What’s the difference between efficiency and efficacy?
Efficacy is a term normally used in cases where the input and output units differ. In lighting, we are concerned with the amount of light (in lumens) produced by a certain amount of electricity (in watts). On the other hand, efficiency is a term that is typically dimensionless. For example, lighting fixture efficiency is the ratio of the total lumens exiting the fixture to the total lumens initially produced by the light source. top How do you evaluate LED products? Lumen output is only part of the story and can be misleading. To fully evaluate an LED product one needs to review the overall system efficiency, optical control, thermal management of the LEDs, and know at what point in time the fixture will reach 30 percent lumen depreciation. Products with good optical efficiency and thermal management will be able to deliver more lumens, on average, than traditional HID products. As the US Department of Energy concluded in its Solid-State Lighting (SSL) Commercial Product Testing Progra
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