Luminous efficacy: efficiency of the light source in lm/W
Luminous efficacy is defined as the ratio of emitted luminous flux Φ (measured in lumens lm) to expended electrical power of a light source (measured in watts W). Specified in lumens per watt (lm/W), luminous efficacy is thus a measure for evaluating the efficiency of lamps such as LEDs, or also the luminaire itself including control gear and optic.
Formula for calculating luminous efficacy.
The efficiency of luminaires is often used as a criterion for sustainability. At least 100lm/W is an important value here. However, especially with accent lighting, the effectiveness, i.e. the lux per watt value (lx/W), is more relevant. This is because when illuminating a room, it is important to check where exactly light is needed in order to reduce it everywhere else. This way, light only reaches the relevant target areas. Energy consumption is thus reduced.
