting designer will often consider these different methods as a general assessment at the pre-design stage. The various options are often not considered worthy of documenting and only one option is normally presented in the application to assist in simplifying the approval stage. However, it is now important to show alternative considerations where there are electrical energy implications and this point is reinforced later (see Stage 13 - Designer's Critique).

For larger projects small areas are sometimes used for trial calculations to demonstrate typical lighting levels for different options. For each option the designer should be assessing the likely implications of potentially obtrusive situations. CIE Report 150:2003 has a section showing a matrix of known pitfalls and the benefits of different design options as a generalised flowchart.

This iterative process of design and appraisal can identify at an early stage any perceived weaknesses in the design, preventing the abortive work that could result should the obtrusive light reduction process be conducted at the end of the design process. Again the process of change as the design progresses is not often documented to avoid presenting a perceived weakness in the design methodology but if this is documented correctly it can show the local authority that external concerns have been allowed for and how the design has been constrained to accommodate the concerns.

STAGE 10 - CALCULATED PREDICTIONS (ESSENTIAL)

It is essential that all applications contain details of the light level calculations showing a horizontal grid of predicted values of not only for the task area but also for the overspill area beyond the site limits. There are many computer programmes available which can perform these two simple tasks but only a few have integrated the processes necessary to calculate potential obtrusive light impact values as outlined in Stage 11. In order to assist in visual recognition of the task area horizontal light overspill, relative to surrounding properties, the computer software should be able to import suitable mapping of the adjacent area and display this in conjunction with horizontal predictions.

Calculated assessments are normally based on laboratory measured intensity values radiating at various angles from the luminaire. Each luminaire has a unique photometric fingerprint of light distribution and calculated predictions are only correct for the particular luminaire make and type selected for the calculation. As indicated in paragraphs 29 and 30 care should therefore be taken at the installation checking stage to ensure that the same make and type of luminaire is installed as that proposed in the original design.

Substitute luminaires cannot therefore be assumed to produce the same fingerprint and consent should always be conditional on the luminaire type, mounting height, quantity, lamp type and wattage and luminaire orientation being as used in the prediction being maintained through to installation.

STAGE 11 - OBTRUSIVE LIGHT CALCULATIONS (ESSENTIAL)

The ILE Guidance notes and the CIE Report 150 provide lighting designers with national and internationally recognised technical limitations on obtrusive light levels. The design should therefore be carried out in conjunction with the monitoring of these calculated limits as an iterative process as the design progresses and not at its end when it may be too late to influence the final design. However, regardless of this point in time no application should be accepted which does not clearly outline the calculated values for all, or at least the first three, of the following items.

A Direct line of sight of the light emitted from luminaires is probably the principal source of obtrusive lighting complaints as it can produce the offensive glare effect that is referred to in the Introduction. This is light radiated directly from the luminaire where the limits quoted by the ILE and CIE relate to intensity values from individual luminaires when viewed from external view points into the site.

It is normal practice to calculate that the design mitigates the recommended limiting values, shown in the table below, from the critical viewpoints identified at Stage 3.

B Light intruding in through property windows can be predicted by calculating values on a vertical grid representing a window, or series of windows. The recommended limits are additive to what is already being experienced, pre development. If the pre development limits, shown in the table below, are already exceeded, the new design will require to show, by calculations, that zero light intrusion will be provided by the new development.

Both A and B above are essential elements in proving that the new development proposal will mitigate the majority of residents' concerns and in the case where the development requires the use of all night lighting the more onerous "post curfew" limiting values should be chosen as the maximum limit.

C The upward light ratio will vary between individual luminaires depending on the respective tilt angles and light distribution in their intended installed arrangement. Since the upward light ratio calculation is done for the complete installation the proposal application should state the individual luminaire elevations against which the calculation is based. Many quality luminaires produce a 0% upward light ratio at zero degrees of tilt but will produce an upward light ratio of 2.5% with 10º of tilt. Some luminaires can produce as much as 50% upward light ratio at tilt angles greater than 40º and if this was the case then the lighting installation could rightly be classed as being an obtrusive and inefficient lighting solution.

It should be remembered that the purpose of any lighting installation is to illuminate an area and will normally be projected downwards on to the desired area, be it road or area lighting. It is how this downward light is managed and its effects mitigated and controlled that are important: there will always be a degree of reflected upward light. Although the evaluation covers the direct upward component of light from the complete installation it does not include the light reflected upwards from the ground. Neither the ILE nor the CIE have defined or quantified this reflective element since no two developments have the same ground cover. As a general rule the darker the building or ground cover surfaces are, the lower the upward reflected component and conversely the lighter and wetter the building or ground cover then the higher the upward reflected component will be.

D The effect of glare, as viewed by an external observer, can be controlled by limiting the viewed intensity as described in A, however, sometimes it is necessary to carry out a second glare assessment with sports lighting to protect the interests of spectators and players. This calculation process is additional to that already carried out in A and is not a substitute evaluation.

E An additional glare evaluation may be required to protect the interest of all road users, including pedestrians and cyclists. The term Threshold Increment ( TI) has been used in street lighting quality assessment calculations for at least 15 years but its use is now being extended to ensure that vehicle drivers are not subjected to a threshold increment level greater than 15% from non-street lighting installations situated adjacent to a public highway. Again this is an additional assessment and is not a substitute for the requirements described in A and should be carried out as a cumulative process with the existing street lighting provision included in the calculation.

F Building luminance is normally only carried out for structures, which are architecturally transformed at night by the application of illuminating techniques. Different surface textures and colours reflect light in different proportions and any luminance calculation should include for a schedule of surface colours and reflection factor characteristics to be assumed in the calculation process.

G The calculation of the combined effects of direct and upward reflected light is generally unnecessary, and as stated in C, there are currently no national or international recommended limits on measuring success or failure with a proposed lighting design. It can, however, be used to good effect to demonstrate a visual comparison between the old and new lighting installation techniques. It can also be used to demonstrate the difference in upward reflections where new lighting has been designed in conjunction with landscaping techniques that soften their effect by reducing the area allocated to hard landscaping.

STAGE 12 - COMPARING DESIGN WITH BASELINE (ESSENTIAL)

A robust design methodology will carry out those assessments (Stage 11) as part of an iterative process during the formulation of the design. This iterative process involves providing trial assessments of the likely outcome of different lighting arrangements in small trial pockets within very large projects. In this way the impact assessment, in technically calculated magnitudes, can be formulated as the overall design progresses.

Since some of the light spill control values are based on cumulative lighting results, it is important to carry out calculations or take varied measurement assessments of the existing lighting arrangement to show that the new design overspill does not impinge or provide excess values when added to the existing arrangement.

Where an existing lighting arrangement has been calculated or measured to be providing excessively obtrusive light values but does not form part of the new development it may be judged unfair to over-constrain or penalise the new development for a previous generations' over-lighting techniques. However, it may be possible to encourage the new development to enlarge the scope of their lighting assessment to provide alternative arrangements for the existing lighting to reduce the overall impact when the combined lighting values are found to be over the obtrusive limit recommendations.

STAGE 13 - DESIGNER'S CRITIQUE

A robust design will have often considered different elements and applications during the formulation stage, and the application may only have the final version to approve or reject. In providing a critique the lighting designer can outline some or all of the lighting options, which have been considered together with the technical reasons for not progressing with some of these lighting options. This can assist the local authority in reaching a decision without referring the proposal back to the lighting designer with the request to try something different.

STAGE 14 - VIEWPOINT VISUALISATION

In addition to the calculations necessary to prove that the design does not produce obtrusive light towards the critical viewpoints the production of a lit environmental model can add visual simplicity to what can, for many, be a very complicated and technical presentation.

There are several visualisation software packages now available, however, the construction of an electronic model can be an expensive and labour intensive process and not all projects warrant this additional overhead cost.

STAGE 15 - VIRTUAL WALKTHROUGH

The production of a virtual walkthrough is the "icing on a cake" and can only be provided as a result of producing an electronic model of the installation as described in Stage 14. However, its main advantage is that different viewpoints, other than the critical ones, can be considered and "visualised".

STAGE 16 - SURFACE COLOUR SCHEDULE

All electronic virtual artwork relies on the construction of electronic model surfaces and some software produces very lifelike images. Lighting calculation software, which uses the light distribution fingerprint particular to an individual luminaire manufacturer's production model, does not have as wide a range of surface textures to visualisation software which has no lighting calculation facilities. Lighting calculation software relies on the designer creating a natural daytime colour match and a night-time reflection factor to create the model.

A general analysis of the electronic model surfaces should be provided in the form of a schedule containing all the surface colours, in terms of the general colour description, the red/yellow/blue co-ordinate reference and the light reflection factor characteristics.

At the application stage this information is not essential to illustrate compliance with most common light control analysis but it does become important when the building luminance requires to be analysed. It also becomes important in demonstrating which version of the colour scheme has been used in the design calculations, particularly so where building material changes have been made during the structure design stage.

STAGE 17 - LUMINAIRE SCHEDULE (ESSENTIAL)

The luminaire schedule forms an essential element in both the approval and the subsequent construction stage of the development. The schedule should contain, as a minimum, the seven items listed below which determine the luminaire's potential performance in terms of the following:-

A - Luminaire light distribution type and bowl type (often included in a manufacturer's catalogue number).

B Lamp type and wattage.

C Mounting height.

D Orientation direction (between 0º and 359º with 0º relative to a declared point in the development plan. Some software calculation algorithms use North and others use East as 0º but all use an anti-clockwise direction as the angle increases).

E Luminaire tilt (between 0º and 90º and the greater this angle the greater the potential for producing obtrusive light in the form of viewed intensity and upward light ratio).

F Lamp position (optic setting).

G Type of control gear.

With some calculation software the orientation and tilt are given as a composite X,Y,Z co-ordinate relative to the main calculation grid, e.g. on a sports field, and this sometimes makes it difficult to make a quick visual assessment of the luminaire orientation and elevation relative to distant property outside the site boundary. Most software calculation processes have an automatic conversion process and although the designer may have used an X,Y,Z co-ordinate to accurately aim each floodlight, relative to the playing surface, the software can automatically convert this 3-dimensional number into a 2-angle notational representation of the same positional aim without additional design work. The 2-angle system is easier to visualise at the application appraisal stage.

STAGE 18 - ENERGY USAGE (ESSENTIAL)

There is currently no government legislation covering the limitations on the electrical load for external lighting installations, equivalent to that which exists in Building Regulations for new interior lighting projects. However, there are two values that can be utilised to indicate the efficiency of a proposed lighting installation.

1. The first and foremost being the electrical load distributed over the area of the site in watts per square metre. This value is likely to become the key measurement of the installation efficiency in the same way that the current Building Regulations attempt to limit the use of less efficient light sources.

2. The second value may be the total lamp lumens per square metre of development in an attempt to prove that the use of less distribution efficient luminaires has been mitigated in the design.

Neither of these two methods directly demonstrate obtrusive light mitigation and should not be used in isolation since their main function is to show an energy control factor. An example of recent landmark projects results, using luminaires with high quality light control, are shown in Table 18.1 below. Budget priced luminaires will often return higher watts per square metre.

Table 18.1 Energy monitor target examples

The lighting designer should review the market place to ensure that the most efficient luminaire, control gear and lamp are employed to minimise the watts/ square metre required to provide the required lighting level.

STAGE 19 - SCHEDULE OF LUMINAIRE PROFILES

On large projects it is often necessary to utilise different types of luminaire to light specific areas effectively and efficiently, however care should be taken to limit a proliferation of design types throughout the design.

The luminaire schedule should provide pictorial images together with design reference numbers, manufacturer's catalogue numbers and a cross reference to the luminaire schedule prepared as part of Stage 17.

Luminaire manufacturers usually produce composite data sheets for their luminaire range but this can sometimes be too general to be included in an application and are not precise enough to itemise exact model and beam distribution proposed for each luminaire type included in the design.

STAGE 20 - LAYOUT PLAN (ESSENTIAL)

This is the last item of the 20-point design process and is essential for presenting accurate details of the proposed lighting equipment layout. It is not the only information that should be provided and it is essential that the layout plan be submitted along with all other information indicated throughout the design process. The layout plan is another form of visualisation as far as the application is concerned and it is important to include details of the surrounding landscape, property and existing lighting arrangements to assist in creating a more comprehensive picture that indicates that the developer and lighting designer have considered the baseline lighting conditions and that the new lighting proposal minimises possible obtrusive light.

The layout plan should show the new column and luminaire positions together with a reference number for each location necessary to provide a relationship with the luminaire schedule described in stage 17 and each luminaire orientation should be shown by an extended line from the mounting location. The location and details about all other lighting equipment should be indicated on the layout plan together with any other details that may be specifically required by each local authority.

SUBMISSION STAGE

When the developer/lighting designer has prepared all essential information as indicated in the design process the Lighting Design Check List in Annex B should be completed to indicate what is included in the application submission package. The number of copies required shall be specific to each local authority.

ANNEX B - LIGHTING DESIGN CHECK LIST

ANNEX C - LIGHTING INSTALLATION CHECK LIST

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