Final answer:
Lighting efficiency refers to the overall effectiveness of converting input energy into light, while luminous efficacy measures the amount of visible light produced for each Watt of power consumed. Advances in technology have improved luminous efficacy from primitive candles to modern LEDs. However, there's a theoretical limit to luminous efficacy around 300 lm/W, meaning improvements cannot continue indefinitely.
Step-by-step explanation:
When we discuss the efficiency and efficacy of lighting, we are talking about how well a light source converts electrical energy into visible light. Efficiency refers to the overall effectiveness of a light source in converting input energy into output work, in this case, the production of light. In technical terms, it is the amount of useful energy or work provided by the light source divided by the total input of energy.
Efficacy, on the other hand, is a measure specifically known as luminous efficacy, which is expressed in lumens per watt (lm/W). This parameter measures how many lumens of visible light are produced for each watts of electrical power consumed. In essence, efficacy is about the light output about power input, while efficiency encompasses a broader perspective of energy conversion and utility.
To understand these concepts historically, we can look at traditional incandescent bulbs, which were rated by their power usage in Watts, not by the light they output. We now recognize that to compare brightness effectively, we should use lumens. As table 2.1 and figure 2.3 in referenced materials suggest, over time, advances in technology have significantly improved the luminous efficacy of light sources, from primitive candles to modern LEDs.
For example, a historical candle might have a luminous efficacy of 0.3 lm/W, while a modern LED can achieve around 100 lm/W--a substantial improvement. Yet, even with these improvements, we cannot continue this trend indefinitely. There is a theoretical limit to these numbers, which is approximately 300 lm/W for white light, meaning that at some point, we won't be able to improve the efficacy of lighting any further. This understanding of lighting efficiency and efficacy can help consumers make more informed choices about the lighting they use, aiming to reduce power consumption and environmental impact.