How is light source efficiency measured?

Light source efficiency is measured in lumens per watt. This measurement indicates how effectively a light source converts electrical power (watts) into visible light (lumens). The higher the lumens per watt value, the more efficient the light source is at producing light for each unit of energy consumed. This ratio is crucial for comparing the efficiency of different lighting technologies, allowing for the selection of lighting solutions that provide the desired illumination while minimizing energy consumption.

Other options listed do not represent measures of efficiency in the same way. Lumens provide a measure of total light output but do not account for the energy used. Lumens per candela relates to intensity and distribution rather than overall efficiency, and candelas per degree pertains to directional intensity, which is not a direct measure of how efficiently a light source utilizes energy.