Smart Lighting Savings Calculator

This model compares the connected load of an incumbent outdoor lighting population against an LED population operating under controls. The physical driver is luminous efficacy: high-pressure sodium cobrahead luminaires deliver roughly 60 to 110 lumens per watt at the fixture once poor optical control is accounted for, metal halide typically 50 to 90 lumens per watt with heavy lumen depreciation, while current outdoor LED luminaires reach 130 to 180 lumens per watt with directional optics that put light on the roadway rather than into the sky. That is why a 250 W HPS fixture is usually replaced by an 80 to 120 W LED at equal or better illuminance. Annual energy is fixtures times watts times annual burn hours divided by 1000; dusk-to-dawn operation averages about 4,100 to 4,400 hours per year at mid latitudes. The dimming and occupancy percentages apply only to the LED base load, and this model subtracts them additively, so entering values that sum above roughly 60 percent overstates savings because the two controls act on overlapping hours. Adaptive dimming in practice means dropping one lighting class overnight under IES RP-8 or CIE 115, commonly 30 to 50 percent output between midnight and 5 a.m. The 0.42 kg CO2 per kWh grid factor is a mid-range value; coal-heavy grids exceed 0.7 and hydro-dominated grids fall below 0.05, so emissions results should be re-based on local data. The maintenance term assumes LED upkeep at 30 percent of incumbent cost, and payback here is simple payback with no discount rate, rebates, or installation labor included.

Electric street lighting began with Charles Brush arc lamps installed in Cleveland, Ohio in 1879, followed by incandescent and then mercury vapor lamps in the 1930s and 1940s. High-pressure sodium, commercialized by General Electric in the mid-1960s, displaced mercury vapor across most of the developed world during the 1970s and 1980s because its efficacy was roughly double, and its characteristic orange light defined the night-time appearance of cities for a generation. The efficiency ceiling of gas-discharge technology, however, was essentially reached by the 1990s. The change came from semiconductors. Shuji Nakamura, working at Nichia Corporation in Japan, produced a high-brightness blue indium gallium nitride LED in 1993, and phosphor-converted white LEDs followed in 1996; Nakamura shared the 2014 Nobel Prize in Physics with Isamu Akasaki and Hiroshi Amano for that work. Outdoor LED trials began in the mid-2000s, and the US Department of Energy accelerated adoption through its GATEWAY demonstrations and the Municipal Solid-State Street Lighting Consortium formed in 2010. Los Angeles started a retrofit of roughly 140,000 streetlights in 2009 and completed the bulk of it by 2013. Controls became practical once ANSI C136.41 standardized the seven-pin dimming receptacle, letting cities add sensors and network nodes to existing sockets, while the TALQ Consortium, founded in 2012, worked on management-software interoperability across vendors.