A 30 ft × 20 ft office space has a photosensor dimmer control working with installed lighting of 2 W/ft2. The required workplace illuminance is 60 fc and the available daylighting is calculated as 40 fc on the summer peak afternoon. Determine the payback period for the dimmer control system assuming the following: 1-1/2 ton cooling installed for 600 ft2 at $2200/ton, lighting control system cost at $1/ft2, 30% reduction in annual lighting due to daylighting, $0.10/kW h electricity cost, and cooling for 6 months at a COPc = 2.5.