What does high efficacy in a lighting system indicate?

High efficacy in a lighting system indicates high light output per watt of electricity consumed. This means that the system is efficient in converting electrical energy into light, providing more illumination for each unit of energy used. Higher efficacy is desirable because it not only leads to lower energy bills but also demonstrates a reduced environmental impact due to less electricity consumption.

In contrast, options such as high energy consumption are indicative of inefficiency in a lighting system, where more electricity leads to less effective lighting output. Long lifespan of the fixture pertains to durability, affecting maintenance schedules and replacement costs, but does not directly relate to efficacy. Similarly, low installation cost relates to the initial expenditure rather than the efficiency of light output in relation to energy usage. Focusing on light output per watt is essential for assessing the operational efficiency of lighting systems, making the chosen answer the most accurate.