Light Pollution Calculator Formula

Understand the math behind the light pollution calculator. Each variable explained with a worked example.

Use the Light Pollution Calculator

Formulas Used

Wasted Lumens

wasted_light = wasted_lumens

Wasted Energy per Year

wasted_energy = wasted_kwh

Annual Wasted Cost

wasted_cost = wasted_kwh * elec_rate

Total Annual Lighting Cost

total_energy_cost = annual_kwh * elec_rate

Variables

VariableDescriptionDefault
num_fixturesNumber of Light Fixtures10
lumens_per_fixtureLumens per Fixture(lumens)4000
uplight_pctUpward Light Percentage(%)30
watts_per_fixtureWatts per Fixture(watts)50
hours_per_nightHours On per Night(hours)10
elec_rateElectricity Rate(USD/kWh)0.15
wasted_lumensDerived value= num_fixtures * lumens_per_fixture * uplight_pct / 100calculated
annual_kwhDerived value= num_fixtures * watts_per_fixture * hours_per_night * 365 / 1000calculated
wasted_kwhDerived value= annual_kwh * uplight_pct / 100calculated

How It Works

How to Calculate Light Pollution

Light pollution is wasted light that shines upward or sideways instead of illuminating the intended area.

Formula

Wasted Lumens = Fixtures * Lumens * Uplight %

Wasted Energy = Total Energy * Uplight %

Types of Light Pollution

  • Skyglow: Brightening of the night sky over populated areas
  • Glare: Excessive brightness causing visual discomfort
  • Light trespass: Light falling where not needed
  • Clutter: Excessive groupings of light sources

    • Fully shielded fixtures eliminate uplight and reduce waste by 30-60%.

    Worked Example

    10 fixtures at 4,000 lumens each, 30% uplight, 50W each, running 10 hours/night at $0.15/kWh.

    num_fixtures = 10lumens_per_fixture = 4000uplight_pct = 30watts_per_fixture = 50hours_per_night = 10elec_rate = 0.15
    1. 01Wasted lumens: 10 * 4,000 * 30% = 12,000 lumens
    2. 02Annual energy: 10 * 50 * 10 * 365 / 1,000 = 1,825 kWh
    3. 03Wasted energy: 1,825 * 30% = 548 kWh
    4. 04Wasted cost: 548 * $0.15 = $82/year

    Ready to run the numbers?

    Open Light Pollution Calculator