The image we see is formed in our brain based on the analysis of information from the rods and cones located in our eyes. Rods are responsible for black-and-white vision with high resolution. We perceive colors thanks to cones, which are divided into three groups. Depending on the group, the peak of their sensitivity is on red (R), green (G), or blue (B).
To create the sensation of seeing a specific color shade, you can mix red, green, and blue light in a set proportion. This principle is the foundation of color television and is used in color displays, etc. This principle is also applied in lighting.
Creating a shade from three primary colors
Powerful LEDs are produced where the semiconductor chip can emit blue or red light, depending on the type. Green LEDs, where the crystal emits light directly, have low efficiency. Therefore, powerful green LEDs are semiconductor chips with blue light, covered in phosphor, which converts this light to green.
A three-channel dimmer is used to control LEDs, operating on the principle of pulse-width modulation (PWM).
Light from different colored LEDs is mixed by the optical system of the fixture. In addition, RGB LEDs are produced, where red, green, and blue chips are located in one package. In these, the mixing of primary color emissions occurs inside the package. This simplifies the lighting fixture design and makes it more compact. The drawback of RGB LEDs is their lower power compared to separate LEDs of different colors. Therefore, RGB LEDs are mainly used in decorative lighting, such as holiday garlands.
White light from RGB
In an actual lighting fixture, the adjustment of the ratio between primary colors has some inaccuracy. Additionally, the light output from different colored LEDs depends on temperature differently. As a result, a dirty shade of white light is produced, which also changes over time.
For this reason, if pure white light is needed, LEDs based on a blue chip, where the other spectral components are created using phosphor, are typically used.
Combination of RGBW colors
When dealing with stage lighting, the color of the light changes quickly over time, and the viewer doesn't have time to notice inaccuracies in the formation of white light. Therefore, such lighting fixtures can be based on LEDs of three primary colors. But if we are talking about lighting a residential area, where the color of the light changes occasionally, white (W) is added to the RGB colors. RGBW fixtures are produced based on both separate LEDs of different colors and RGBW LEDs. In such fixtures, a four-channel dimmer is used for controlling the LEDs.
In biodynamic lighting systems (this will be discussed in a separate article), sometimes five primary colors are used. In some special lighting systems (e.g., stage or garden lighting), even more primary colors may be used. However, the setup and management of such fixtures should be carried out by trained specialists, so these systems have not yet been widely adopted.
