Lighting-only energy savings is essentially the money you save from the simple wattage reduction when switching to more efficient lighting products. A “lighting-only” number is a good place to start because it is the most conservative savings calculation in a lighting retrofit and it represents the bulk of the savings you will capture on most retrofit projects. Further, it is to be trusted. It’s plain science and math.

  • Step 1: Gather your facts

You will need to pull together the following items before we dive into the calculations

  1. Old lighting product wattage: In our example, this is 400 watts.
  2. New lighting product wattage: In our example, this is 150 watts.
  3. Running time: How much time out of the day is the product lit?
  4. BC Hydro Electricity rate at this time is $0.1073 per kWh.


  • Step 2: Calculate energy savings per lighting fixture

Old Product Wattage – New Product Wattage

= Energy Savings per Lighting Fixture

Our Example:

400 Watts (Old Metal Halide) – 150 Watts (New LED)

= 250 Watts Saved per Lighting Fixture

  • Step 3: Calculate annual running time

The amount of time that a product is lit has a significant impact of savings and payback.

In our example, we assumed the lighting is on 12 hours per day and 365 days per year.

Daily Run Time x Annual Days of Operation

= Total Annual Run Time

Our Example:

12 Hours per Day x 365 Days per Year

= 4,380 Hours

  • Step 4: Calculate total annual energy savings

BC Hydro charges $0.1037 for electricity by the “Kilo Watt Hour”

  • 1000 Watts = 1 kW
  • kW’s of Lighting = Number of Lighting Fixtures x Total Wattage of each fixture
  • kWh’s = Total kW’s x hours of use (Per Day/Week/Month/Year)

Energy Savings per Lighting Fixture x Total Annual Run Time ÷ 1,000

= Total Energy Savings

Our Example:

250 Watts Saved per Lighting Fixture x 4,380 Hours per Year ÷ 1,000

=1095 kWh Saved

  • Step 5: Calculate annual dollar savings

Okay, so we know we’re saving a boatload of electricity, but we need to see how it translates to real dollars.

Total Energy (kWh) Savings x Electricity Rate

= Total Dollar Savings (from Lighting Only)

Our Example (Watts Commonly Found In Warehouses & Parking Lots):

1095 kWh Saved x $0.1037 per kWh

= $113.55 Saved Per Lighting Fixture Per Year

  • $1135.52 Saved Per 10 Lighting Fixtures Per Year
  • $5,677.58 Saved Per 50 Lighting Fixtures Per Year
  • $11355.15 Saved Per 100 Lighting Fixtures Per Year

Now that you’re a pro on figuring out how much you can save per lighting fixture, you can scale to any size product and get a “gut-check” on the savings estimates that find their way to your desk.