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2024-12-09
D65 light source is a standard light source in the D series specified by CIE, and is also the most commonly used color light source in the current standard light source box. D65 light source and D50 light source are both D series light sources, so what is the difference between D65 light source and D50 light source? This article introduces D65 light source and its difference with D50 light source.
D65 light source
D65 light source is a standard light source in the D series specified by CIE. Among the D series standard lighting bodies, CIE recommends D65 as the preferred lighting body. D65 represents the average daylight with a correlated color temperature of 6500K. It is an average result of measuring the daylight in the northern window of the northern hemisphere on a cloudy day regardless of the season and time of the day. D65 is an indispensable standard light source in many standards such as ISO 105-A01 "General Rules for Testing Color Fastness of Textiles" and ASTM D1729 "Standard Method for Visual Evaluation of Opaque Materials". However, due to the special spectral power distribution of D65, there is currently no artificial light source that can emit light with the same spectral power distribution as D65, and it can only be approximately simulated. In most standard light boxes, two high color rendering fluorescent lamps are used to simulate the D65 light source, while in the GretagMacbeth SPLⅢ standard light box, tungsten filter technology is used to simulate the D65 light source with two halogen tungsten lamps.
Standard illuminant D represents the relative spectral power distribution of sunlight at various phases, also known as typical sunlight or reconstructed sunlight. Since standard illuminant D has a relatively close relative spectral power distribution to actual sunlight, and is more consistent with the chromaticity coordinates of actual sunlight than standard illuminants B and C, CIE recommends the use of standard illuminant D first. Standard illuminant D is divided into several types such as D50, D55, D65, and D75. When standard illuminant D65 cannot be achieved, it is recommended to use standard illuminants D50, D65, and D75 as much as possible. Their relative spectral power distribution curves are shown in the figure.
The correlated color temperatures of standard illuminants D50, D55, D65, and D75 are 5000K, 5500K, 6500K, and 7500K, respectively. As can be seen from the figure above, the spectral power distribution curves of standard D50, D55, and D65 are very similar to those of D65. The relative spectral distribution curves of standard illuminants A, B, C, and D65 are shown in the figure below. As can be seen from the figure, the relative spectral power distribution curves of standard illuminants A and B, C, and D65 are quite different.
In order to simulate the spectral power distribution of the D65 light source and achieve better color inspection results, the D65 light source needs to meet the relevant requirements of the International Organization for Standardization ISO.
1. Color temperature requirements
The color temperature of the D65 standard light source used for color matching should reach the specified color temperature, which cannot be higher than 500K. However, some strict companies require the color temperature range of the standard light source used for color matching to be within 200K. For example, if a D65 light source lamp is used, its color temperature must be guaranteed to be in the range of 6300-6700K. If the color temperature does not meet the requirements, it cannot be used as a color matching light source.
2. Color rendering requirements
Color rendering refers to the ability of a light source to restore the color of an object. The color rendering of different light sources is very different. A light source environment with insufficient color rendering will cause a large deviation in our color measurement results. The D65 light source lamp used for color measurement is usually required to have a color rendering index of more than 90.
3. Illumination requirements
We know that without light or when the light is very dim, it is difficult for us to observe the color of an object. The light and dark feeling here can be expressed by the illumination of the light source. If the illumination of the light source does not meet the standard, the detected color will also be distorted. Since the size of the color matching light box is inconsistent and the distance from the sample is different, the brightness of the D65 light source tube configured in different color matching light boxes will also be different, so as to keep the illumination basically consistent.
4. Uniformity requirements
If the light source in the light box is uneven, the color it presents will also have a certain deviation. In order to ensure the accuracy of the color matching results, the D65 light source tube of the color matching light box needs to emit light safely and stably, and can evenly and softly illuminate the surface of the object being illuminated.
The standard illuminant D represents the relative spectral distribution of sunlight at different time phases. The D50 standard illuminant refers to the relative spectral power distribution of sunlight with a color temperature of about 5000K, while D65 refers to the relative spectral power distribution of sunlight with a color temperature of about 6500K. In order to better simulate the lighting effect of D50 and D65 light sources, it is necessary to use artificial standard light sources D50 and D65. Therefore, the main difference between D50 and D65 light sources is the color temperature.
D65 light source is also known as the international standard artificial daylight (Artificial Daylight). Its color temperature is 6500K (color temperature). It is used as the standard light source for evaluating the color of goods. Especially during the night shift, it is particularly important to use standard light sources to detect color deviations of goods. In addition to the D65 standard light source that must be included in the multi-light source standard light source box, there are also TL84, CWF, UV, F, A, U30, HOR and other light sources. It has the function of testing the metamerism effect.
The color temperature of D50 light source is 5000K, which is recognized as the standard color temperature (ICC standard) by the world printing industry and is usually used in the field of printing or pre-publishing. Its conditions are similar to those under daylight, and although the color is relatively normal, it is not easy to find the change of yellow ink.
D65 and D50 usually refer to two standard light sources, including color temperature, color rendering index, metamerism index, illumination, etc. The biggest difference between them is that the color temperature of D65 is 6500K, the light is blue, which is closer to the color of ordinary fluorescent lamps; the color temperature of D50 is 5000K, and the light is slightly red. At present, D50 is basically used as the standard observation condition internationally, but in China, D65 is still one of the standard color temperatures widely used.
