# Experimental Study on Chromaticity Control in Visible Light Communication Systems
## 1 Introduction  
As a dual-function white LED for lighting and communication, it is important to consider the influence of the light source's color on the human eye in addition to its communication performance. Creating a lighting environment with a positive psychological, physiological, and visual impact on individuals is crucial [1, 2]. The color temperature of the light source has a significant impact on the human nervous system [3]. Cold-colored light sources can potentially stimulate the nervous system, and in high color-temperature environments, a person's heart rate and pulse accelerate, blood pressure increases, and mental excitement occurs. On the contrary, warm-colored light sources have effects such as sothing emotions, reducing stress, and lowering heart rhythm and pulse [4]. In terms of psychological perception, low color temperature light sources (warm color light) make people feel warm, while high color temperature white light (cold color light) makes people feel cold [5]. To achieve dynamic changes in LED color temperature, it is necessary to quantitatively control the chromaticity of the light source. Studying LED light sources with adjustable color temperature in visible light communication systems has a certain significance. Adjusting the color temperature of LEDs according to different environments can make people feel comfortable with the light environment and create a healthy lighting environment. Generally, the color temperature range of indoor lighting is 3000 K\(\sim\)6500 K [6]. Using light sources with different color temperatures in different situations can meet people's psychological and physiological needs. So, making the color temperature of the lightsource in visible light communication systems adjustable and controlling the chromaticity is currently a topic of great interest in research. There have been studies on the use of multi-color LEDs for transmitting information in visible light communication systems. In 2015, [PERSON] et al. constructed an RGB LED visible light communication video transmission system and completed an experiment on video data stream transmission at a transmission rate of 1.5 Mbps [7]. In 2018, [PERSON] et al. conducted an experiment on an indoor visible light communication system using RG-BCY LEDs and the wavelength division multiplexing (WDM) technique. The experiment attained a communication rate of 10.72 Gb/s and a communication distance of 1 m [8]. In 2018, [PERSON] et al. achieved a 10.2 Gbps three-channel visible light communication experiment using RGB LEDs and the WDM technique [9]. In the next year, the team used four different colored LEDs as light sources and the OFDM modulation method to complete an experiment on 15.73 Gbps VLC reliable transmission on a 1.6 m link [10]. In 2020, [PERSON] et al. accomplished a transmission experiment via multi-color LEDs over a 1.2 m underwater link using DMT modulation and WDM techniques, achieving a communication rate of 20.09 Gbit/s [11]. In 2022, [PERSON] et al. used three LEDs and five micro-LEDs, alongside wavelength division multiplexing technology to successfully achieve a visible light communication experiment with a total communication rate of 25.20 Gbps when the communication distance is 25 cm [12]. In 2022, [PERSON] developed an LED visible light communication control system capable of achieving lighting effects and transmitting signals up to 3 m away with a transmission speed of 56,000 bit/s and low BER [13]. In the field of visible light communication, multi-channel visible light communication systems using multiple monochrome LEDs have achieved high communication rates, but there is no color control mechanism. The color of the light emitted by multiple LEDs poses a certain threat to human eyes [14; 15]. Research shows that the color and brightness of the light source have an impact on the adjustment ability of the ciliary muscle of the human eye [16], which can cause visual fatigue and discomfort and easily lead to myopia.