Lighting Energy Consumption

Home Energy Saver

Accurately estimating the energy consumption of lighting requires detailed information about the technical specification of the fixture and the typical usage pattern for that fixture. Since not all consumers are willing or able to provide that level of detail, the Home Energy Saver offers a means to arrive at lighting consumption with minimal user input as well as a more complete calculation model.

Lighting fixtures are grouped according to the room in which they are located. Equation 31 calculates the lighting energy consumption for all fixtures in a room. Lighting default lamp counts, wattages, and hours of use by room are listed here.

Lighting consumption at the household level is simply the sum of energy consumed by all rooms as shown in equation 1.

            Equation 1


            EC = Annual lighting energy consumption by room (kWh/year)

            FE = Fixture energy (kWh/year)

            n = number of fixtures in room

The fixture energy represents the energy consumption of both the lamp and ballast components of a light fixture. A fixture consists of all the lamps controlled on a single circuit. Fixture energy is calculated using Equation 2.

           Equation 2



Plamp = combined power for all lamps in fixture (Watts)

Pballast = total ballast power for fluorescent fixtures (Watts)

usage = fixture usage (hours/day)

365 is days per year

Note that ballast energy is only applicable for fluorescent tube fixtures. Any ballast energy for compact fluorescent fixtures and halogen fixtures is included in the total lamp wattage for the fixture, entered by the user. Ballast fixture power is given by equation 3.

                       Equation 3


130 = Ballast power (Watts)

NL = number of lamps in fixture

[Note (NL/2) is rounded to next-higher integer value]


Scoring Tool

Consistent with its asset rating model of the Scoring Tool has no user inputs to the lighting energy estimation, rather lighting energy is estimated based on typical energy intensity and the building floor area. The energy intensity estimates are from Hendron and Engebrecht (2010). The calculation of lighting energy in the Scoring Tool is described in equations 4 and 5.

LUsein  = 455 + 0.8 * conditioned floor area            Equation 4

LUseout= 50 + 0.05 * conditioned floor area            Equation 5


LUsein = Interior lighting electricity use (kWh/year)

LUseout = Exterior lighting electricity use (kWh/year)

CFA = Conditioned floor area