Use the following formula to calculate your dollar savings from an occupancy-sensing lighting control system:
A. Power Reduction in Unoccupied Periods This number ranges from 0.50 to 0.84 and depends on fixture type and control strategy. HID lamps cannot be turned completely off owing to warm-up limitations. EIA standards and lamp warranties limit the reduction of HID fixture wattage to 50% during dimmed operation.
Fluorscent lamps have no warm-up limitations. The effective reduction in wattage for line-voltage switched fluorescent fixtures can be as high as 84% while maintaining “night-lighting” in aisles. This figure corresponds to triple-ballasted fixtures that “idle” to a single powered ballast interleaved 1:1 with fixtures that idle to full dark.
B. Fixture Load in Kilowatts Choose a fixture type and wattage from this table:
Fixture Size & Type
Load in kW
6 lamp F54T5HO
6 lamp F32T8
C. Annual Operating Hours in Idle Mode Estimate the number of hours per day that your fixtures operate in idle mode multiplied by the number of workdays per year. (Viewpoint offers a motion-sensing traffic meter that helps you measure this.)
Half-Day Loading Dock Example:
12 hour workday on weekdays only with dimmed lighting 80% of the time. 12 hours per day x 0.8 idle x 260 days per year= 2500 hours per year in idle mode.
Full-time Distribution Center Example:
24/7 workday with dimmed lighting 75% of the time. 24 hours per day x 0.75 idle x 365 days per year= 6570 hours per year in idle mode.
D. Total Controlled Fixtures This is the number of fixtures in your facility that will be equipped with motion sensing.
E. Cost Per Kilowatt Hour This number is expressed as a fraction of one dollar and ranges from $ .06 to $ .14 for most areas.
Example: Full-time distribution center with qty=500 HID fixtures rated 400 watts and local electricity costs at 10 cents/kWh: