Holiday Light Calculator

LED bulbs draw roughly seven times less power per bulb than incandescent ones in this calculator's model, and that wattage difference doesn't just lower the electricity cost — it directly reduces total amp draw, which in turn reduces how many circuits the display needs and how many light strings can safely share a single 15-amp circuit. A display that requires multiple dedicated circuits in incandescent bulbs might comfortably run on just one circuit in LED.

This reflects the standard electrical safety practice of not loading a circuit past 80% of its rated capacity for anything running continuously for an extended period, which holiday lights typically do for hours each evening — running a circuit at its full rating for that long risks nuisance breaker trips or excess heat buildup in the wiring. This 80% guideline is a widely followed safety margin, not a Calcimator-specific assumption.

Yes, and proportionally so — daily electricity cost scales directly with hours run per day, so cutting run time from, say, 8 hours down to 4 cuts the electricity cost in half for an identical light display, with zero change to the strings, bulbs, or wattage involved. A timer that automatically shuts lights off late at night, once most passersby have gone home, is one of the simplest ways to meaningfully reduce the season's total cost.

Circuits needed tells you the minimum number of separate 15-amp circuits required to safely power your entire planned display without exceeding the safe load on any one circuit, while max strings per circuit tells you, for the specific bulb type and string size you entered, how many individual strings could be safely daisy-chained onto just one circuit before hitting that same safe load limit. Comparing the two together helps you figure out how to physically distribute your strings across the outlets and circuits actually available at your house.