Lumens is actual total visible light output whereas Watts is power consumed by the bulb, which is only indirectly related to light output depending on the bulb's efficiency. An ordinary incandescent lamp is quite inefficient and puts out a lot of its light in non-visible infrared light. A quartz halogen lamp moves much of the infrared into the visible so puts out more light for a given Wattage. LEDs are much better yet.