Engineering Inputs

Akshay Padwal avatar
Written by Akshay Padwal
Updated over a week ago

Lighting is one of the major contributors to the internal heat gains and energy use of the building. Most energy codes set the maximum amount of lighting energy consumption in terms of Lighting Power Density (LPD). The platform automatically loads the defined maximum LPD when you select the energy code from the Project page. Important point to note that if the model is exported from drawing.tool, then the area-weighted average of applied templates is populated. More details can be found in this article.

The platform automated LPD values are referred from ASHRAE Standard 90.1 Table 9.5.1 or the IECC Table C405.3.2(2) for your code version. If a specific local code is selected (e.g. Title 24 for the State of California), then that code manual is referenced to automate the LPD input.

Lighting (W/ft2) | (w/m2): This is an automated input by the platform based on the maximum LPD value. This value varies based on the building type and the energy code version. This value can be modified if additional information about the project is known.

Additionally, the hourly profile can easily be adjusted by a dedicated lighting schedule.

Details about how the daylight and occupancy sensors work are explained in the attached articles. There is an additional factor included in lighting EUI calculation which standard EN 15193 defines as the 'Constant illuminance factor (Fc)'. The constant illuminance factor 'Fc' is the ratio of the average input power over a given time to the initially installed input power to the luminaire.

Below are the Fc factors for the different building types:

Building Type

Constant illuminance factor (Fc)

Office (Small, Medium, and Large)










Apartment (Mid-Rise, High-Rise)




Here are some rule-of-thumb numbers for particular building use types. If you have multiple uses in the space use an area-weighted average to get the overall LPD.

Try to use LED lights to go lower than the below numbers and be sure to ask the lighting designer to lower their lighting as far as possible. These are very conservative assumptions.

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