These inputs allow the user to describe the lighting load in TREAT.


This input allows the user to assign a unique name to the lighting fixture or the group of lighting fixtures.

Watts per Fixture:

Used to enter Watts per fixture including ballast (if any).

Hours on Per Day:

This input allows the user to enter average daily usage time for the fixture(s). The input in this field is used to generate the hourly schedule depending on the type of space in which the lighting is located. The hourly schedule for each type of space is as follows:

  1. Sleeping Quarters: center hours on 10 pm;
  2. Living Space: center hours on 8 pm;
  3. Office: center hours on 1 pm;
  4. Outdoor lighting : center hours on 10 pm;
  5. All other spaces: center half the usage on 7 am and the other half on 7 pm.
Note: According to a pilot study “Incorporating Lighting and Appliance Energy Consumption into the Home Energy Rating Score” prepared by Architectural Energy Corporation, the statistical average connected lighting load in single family houses is 1.25 W/sqft and the lamps are lit on average 2.34 hours/day.

A monitoring project commissioned by the Bonneville Power Administration and Tacoma Public Utilities referenced on LBL website (, Tribwell and Lerman, 1996) showed similar results, with an average of 2 hours per day operating time and lighting load of 1.47 W/sqft.

When the exact lighting usage in an existing home is not known, the statistical averages presented above should be used to enter the lighting load in TREAT.

Note: Lighting load distribution throughout the day may significantly affect heating and especially cooling load. Compare two cases – in one case a single 60W bulb is lit 24 hours/day; in the other case eight 60W bulbs are lit 3 hours during night/evening time. In both cases the lighting load is 1440Wh/day, but cooling usage on a mild summer day when cooling is needed during the day but not at night may differ significantly. In the first case the lighting increases cooling load; in the second case cooling and lighting do not interact with each other since they do not occur simultaneously.


Enter the total number of fixtures in the group.


Select the space where the group of fixtures is located or exterior. Exterior fixtures contribute to the base load calculations but not to the space internal gains.

Copy Lighting from Another Space: 

This button found above the Feedback Panel opens the Lighting Wizard window. The Lighting Wizardallows the user to copy lighting from one space to the other spaces. It should be used if spaces in the project have similar lighting.

  • Copy All Lighting From select the space from which you would like to copy lighting.

To specify the spaces to which the lighting will be copied.

  • Every Conditioned Space: radio button indicates that the lighting will be copied to each space that was specified as conditioned on Spaces screen.
  • Every Unconditioned Space: radio button indicates that the lighting will be copied to each space that was specified as unconditioned on Spaces screen.
  • Let Me Pick the Spaces: radio button allows user to select spaces to which the lighting will be copied.
  • Add to already defined lighting in theses spaces: radio button indicates that the new lighting will be added to the lighting that may have been already specified for these spaces.
  • Replace already defined lighting: radio button indicates that the new lighting will replace any lighting that has been entered for these spaces.

Input on this screen affects not only base load calculations, but also calculation of heating and cooling energy consumption due to interaction between cooling and internal gains. You may enter a single record per conditioned space to model overall building base load. TREAT assumes that 100% of lighting energy is lost in the form of heat to the space where the lighting is located.