Specifying Design Lighting

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Display Lighting on BRUKL

SBEM and DSM have three input methods for lighting:

• Unknown
• Chosen
• Design

1. UNKNOWN

The unknown option allows you to select a specific lighting technology and SBEM will assume an efficacy (efficiency in lumens/watt) for that technology. It assumes a 'worst case' efficiency and is not suitable for building regulations. For both EPCs and Building Regulation calculations it is best to use one of the other options for input provided you have actual data to specify using those options. The values assumed are listed in the table below (from NCM Modelling Guides England 2021, Scotland 2022, Wales 2022). 

Note 

• the efficacy includes any losses due to absorption of emitted light by the luminaire.
• 'Top-Lit' refers to activities that are typically tall spaces using roof lights for example warehouse storage, retail warehouses, sports halls.

2. CHOSEN

If you know the specific lighting product that is installed then you can use the luminaire manufacturers data (luminaire lumens/watt and Light Output Ratio) as input. Note the Lamp type is only used for filtering EPC recommendations in this case. You can also use this specification method even if you have Design Calculations, though, if that is the case, you must also supply the Design Illuminance:

This method enables you to check Building Regulation compliance without running a SBEM / DSM calculation: 

125 * 0.9=112.5

112.5 ≥ 95 (95lm/W minimum efficacy for 2021 / 2022 regulations)

3. DESIGN

If a Design calculation has been produced, the Design option may be used. The W/m² figure should not include the consumption for controls (constant illuminance, daylight, occupancy). These should be input in the relevant parasitic power dialogue. The standard illuminance (300lux in this case) is assumed if a value for Design Illuminance is not input. However, if you are using actual design calculations, these should include a design lux and this must be input. Note that Design calculations should use a Maintenance Factor (0.8) to represent the degradation in light output over time. This factor is automatically applied to 'Chosen' and 'Unknown' inputs.

It is generally advantageous for the lighting design to have a design lux below the NCM maximum illuminance for the activity. If the illuminance is above the NCM maximum then the Notional Building lighting will use a lighting spec (95lumen/watt) based on the NCM maximum illuminance. This is likely to make it more difficult to achieve a BER < TER. If you're inputing using the 'Chosen' format then temporarily switch over to 'Design' to check what maximum illuminance you should ideally not exceed.

NCM Design calculation

There is an inbuilt algorithm for Lighting Design calculations in SBEM. This algorithm will convert 

• a 'chosen' (or 'unknown') input into a W/m2 input for the energy / CO2 calculation. 
  • lm/W -> W/m²
• a 'design' input into a Luminaire lm/W output for the BRUKL report.
  • W/m² -> lm/W

Separate Lighting Design calculations using software specifically for that use will be much more sophisticated than the calculation performed by SBEM. Such software will model the lighting distribution from the luminaire, model detailed geometry and reflective properties of internal surfaces. Such software will produce a different result to SBEM, sometimes a better result than SBEM, sometimes a poorer result than SBEM. Thus if you input the W/m²  for a Design you will likely get a different lm/W to that recorded on the Design report.

DSM uses the same algorithm as SBEM for converting luminaire data to W/m² and vice versa.