What is the SDCM of your fixtures and lamp beads?

SDCM has quickly entered the eyes of lighting design, and more and more people will ask "What is the SDCM of your lamps and lamp beads?"

The actual diagram of the SDCM approximates "the relative displacement of one actual chromaticity coordinate from another typical chromaticity coordinate."

The prevalence of this indicator has led to another requirement that has not yet been included in any standard: "How to quantitatively assess the uniformity of a spot of a color luminaire."

The fact that manufacturers of luminaires generally do not disclose is that the size of the RA chip in RGB or RGBW, RGBAW luminaires, the law of luminescence and the law of luminescence of GB are different from the law of illumination of W, because light travels in a straight line, In the same lens, the trajectories of the RGBAW light are not completely overlapped. Taking the small red chip and the blue-green chip as an example, the spot illuminated by the RGB lamp (not discussing the design of the lens itself) is generally uniform in the middle portion and green in the outer ring.

The main factors that generally affect color mixing are:

1. Chip size

2. The number of chips in a single LED package

3. The actual package style of the LED

4. The relative relationship between the actual luminous surface size and the illumination distance of a luminaire containing multiple LEDs

5. Select lens angle

6. Use lens and LED matching

7. Uniform distribution of multiple circuits in the presence of multiple independent circuits

It is not difficult to get back to the origin and use of SDCM indicators. These are two similar mathematical propositions, which are based on a keyword in the mathematical statistics theory - standard variance, used to indicate the degree of dispersion of the data set: general calculation The steps are:

1. Find the difference between each number and the mathematical mean of the sample series, and call the mean difference;

2. Calculate the square of each difference, called the variance;

3. Find the sum of them and divide by the number of samples (number of items -1) to get the mean square error.

4, then open the root number to get the standard variance!

By definition of standard deviation, we can extend it and define a definition: chromaticity standard deviation, which refers to a standard deviation of the chromaticity coordinate samples of a luminaire whose normal illumination distance is regularly taken. .

Fully open a mixed-color luminaire, project it on a plane with a long distance from normal application, and uniformly mesh the area from 100% light intensity to 5% light intensity on the plane. At the point corresponding to the grid, use color. The product counts the chromaticity coordinates, and has n*m group data. Each group of data is (Xij, yij), and then input into a calculation table to calculate the average chromaticity coordinates:

Then use the standard variance formula to calculate in the table to get the standard deviation of the chromaticity.

Here, η can be RGB, or RGBW, or RGBAW, etc., and can even be combined with multi-color warm white light mixing ACSW.

Let's take a three-color 3WRGB minimum-stained floodlight as an example. Let's assume that the light distribution is 16-degree beam angle (50% light intensity), 33-degree light spot angle (10%) light intensity, and projected to 3M far-mixed light spot. For example, the circular spot here is generally n=m, so use an 11*11 matrix grid to collect the CIE of each point for the acquisition rule.

1931 chromaticity coordinates:

Then calculate the average x coordinate and y coordinate of the corresponding value:

The standard deviation of the chromaticity of the RGB color mixing lamp is available:

Referring to the selection criteria of SDCM<5, if the calculated SDC value is greater than 0.005, the color mixture is considered to be not very good, and the larger the value is, the worse the color mixture uniformity is. If the SDC value is less than 0.005, the lamp is considered to be suitable for stage dyeing illumination. Also suitable for other architectural and landscape uses.