Describe lumens-per-watt as a measure of lighting energy efficiency.

• A. Light output per bulb is the same regardless of watts.
• B. Lumens-per-watt is a measure of lighting energy efficiency; higher means more light per energy unit; drives energy savings.
• C. Lumens-per-watt measures heat generation.
• D. Luminous flux per square meter.

Answer: (B)

Lumens-per-watt shows how efficiently a lamp turns electrical power into visible light. Luminous flux (lumens) measures perceived brightness, while watts measure energy input. By dividing lumens by watts, you get the lumens-per-watt value, which indicates light output per unit of energy. A higher number means more light per watt, which translates to energy savings and lower operating costs over time. This metric is what you use to compare different lamp technologies and gauge improvements in efficiency. For context, incandescent bulbs are relatively low in lm/W, while modern LEDs and similar technologies deliver much higher lm/W. Keep in mind that lumens-per-watt doesn’t cover color quality, beam spread, or lifespan, and lux—the luminous flux per square meter—measures illuminance on a surface, not efficiency.