Section 12: Lighting

  1. Section 12

    Section 12

    12.1 Introduction

    This section provides guidance on specifying lighting for new and existing non-domestic buildings to meet relevant energy efficiency requirements in the Building Regulations. There are two alternative approaches, applicable both to systems in new buildings and to replacement systems in existing buildings.

    12.2 Scope of guidance
    The guidance in this section applies to the following types of lighting:

    • general interior lighting
    • display lighting.

    12.3 Key terms

    Office area means a space that involves predominantly desk-based tasks – e.g. a classroom, seminar or conference room.

    Daylit space means any space:

    a. within 6 m of a window wall, provided that the glazing area is at least 20% of the internal area of the window wall

    b. below rooflights, provided that the glazing area is at least 10% of the floor area.

    The normal light transmittance of the glazing should be at least 70%; if the light transmittance is below 70%, the glazing area should be increased proportionately for the space to be defined as daylit.

    Space classification for control purposes:

    Owned space means a space such as a small room for one or two people who control the lighting –
    e.g. a cellular office or consulting room.

    Shared space means a multi-occupied area – e.g. an open-plan office or factory production area.

    Temporarily owned space means a space where people are expected to operate the lighting controls while they are there – e.g. a hotel room or meeting room.

    Occasionally visited space means a space where people generally stay for a relatively short period of time when they visit the space – e.g. a storeroom or toilet.

    Unowned space means a space where individual users require lighting but are not expected to operate the lighting controls – e.g. a corridor or atrium.
    Managed space means a space where lighting is under the control of a responsible person – e.g. a hotel lounge, restaurant or shop.

    Local manual switching means that the distance on plan from any local switch to the luminaire it controls should generally be not more than 6 m, or twice the height of the light fitting above the floor if this is greater. Where the space is a daylit space served by side windows, the perimeter row of lighting should in general be separately switched.

    Photoelectric control is a type of control which switches or dims lighting in response to the amount of incoming daylight.

    Presence detection is a type of control which switches the lighting on when someone enters a space, and switches it off, or dims it down, after the space becomes unoccupied.

    Absence detection is a type of control which switches the lighting off, or dims it down, after the space becomes unoccupied, but where switching on is done manually.

    Lamp lumens means the sum of the average initial (100 hour) lumen output of all the lamps in the luminaire.

    Circuit-watt is the power consumed in lighting circuits by lamps and, where applicable, their associated control gear (including transformers and drivers) and power factor correction equipment.

    Lamp lumens per circuit-watt is the total lamp lumens summed for all luminaires in the relevant areas of the building, divided by the total circuit-watts for all the luminaires.

    LOR is the light output ratio of the luminaire, which means the ratio of the total light output of the luminaire under stated practical conditions to that of the lamp or lamps contained in the luminaire under reference conditions.

    Luminaire lumens per circuit-watt is the (lamp lumens  LOR) summed for all luminaires in the relevant areas of the building, divided by the total circuit-watts for all the luminaires.

    LENI (Lighting Energy Numeric Indicator) is a measure of the performance of lighting in terms of energy per square metre per year (kWh/m2/year), based on BS EN 15193:2007 Energy performance of buildings. Energy requirements for lighting.

    12.4 Lighting in new and existing buildings

    a. Lighting in new and existing buildings should meet the recommended minimum standards for:

    i. efficacy (averaged over the whole area of the applicable type of space in the building) and controls in Table 42


    ii. the LENI in Table 44. The LENI should be calculated using the procedure described in Section 12.5.

    b. The lighting should be metered to record its energy consumption in accordance with the minimum standards in Table 43.

    c. Lighting controls in new and existing buildings should follow the guidance in BRE Digest 498 Selecting lighting controls. Display lighting, where provided, should be controlled on dedicated circuits that can be switched off at times when people will not be inspecting exhibits or merchandise, or being entertained.

    ****Table 42   Recommended minimum lighting efficacy with controls in new and existing    buildings****

    ****Table 43 Recommended minimum standards for metering of general and display lighting in new****

    12.5 Lighting Energy Numeric Indicator (LENI)

    An alternative to complying with the efficacy standards in Table 42 is to follow the Lighting Energy Numeric Indicator (LENI) method.

    The LENI method calculates the performance of lighting in terms of energy per square metre per year. The approach described below must be followed in calculating the LENI for a lighting scheme. The LENI should not exceed the lighting energy limit specified in Table 44 for a given illuminance and hours run.

    Design the lighting

    The first step to energy efficient lighting is to design the lighting installation in a way that meets all of the users’ needs for the space under consideration.

    Recommendations for appropriate illuminance values and other lighting requirements may be found in BS EN 12464-1:201154, and in the Society of Light and Lighting (SLL) Code for Lighting. The SLL Lighting Handbook provides practical advice on how to design lighting for a number of different applications55.

    Look up the lighting energy limit

    In designing the lighting, a level of illuminance will have been selected as necessary for the tasks being done in a particular area. It is also necessary to determine how many hours per year the lighting will be needed. Once both the illuminance and the hours are known it is possible to look up the lighting energy limit in Table 44. For example, a classroom in a school may be lit to 300 lux and used for 40 hours per week for 39 weeks of the year, giving a total of 1560 hours per year. Values of 1500 hours and 300 lux give a lighting energy limit of 7.70. Table 44 also gives day-time (Td) and night-time (Tn) hour values which are used in the calculation of energy consumption.

    If display lighting is used, then the lighting energy limit may be increased by the value given for normal display lighting for the area of the room where display lighting is used. For example, in an entrance area for a building there may be some display lighting in a small area around the reception desk but not in the rest of the area.

    Shop windows use a lot of display lighting and may use up to 192.72 kWh/m2/year if the window faces a public road, and 96.8 kWh/m2/year if the window is in a shopping centre that is closed during the night.

    Calculate the parasitic energy use (Ep)

    If some form of lighting control system is used, then an allowance needs to be made for the energy used by the control system, and the fact that the luminaires take a little power even if they are dimmed down to give no light. An allowance of 0.3 W/m2 should be made for power used in this way. If the whole lighting system is switched off when the room is not in use, then the power loss is only during the hours of use. If the system is left on all the time then the power loss occurs for 8760 hours per year.

    If no lighting control system is used, then the parasitic energy use is zero.

    Determine the total power of lighting (Pl)

    This is the total power in watts consumed by the luminaires within a space.

    Determine the occupancy factor (Fo)

    Fo allows for the fact that energy is saved if an automatic control system detects the presence or absence of people in a room and switches off the lights when there is nobody using the room. If no automatic control is used, then the occupancy factor Fo1. If controls turn off the lights within 20 minutes of the room being empty, then Fo0.8.

    Determine the factor for daylight (Fd)

    Fd allows for the fact that if the lighting is dimmed down when there is daylight available, then less energy will be used. If no daylight-linked dimming system is used, then Fd1. If the electric lighting dims in response to daylight being available, then in areas with adequate daylight Fd0.8. Adequate daylight may be found in areas that are within 6 m of a window wall or in areas where 10% or more of the roof is translucent or made up of rooflights.

    Determine the constant illuminance factor (Fc)

    When lighting is designed, a maintenance factor (MF) is used to allow for the fact that as the lighting system ages it produces less light. This means that on day one the lighting system is providing more light than needed. Thus with a constant illuminance system, it is possible to under-run the lighting on day one, and then slowly increase the power used by the lighting until the point is reached when maintenance needs to be carried out by changing the lamps or cleaning the luminaires. Systems that control the lighting in this way have an Fc0.9, and those that do not have an Fc1.

    Calculate the daytime energy use (Ed)

    The daytime energy use is:


    Calculate the night-time energy use (En)

    The night-time energy use is:


    Calculate total energy (kWh) per square metre per year (LENI)

    The total energy per square metre per year is the sum of the daytime, night-time and parasitic energy uses per year divided by the area (A), as set out in the formula below:


    ****Table 44 Recommended maximum LENI (kWh per square metre per year) in new and existing buildings****