Think of lumens as a new way of knowing how bright a lamp is. Lumens = Light Output. In simple terms, Lumens (denoted by lm) are a measure of the total amount of visible light (to the human eye) from a lamp or light source. The higher the lumen rating the “brighter” the lamp will appear. We have all bought 50W or 60W conventional bulbs or spotlights in the past expecting a certain level of brightness.