LuminousIntensity;IV

Light intensity is defined as the luminous flux emitted per unit solid angle, in Candlelight (CandELa, cd). Generally speaking, a light source emits its luminous flux in different directions with different intensities, and the visible light radiation intensity emitted per unit solid angle in a specific direction is called light intensity.

Chromaticity

The human eye's perception of color is an intricate process. In order to quantify the description of color, international According to the visual experiments of standard observers, the Institute of Illumination (CIE) records the visual perception caused by the radiant energy of different wavelengths by the human eye, and calculates the color matching function of the three primary colors of red, green and blue. After mathematical conversion, the so-called so-called CIE1931ColorMatchingFunction(x((), y((), z(()), and according to this color matching function, several color measurement definitions have been developed subsequently, so that people can describe and use color.

According to the CIE1931 color matching function, the stimulus value of the human eye to visible light is expressed as XYZ, which is converted by the following formula The x,y value, or CIE1931 (x,y) chromaticity coordinates, through this unified standard, the description of color can be quantified and controlled.

x,y:CIE1931 ChromaticityCoordinates

However, since the color gamut constructed with (x,y) chromaticity coordinates is non-uniform, It is difficult to quantify the color difference, so CIE converted the CIE1931 chromaticity coordinates in 1976, so that the color gamut formed is a nearly uniform chromaticity space, so that the color difference can be quantitatively expressed, that is, the CIE1976UCS (UniformChromaticityScale) chromaticity coordinates, It is represented by (u',v'), and the calculation formula is as follows:

Dominant wavelength (λD)

It is also one of the ways to express color. y), mark it on the CIE chromaticity coordinate diagram (as shown in the figure below), connect the chromaticity point of the E light source (chromaticity coordinates (x, y) = (0.333, 0.333)) and this point and extend the connecting line, The wavelength value where this extension line intersects with the spectral locus (horseshoe shape) is called the dominant wavelength of the DUT. However, it should be noted that the same dominant wavelength will represent multiple different chromaticity points under this labeling method, so it is more meaningful when the chromaticity point of the DUT is adjacent to the spectral locus, and white LEDs cannot be used in this way. Describe its color properties.

Purity

It is an auxiliary representation when describing the color by the dominant wavelength, in percentage, it is defined as the color of the test piece The percentage of the linear distance between the degree coordinates and the chromaticity coordinates of the E light source and the distance from the E light source to the spectral locus (SpectralLocus) chromaticity coordinates of the main wavelength of the DUT. The higher the purity, the closer the chromaticity coordinates of the DUT are to its The spectral color of the dominant wavelength means that the higher the purity of the DUT, the more suitable it is to describe its color characteristics with the dominant wavelength. LED is an example.

ColorTemperature

The radiant energy distribution of a light source is similar to the radiant energy distribution of a standard black body (BlackBodyRadiator) at an absolute temperature At the same time, the chromaticity of the light source is the same as the chromaticity of the black body radiation. At this time, the chromaticity of the light source is represented by the corresponding absolute temperature. This temperature is called the color temperature (ColorTemperature), and the blackbody radiation at each temperature presents the Chromaticity can be plotted on the chromaticity diagram, called the PlanckianLocus. The higher the temperature of the standard black body, the more blue stimuli the radiated light will produce to the human eye, and the less red stimuli. However, in actual measurement, no light source has the same radiant energy distribution as a black body. In other words, the chromaticity of the light source to be measured usually does not fall on the Planckian locus. Therefore, it is calculated that the chromaticity coordinates of the light source to be measured are closest to a certain coordinate point on the Planckian locus, and the black body temperature of this point is defined as the correlated color temperature (CCT) of the light source, usually CIE1960UCS (u, v) color Find it from the degree diagram and describe it with the color difference △uv. It should be noted that this representation is meaningful only when the chromaticity of the light source is close to the Planckian locus, so for LED measurement, it is only applicable to the description of the color of white LEDs.