Metal halide fixtures provide indoor and outdoor illumination in many places that require wide overhead lighting such as athletic facilities, parking lots, warehouses and factories. Metal halide bulbs are valued for their high luminous efficacy (75-100 lumens/watt) and intense white light.
The upfront costs of these fixtures may be low but when maintenance and electricity costs are taken into account, the overall cost is rather high. Let’s look at the math behind calculating the operating costs.
Determine the number of actual watts used by one of your fixtures. Use the fixture wattage + wattage used by the associated ballast. Typical wattages are shown below.
- 175 watt fixture = 205 actual watts
- 250 watt fixture = 290 actual watts
- 400 watt fixture = 458 actual watts
- 1000 watt fixture = 1081 actual watts
Multiply the watts that your fixture uses by the total number of fixtures that you have to determine total watts. (single fixture watts) x (number of fixtures) = TOTAL WATTS
Example: (290 watts) x (30 fixtures) = 8700 total watts
Divide total watts (from step 2) by 1000 to determine total kilowatts. TOTAL WATTS/1000 = TOTAL KILOWATTS
Example: 8700 total watts / 1000 = 8.7 total kilowatts
Determine how many hours your lights are on per year. This doesn’t need to be exact, just a rough estimate. Start by determining how long they are on per day and then multiply number of days per year. For our example, we will use 3,000 hours per year.
Calculate kilowatt hours, which are typically used for billing units for energy delivered by electric utilities. (total kilowatts) x (hours per year) = KILOWATT HOURS
Example: 8.7 x 3,000 = 26,100 kilowatt hours
Determine the amount charged by your electric utility per kilowatt hour and calculate annual energy cost. (price per kilowatt hour) x (kilowatt hours) = ANNUAL ENERGY COST
Example: $0.09 x 26,100 = $2,349.00
Calculate how much it costs per year for each light fixture that you have. (annual energy cost) / (number of fixtures) = ANNUAL ENERGY COST PER FIXTURE
Example: $2,349.00 / 30 = $78.30
The final calculations for annual energy costs are then added to the initial cost of the light fixtures and their associated bulbs. One of the main issues with metal halide bulbs is that they tend to lose 50% of their light output half way through their typical lifespan. This is not the case for high pressure sodium, LED and induction alternatives. These alternatives also have longer average lifespans. They may have higher upfront costs (especially LEDs), but energy savings and lower maintenance costs realized over a period of time will offset this. Take some time to look at our lighting selection at Warehouse-Lighting.com or call to speak to one of our lighting experts about your lighting needs.