Daylighting Tool

Daylighting is the practice of replacing opaque walls or roof materials with light transmitting panels to allow natural light into the facility to provide effective internal lighting. By using light transmitting panels for roof panels, significant energy savings can be achieved from the reduced use of artificial (electric) lighting. Artificial lighting energy use can be reduced by simply installing fewer electric lights because daylight is present, or by dimming or switching electric lights automatically in response to the presence of daylight, a process known as daylight harvesting.

This calculator was developed to provide a very general estimation of potential energy savings and simple payback. Any final economic decisions should be based upon the use of more extensive analytical tools.


For the Daylighting Tool, users will need to input the following:

  • Length and width of installation area
  • Current lighting specifications including number of fixtures, input Watts per fixture, lumens/fixture, annual operating hours, and incremental energy cost
  • Panel specifications such as minimum illuminance through a light transmitting panel for the user's location, and the light transmission of the panels selected

Based on input, the Daylighting tool will estimate the current energy consumption, potential energy savings, and potential cost savings. In addition, the tool will provide a comparison of the current versus proposed lumens per square foot.

Downloadable Version of the Daylighting Tool

This version of the tool can be downloaded and installed on a local computer to run the tool. System requirements to use the tool include:

  • Microsoft Excel 2003 or newer

Download the offline version of the Daylighting Tool

Additional Resources

This tool is based on a similar tool created by the Oregon State University Efficiency Center. More information about the Oregon State University Efficiency Center can be found on the OSU Energy Efficiency Reference (EEREF) website at Similar tools to the Daylighting Tool can be found on the OSU Opportunity Templates website at