In general, many people take it for granted that white light is located on the black body radiation trajectory and is divided into warm white and cool white depending on the color temperature. So, the question is, is the point on the black body radiation trajectory really the white light perceived by the human eye? 
In 2013, research by researchers Rea and Freyssinier showed that the white light trajectories of different color temperatures did not completely coincide with the black body radiation trajectories. In the experiment, the observer evaluated the white inner wall in the light box. The illumination source includes six groups of color temperatures of 2700K, 3000K, 3500K, 4100K, 5000K and 6500K. Each group of color temperature groups is divided into seven different sources of Duv values.
As shown in the figure below, one of the seven light sources has a chromaticity on the black body radiation trajectory, and the chromaticities of the other six light sources are more evenly distributed on the isochromatic temperature line of the set of light sources. After analyzing the evaluation data, it is found that when the color temperature of the light source is lower than 4000K, the observer agrees that the white light chromaticity coordinates are below the black body radiation track, and when the light source color temperature is higher than 4000K, the evaluated white light chromaticity coordinates are located in the black body radiation track. Above. Therefore, the point on the black body radiation trajectory is basically not the white light perceived by the human eye.
In 2014, Smet et al. conducted an experiment to study the whiteness of objects. The research object is a three-dimensional cube illuminated by a projector in a light box. The observer can control the projector to change the color of the cube to adjust the white light that best meets the observer's expectations. The experimental results are shown in the following table. The experimental data of the two psychophysical methods indicate that the best white light expected by the observer is a light source with a color temperature of about 6000K and a Duv negative value, and when the brightness of the light source is higher and higher, the observer The perceived white light color temperature is getting lower and lower.
Based on previous studies, researchers at Zhejiang University conducted relevant white light evaluation experiments. As shown in the figure below, the experiment was carried out in a living room environment. The illumination source was a tunable spectral THOUSLITE LEDCube source. The observer evaluated the white wall area directly opposite the surface and the paint color card on the table and the X-Rite ColorChecker color card. White block in the middle.
The LED adjustable light source illumination color temperature is set to five kinds of 6500K (standard illumination body D65), 5000K (standard illumination body D50), 4000K, 3500K and 2850K (standard illumination body A). The color appearance attributes evaluated by the observer include: the brightness of the wall surface, the vividness, the warmth attribute, and the whiteness of the specific area, the white percentage, the whiteness of the preference, and the hue component of the specific area (the portion enclosed by the red line in the figure).
The evaluation rules for hue components need to be described in detail. As shown in the figure below, the hue components of pure red, pure yellow, pure green, and pure blue are 0, 100, 200, and 300, respectively, and other colors are based on each monochrome. The proportion of the hue component is evaluated, for example, a reddish orange may have a hue component of 30, and a yellowish orange may have a hue component of 70.
In fact, the hue component has a great influence on the observer's psychological perception; the blue light source (the hue component is close to 300 or so) makes the room's psychological perception colder, brighter, less vivid and whiter; Yes, the reddish illumination source (the hue component is close to 0 or 400) makes the room feel more warm, darker, more vivid and less white.
The results of psychophysical experiments of Zhejiang University and others are very similar to those of previous studies (the actual line in the figure is the experimental result of Zhejiang University, and the dotted line is the result of Rea et al.), that is, when the color temperature of the light source is lower than 4000K, observe The white light chromaticity coordinates are considered to be below the black body radiation trajectory; when the light source color temperature is higher than 4000K, the opposite is true.
A bright room looks colder, less bright and whiter, while a darker room looks warmer, more vibrant and less white. Interestingly, when the lighting in the room is brighter, the color of the color card becomes more vivid, while the brightness of the entire room is reduced. Because of the large white wall in the experimental room, only a small part of the field of view has colored objects.
The color temperature and Duv value of the illumination source also have an effect on the color appearance of the room and objects. Illuminated light sources with high color temperatures or low Duv values ​​make rooms and objects brighter. The increase of the color temperature of the illumination source within a certain range will reduce the vividness of the room, and then the brightness will increase when the color temperature of the light source rises to 6000K. This also proves that the illumination source with a color temperature of 6000K is the most considered by the observer. Neutral white light.
In summary, these psychophysical experiments have proved that the white light chromaticity coordinates perceived by the observer are not located on the black body radiation trajectory. Therefore, to select the appropriate white light illumination, firstly, it is necessary to select the appropriate color temperature, and secondly, consider setting the appropriate light source Duv. Values, in order to help you get the satisfaction of white light.
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