A rate is a ratio of unlike quantities, such as miles/ hour, beats/minute, and points/game. Efficacy is a special type of ratio that represents a rate of consumption, such as miles/gallon and gallons/flush, where one side of the fraction represents a benefit and the other a cost. With miles/gallon, the benefit is miles driven and the cost is gallons of fuel consumed. With gallons/flush, the benefit is the removal of waste by the flush and the cost is gallons of water consumed. Efficacy is intended to be a measure of the ability of something to do what it is supposed to do. Luminous efficacy is defined as a ratio of lumens per watt and is applied to light-emitting devices such as LED emitters, lamps, and luminaires. Implicit is that lumens are a suitable proxy for lighting’s benefit and watts are a suitable proxy for lighting’s cost. Uncomfortably, this is often not true when light-emitting devices are employed in lighting applications. Lumens may be good or bad. A “good lumen” is one that does what it is supposed to do. Good lumens enable a person to read a book, reinforce architectural form, create visual delight through desirable patterns of shade, shadow, and highlight, or evoke an alerting effect when alertness is desired. A “bad lumen” is one that does a poor job for its purpose or produces deleterious effects on vision or health. Most lumens generated never enter a person’s eyes; those lumens do not support any beneficial outcome and are waste. Sometimes unwelcomed lumens enter the eyes. This includes lumens that cause visual discomfort as with excessively bright luminaires, lumens that reduce task visibility through veiling reflections, lumens that distort colors due to poor spectral quality, and lumens that disrupt circadian rhythms due to inappropriate timing, intensity, spectrum, or duration of exposure. The benefits of light to people are as a stimulus for vision that enables visibility, perceptions of color, and psychological reinforcement, and as a stimulus for health-related effects that include alertness, entrainment of circadian rhythms, and sleep quality. We cannot expect a simple ratio to encapsulate all of these potential benefits, but we can question the veracity of lumens as a suitable proxy for any of them. Watts are an imperfect proxy for the cost of light for two primary reasons. First, watts are a measure of power, not energy. The cost of lighting in end-use applications, both in dollars and in carbon emissions, is time-dependent. Light-emitting devices that are frequently switched off consume little energy even if they have low luminous efficacy. Second, electrical power can be generated with different technologies. A watt from a coalfired power plant is environmentally costly, but a watt generated by a photovoltaic cell via conversion of sunlight is benign. As renewable energy production expands, the energy source is increasingly relevant to the calculus of lighting’s costs. Some things that reduce the luminous efficacy of light-emitting equipment may produce desirable benefits in application. Luminaire optical elements reduce luminous efficacy by absorbing or redirecting lumens that may otherwise cause visual discomfort. Higher quality color rendering is associated with lower efficacy. LEDs with lower CCT tend to have lower efficacy than those with higher CCT, but may better support user needs in some settings. In summary, luminous efficacy is a narrow performance measure for light-emitting devices, whereas a holistic evaluation of applied lighting requires a contextual assessment within the built environment. Total system performance depends not just on lamps and luminaires, but also upon how those products are installed and controlled, occupant outcomes, and the application environment—aspects that cannot be reduced to lumens or watts.

中文翻译：

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发光功效的问题

比率是不同数量的比率，例如英里/小时、节拍/分钟和积分/游戏。功效是一种特殊类型的比率，表示消耗率，例如英里/加仑和加仑/冲洗量，其中分数的一侧代表收益，另一侧代表成本。使用英里/加仑，收益是行驶里程，而成本是消耗的加仑燃料。使用加仑/冲洗，好处是通过冲洗去除废物，而成本是消耗的加仑水。功效旨在衡量某事做它应该做的事情的能力。光效定义为每瓦流明的比率，适用于发光器件，如 LED 发射器、灯和灯具。隐含的意思是流明是照明效益的合适代表，瓦特是照明成本的合适代表。不舒服，当在照明应用中使用发光器件时，情况往往并非如此。流明可能好也可能坏。一个“好的流明”是一个做它应该做的事情。良好的流明使人们能够阅读一本书，加强建筑形式，通过理想的阴影、阴影和高光模式创造视觉愉悦，或者在需要警觉时唤起警觉效果。“坏流明”是指在其目的上表现不佳或对视力或健康产生有害影响的流明。产生的大多数流明从未进入人的眼睛；这些流明不支持任何有益的结果并且是浪费。有时不受欢迎的流明会进入眼睛。这包括导致视觉不适的流明，如过亮的灯具，通过遮蔽反射降低任务可见度的流明，由于光谱质量差而使颜色失真的流明，以及由于时间、强度、光谱或暴露时间不当而扰乱昼夜节律的流明。光对人们的好处是作为视觉刺激，使能见度、颜色感知和心理强化，以及作为健康相关影响的刺激，包括警觉性、昼夜节律的夹带和睡眠质量。我们不能指望一个简单的比率来囊括所有这些潜在的好处，但我们可以质疑流明作为其中任何一个的合适代表的真实性。由于两个主要原因，瓦特不能完美地代表光的成本。首先，瓦特是功率的量度，而不是能量的量度。最终用途应用中的照明成本，无论是美元还是碳排放，都与时间有关。经常关闭的发光设备即使发光效率低，也消耗很少的能量。其次，电力可以通过不同的技术产生。来自燃煤发电厂的一瓦特对环境来说代价高昂，但光伏电池通过阳光转换产生的一瓦特则是良性的。随着可再生能源生产的扩大，能源与照明成本的计算越来越相关。一些降低发光设备发光效率的东西可能会在应用中产生理想的好处。灯具光学元件通过吸收或重新引导可能导致视觉不适的流明来降低发光效率。更高质量的显色性与更低的功效相关。具有较低 CCT 的 LED 往往比具有较高 CCT 的 LED 具有较低的功效，但在某些设置中可能更好地支持用户需求。总之，发光效率是发光设备的狭义性能衡量标准，而对应用照明的整体评估需要在建筑环境中进行上下文评估。整体系统性能不仅取决于灯具和灯具，还取决于这些产品的安装和控制方式、居住者的结果以及应用环境——这些方面都不能降低到流明或瓦特。