A watt (W) is a unit of power equal to one joule per second. In fixture specifications, wattage usually describes electrical input power or an emitter rating; check which value the manufacturer is reporting.
Wattage and light output
Electrical input is not a photometric measurement. Different sources and optics can turn the same electrical power into different amounts and distributions of visible light. Use lux at the required distance and coverage when comparing how a fixture will light a scene.
Reading the right number
A product name or nominal LED wattage may differ from the complete system’s maximum input. Power supplies, control electronics and operating modes can affect consumption. Use the manufacturer’s rated input and current information for the complete system when planning power.
Practical example
Two lights labelled “300 W” can have different centre lux, colour output and maximum electrical draw. Compare the relevant specifications separately. A watt figure alone is not enough to approve a circuit load, battery configuration or cable arrangement; those decisions also depend on the equipment ratings and supply conditions.
Related terms
Lux · Lumen · PWM (Pulse-Width Modulation) · Voltage · Amperage · Power Factor · Apparent Power · Inrush Current