Luminous efficacy is a measure of how well a light bulb emits visible light at a given power. It is the ratio of luminous flux to power, measured in lumens per watt(lm/W). Higher luminous efficacy means the light bulb is more energy efficient as more light is produced using less power. With luminous efficacy or lumens per watt, we can convert lumens to watts or watts to lumens and compare bulbs of different types.