Lumens measure the actual brightness of a light source, with higher lumens indicating a brighter light. Watts, conversely, measure energy consumption. Historically, higher wattage meant brighter light, but with energy-efficient options like LEDs, watts no longer accurately reflect brightness. For example, an LED bulb can produce the same brightness (lumens) as an older incandescent bulb while consuming significantly fewer watts. Understanding lumens is crucial for selecting appropriate lighting for different spaces and reducing electricity costs.