Which statement best describes the relationship between lumens and watts?

Which statement best describes the relationship between lumens and watts?

• A. Lumens measure energy consumption; watts measure light output
• B. Lumens and watts measure the same thing
• C. Lumens measure electrical current; watts measure voltage
• D. Lumens measure light output; watts measure energy consumption

Answer: (D)

Lumens describe how much visible light a source emits, i.e., its brightness. Watts describe how much electrical power the light uses, i.e., energy consumption. That distinction is why the best statement is that lumens measure light output while watts measure energy consumption. Because of efficiency differences, you can have a low-wattage bulb that shines as bright or brighter than a higher-wattage one, thanks to more lumens per watt. The ratio of lumens to watts (lumens per watt) is a handy way to compare efficiency. The other ideas mix up what each unit measures or claim they measure the same thing, which isn’t correct.

Lumens describe how much visible light a source emits, i.e., its brightness. Watts describe how much electrical power the light uses, i.e., energy consumption. That distinction is why the best statement is that lumens measure light output while watts measure energy consumption. Because of efficiency differences, you can have a low-wattage bulb that shines as bright or brighter than a higher-wattage one, thanks to more lumens per watt. The ratio of lumens to watts (lumens per watt) is a handy way to compare efficiency. The other ideas mix up what each unit measures or claim they measure the same thing, which isn’t correct.