How to control the color of LED lamps and the color mixture?

In recent years, solid-state LED lighting fixtures have become popular, and the author attempts to analyze the complexity of LED color technology and its control methods.

About additive color mixing

LED luminaires use multiple light sources to achieve a variety of shades and intensities. For the performing arts and lanterns industry, the addition of color mixing is a commonplace. For many years, practitioners have used luminaires with color filters to project the same area on the sky, which is not easy to control. The first smart luminaire I used was a spotlight with three MR16 sources with red, green and blue filters. In the early days, this type of luminaire had only three DMX512 control channels and no independent intensity control channels. So it is difficult to keep the color unchanged during the dimming process. Usually, the programmer of the computer light will also set a "light out color change" to easily extinguish the luminaire. Of course, there are better ways, which are not listed here.

Color control and definition

If the user does not use pure DMX values ​​to control the smart fixtures, but with some abstract control, a virtual intensity value can be used. Even if the manufacturer stipulates that the luminaire uses three DMX channels, the abstract control mode can be assigned four handles to control: the intensity value and the three color parameters.

Here I wrote "3 color parameters" instead of red, green and blue, because RGB is just a way to describe colors. Another way of describing is hue, saturation, and luminance-HSL (some people call it intensity or lightness, not brightness). Another description is hue, saturation, and value-HSV. Value is also often referred to as brightness, which is similar to Iumlnance. However, the definitions of saturation for HSL and HSV vary widely. For the sake of simplicity, the author defines the hue as the color and the saturation as the amount of the color. If "L" is set to 100%, it is white, 0% is black, then 50% of L is a solid color with a saturation of l00%. For "V", O% is black, and l00% is a solid color, at which point the saturation value must compensate for the difference.

Another effective description is CMY, which is the three primary colors, using subtractive color mixing. If white light is emitted at first, then two color filters can be used to obtain red: magenta and yellow; they remove the green and blue components of white light, respectively. In general, LED color-changing luminaires do not use subtractive color mixing, but this is still an effective way to describe color.

In theory, when controlling LEDs, you should be able to adjust the intensity and one of RGB, CMY.HSL or HSV (there are some differences between them).

About LED color mixing

The human eye can perceive light having a wavelength of 390 nm to 700 nm. The original LED luminaires only used red (about 630 nm), green (about 540 nm) and blue (about 470 nm) LEDs. These three colors cannot be mixed with every color that the human eye can see. Figure 1 is a hypothetical region based on the proposed RGB model over the entire visible spectrum.

The three vertices of the triangle fall within the high saturation red, green, and blue regions, respectively. By changing the power emitted by each LED chip , any color in the color gamut can be obtained, but this is only a theory. In fact, the color mixing effect is affected by many factors. For example, the exact wavelengths of red, green, and blue vary from lamp to lamp, and there may be large differences between them.

The gamut not only describes the hue, but also the intensity and saturation. If you quickly search for "colorgamut" via Google, you'll see circles, rings, cubes, cones, and even fruit shapes, all of which attempt to show the three-dimensional relationship of HSL.

Add more colors

With the technological innovation of LED and the price drop, more and more manufacturers have entered this market. Lighting designers are increasingly looking forward to this new light source, which increases the brightness of the luminaire and the need to control color consistency. New LED colors such as white, amber, cyan and violet are available. At first, the most popular combination was RGBA, which added an amber chip. This makes the shape of the gamut more like a rectangle, not a triangle.

Another variant is RGBW, which has a wide spectrum of white LEDs. More new fixtures add white and amber (RGBAW) to RGB.

With the continuous advancement of LED technology , chip manufacturers have also successfully produced deep red, cyan and royal blue LEDs. These colors have been applied to 7-color systems (dark red, red, amber, green, cyan, blue, and royal blue), which expands the color gamut and gives designers more color.

Controlling so many chips can be laborious; multiple combinations of chip power can achieve the same color point in the color space.

How to control these LEDs

Due to the further development of LED technology, control has become more and more complicated. Fortunately, some modern control systems can drive any type of color system in a very simple way. In addition to the intensity, the user gets different color parameters: RGB, CMY.HSL and HSV.

The author examines these possibilities through a real-life example. For example, the designer is making a musical, and is using a mixed-color luminaire to dye the sky.

There is a need to create a sunset scene on the stage, and the designer wants to change from amber to pink. Using RGB color space, cuel is amber (R=100%, G=60%, B=O%), and cue2 is pink (R=100%, G=0%, B=60%).

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