LED manufacturers utilize industry-accepted parameters such as Color Rendering Index (CRI) and Correlated Color Temperature (CCT) to characterize the light emitted by their products. CRI considers light quality and CCT to be measures of source temperature. These measures allow lighting engineers to choose light engines that appeal to consumers for efficient, long-lasting lighting in place of inefficient incandescent bulbs.
However, new research claims that it is not enough to use CRI and CCT alone, and that real LEDs are used for the characteristics of solid-state lighting (SSL). In its place is a concept known as "Color Class A," which combines CRI with CCT and Gamut Area Index, and is considered a better choice. The study concluded that 75% of consumers believe that Class A color light sources provide the best color rendering and the best saturation levels.
This article explains what it is and how it complements CRI and CCT to emphasize the concept of class A color. The article goes on to explore how leading manufacturers are incorporating Class A colors into their latest products.
Characterize LEDs
Home or office lighting is provided by traditional light sources such as incandescent, fluorescent or halogen or more modern SSL with little difference and consumers have strong perceptions of the "quality" of lighting. Their views vary by location: in offices, for example, workers are more receptive to relatively harsh "blue" light, which makes it easier to read documents and work in front of computer screens, but at home, Soft, warm lighting is often preferred because it aids relaxation.
Engineers have worked hard to translate consumers' qualitative assessments of light into quantitative ones, so that different light sources can be described and directly compared. Two common measures of light quality are CRI and CCT.
CRI is a measure of the ability of a light source to faithfully reproduce the color of various objects compared to ideal or natural light sources. The index is formed by the Commission Internationale de l'éclairage (CIE, or "International Commission on Illumination in English").
The test uses eight or more CIE standard color samples and measures different chromaticities when viewed under a reference source under test lamps (Figure 1). The larger the difference, the higher the CRI. (See the District article "What is Color Rendering Index and Why Does It Matter?".)
CRI test images of eight standard color samples
Figure 1: The CRI test uses eight standard color samples to measure the difference in chromaticity, with the test lamp under the reference source.
As the technology matures and the index of LED devices exceeds 70, the CRI of LEDs has improved. For example, Philips Lumileds' Luxeon T, 111 lm/W (2.8 V, 700 mA) LED has a minimum CRI of 80 for a CCT range of 2700 to 5000 K.
The definition of CCT is "the sensory color of a Planck radiator that is closest to the temperature of a given stimulus at the same brightness under specified viewing conditions." In fact, LED manufacturers produce CCTs or close, equivalent to incandescent lamps A "black body" will appear as the Planck locus product ("color space") of the 1931 Planck locus of color in the CIE xy chromaticity diagram of changes in radiation and temperature.
The output of white LEDs produced by manufacturers is divided into "warm white" (2600 to 3700 K CCT), "neutral white" (3700 to 5000 K CCT) and "cool white" (5000 to 8300 K CCT).
The chromaticity of the light emitted from the LEDs on the locus is classified as "white", but since the locus traces a line in the CIE color space, the chromaticity of the LED varies at various points on the line. For example, high CCT LEDs contain more blue wavelengths and therefore appear a blue one. Low CCT devices appear slightly red.
(Note: "warmer" white LEDs have a lower CCT. The output from these devices contains more red light that will radiate to the cooler end of the Planck locus even though human perception dictates that the color is warm. "Cool" white glows Diodes are bluer, and radiation is divided into heat, although again, humans have an alternative perception that determines the color characteristics of light cool [see Hi-Tech Section "Defining White LEDs"].)
A characterization system based on CRI and CCT has well established its reputation among consumers for the SSL industry. However, new research argues that in order to gain greater market share, the industry must up its game to satisfy increasingly discerning buyers. This argument follows that CRI and CCT do only partial characterization work, requiring additional light quality metrics.
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1947荷兰科学家命名为首次描述P. J. Bouma的特点，导致光源显色性好。总的来说，布马指出，具有良好的显色性光源，光或电，应揭示全方位的颜色(色相、明度、饱和度)，应使相似的光谱反射物体之间有良好的辨色能力(例如，紫色从栗色)，而不应扭曲颜色(例如，在光源不应过度提升肉在屠夫的展柜发红)。布马的定义表明，色不能由任何单一的指标来衡量，而结合几个。
在照明研究中心(LRC)在伦斯勒理工学院的研究人员发现，CRI和CCT用于描述光源的物理特性，但所缺少的是一个衡量“光是如何被人眼感知。”
LRC进行实验在他们要求观察员参加Farnsworth–孟塞尔100色相测试。测试措施隔离安排在常值和色度不同的颜色目标的细微差异的能力(色纯度)，覆盖所有的视觉色彩的孟塞尔颜色系统描述(孟塞尔系统是一个色彩空间指定基于三色尺寸：色调、颜色值(亮度)、色度)。
观察员提出了一个图片拼贴，依次照亮两种不同的光谱功率分布(SPD)。在切换到第二个SPD之前，观察者被允许在第一个SPD上观察他们的拼贴。一旦出现第二个SPD，在第一个SPD下就不能再看拼贴了。
对于每一个SPD配对比较，观察者首先被问到哪一个SPD使拼贴更全面，更生动。然后他们被问到哪一个SPD使拼贴画中的红色更生动，最后他们被问到哪一个SPD使布鲁斯更生动。同样，在第二届会议上，同样的光线水平，观察者被要求选择光源，他们认为拼贴更适合“自然”，其次是他们对红色的想法，然后是或多或少的自然的布鲁斯音乐。
这项研究得出结论，色域区域，或更确切地说，是一个有益的补充CRI和CCT，以确保良好的色彩歧视和令人满意的物体颜色“生动”和“自然”的看法。盖测量光源所呈现的色域，并可以通过在二维颜色空间中连接用于计算CRI的颜色点形成的有界区域来确定(图2)。一般来说，色域区域越大，颜色样本越饱和，就越容易区分它们。
光源色域面积指数图像
图2：光源的色域面积指数是由连接在二维空间中形成的有界区域计算出来的，用于计算CRI的颜色点。
定义类颜色
LRC得出光源提供最低CRI 80和80和100之间的一个盖将提供良好的颜色歧视，使场景中的对象显得生动自然提供足够的照明提供给视觉场景。换句话说，消费者更喜欢一种光源，它能增强色彩而不失真，或者使物体看起来不自然。
有趣的是，这项研究还揭示了芯片生产商在黑色轨迹上生产发光二极管的野心可能需要修改。在试验参与者被显示在六篇从2700到6500 K，在每一个CCT，测试者被要求在七个不同的色度值沿与值范围的上方和下方的黑色轨迹垂直CCT线判断质量轻。
只有在4100 K左右，参与者才能感知到高质量的白光与黑体轨迹相一致。在“冷”(高)的持续关连交易，参与者优选色度略高于轨迹;在“回暖”(下)CCT测试者色度明显低于位点(图3)。在2700 K时，例如，在黑体轨迹和“首选”的白光，相当于一13-15-step麦克亚当椭圆之间的感知差异。
类颜色的观察者偏爱图像
图3：在高CCT观察家喜欢白色点上面的黑色轨迹，4100 K以下，色度低于轨迹更受欢迎。
LRC使用结果从成白光质量接近盖和感知研究黑体轨迹来定义“阶级色彩”。为了满足A类颜色的定义，光源必须有80以上的CRI和80到100的范围。此外，低于4000 K CCT的源应该低于CIE XY 1931色空间的黑体轨迹，以匹配研究表明消费者在这些温度下的白光偏好的结果。
LRC表明高垓和CRI光源一直被认为是高质量的消费者比光源高只有这两个指标率。该组织还发现，该加第三度量CRI和CCT增强光质量的定量测量。¹²
架子上现在有一种颜色。
该行业还没有普遍接受的类颜色作为标准定义但这并没有阻止一些创业企业利用LRC的发现改变LED的规格。
普瑞，例如，最近推出了其韦罗éCOR系列A级板上芯片(COB)LED和声称是使用类的一个颜色指示第一公司(图4)。
普瑞光电Vero D的éCOR系列一级棒图像
图4：普瑞说，韦罗éCOR系列一级棒是上课一个颜色指示第一。
韦罗DéCOR系列一级棒可以在140流明/瓦产生1305流明(26.7 V、350 mA)，可在4000和3000 K CCT与CRIs为97和盖斯大于80。该公司表示，这些产品是专为高端零售、酒店、博物馆和商业空间等应用而设计的。
而不是促进其产品“类的颜色，”Cree还推出了一系列产品与CRI和盖的组合，满足一个类的定义。XRE系列具有111流明在96流明/瓦设备(3.3 V、350 mA)和4000 K产品拥有一台84和盖82。
今年早些时候，飞利浦Lumileds公司宣布crispwhite COB LED家庭。该产品提供3750流明的90流明/ W(35.5 V，1.2 A)和CRI为90。该公司已停止使用类彩色指示器或甚至提供的芯片一改评级。然而，飞利浦Lumileds是推动产品的“曲线以下，色度”作为零售定位应用积极的特征。
满足消费者的需求
LRC和其他研究表明，表征LED的CRI和CCT本身不足以完全量化的白光LED的光质量。研究人员已经证明，高亮度和高亮度的光源总是被消费者认为是高质量的，而不是仅仅在这两个指标中高出一个的光源。此外，观察员已被证明是更喜欢白色的光在温暖的体黑体轨迹和下面的轨迹冷却器的光。
类是否一个颜色指示将通过跨行业作为一个标准的定义，或被作为一种营销手段有待观察。然而，它的采用前景似乎看好，因为一些领先的LED制造商已经接受了新的衡量标准。还有一些人正在关注CCT的研究，生产出符合消费者对高质量白光的感知的色度的产品。