Lumens and wattage
Back in the day, the wattage of a lightbulb determined how much light it would emit, with a 80W bulb being twice as bright as a 40W bulb.
However, light bulbs have gotten much more efficient over time, with new technologies emerging all the time. Because of this, the term lumen now refers to how bright a bulb is, while the wattage is how much power it is using. As an example, a 4W LED bulb, while only using a small amount of power, can throw out 400 lumens, about as much as an old style 40W bulb.
Since LED technology is always evolving, you always want to check the lumen count of a light before buying, as older style LED downlights might be using more power compared to current generation downlights while not throwing out as much light.