LED technology: How to choose the right color temperature to get satisfactory white light illumination?

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 LED Cube light source. The observer evaluated the white wall area directly opposite the surface and the paint color on the table and the X-Rite ColorChecker color. White block in the card.

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).