Electronic circuits usually need to transmit their working status, and indicator lights become a simple way to meet this requirement. In lighting solutions, LED lights consume less energy than traditional light sources. The low energy consumption of LED lights is a significant advantage in embedded system instruments where battery power may be very valuable.
If a basic signal system with only three colors of red, yellow, and green is needed for work, a simple RYG indicator light can meet the requirements. In this case, a red light indicates danger or a stop, while a green light indicates that all systems are operating normally. The RYG system is a traditional solution used for basic instrument panels and industrial signal towers.
The red, green, and blue (RGB) LED indicators light up in different colors according to the desired state, thus achieving visual display function. RGB LED indicator lights provide rich colors and more intuitive subtle information. For example, the temperature range in the gradient bar requires different shades of color to represent temperature levels.
In addition, RGB LED indicator lights can be modulated to display the desired color, enabling the functionality of two or three different indicator lights, thus requiring less space.
RGB LED indicator lights are widely used, including display screens in sturdy machinery, smart home devices, and embedded systems in industrial applications. For example, APEM's Q10/14/16/19/22 series RGB (Figure 1) can provide almost unlimited color choices with a lifespan of up to 100000 hours. RGB LED is usually the preferred choice for modern instruments and meters because this product can produce more colors while consuming less energy.
APEM Q10/14/16/19/22 series RGB LED indicator lights
APEM's RGB LED indicator lights can be controlled using pulse width modulation (PWM) technology to achieve a colorful appearance. (Image source: DigiKey)
The working principle of RGB LED
The driver controls color display by controlling the current sent to the LED. It uses 8 bits to represent the amount of color required for each channel (R, G, or B). For example, the 8-bit value of the red channel, 00000000, indicates that the final synthesis does not contain any red components. Due to each 8-bit value being composed of a combination of 0 and 1, each color module can present 28 (or 256) different values ranging from 0 to 255.
Each of these 256 values represents a subtle variation in the intensity of the red, green, and blue colors. By adjusting the 256 values of red, green, and blue elements in different combinations, circuit designers can obtain millions of color tones, specifically 256 x 256 x 256, or 16.7 million colors (Figure 2).
Cube Mapping Model for RGB Colors
Figure 2: RGB color model mapped to cube. The horizontal x-axis represents red values increasing to the left, the y-axis represents blue values increasing to the lower right, and the vertical z-axis represents green values increasing to the upper right. The origin located at the hidden vertex corresponds to black. (Image source: SharkD, CC BY-SA 4.0); Wikimedia Commons）
For example, the three components of the RGB values for magenta are set as follows: R: 255, G: 0, B: 255. At the same time, the RGB values of light purple are R: 223, G: 255, and B: 0.
To make the RGB LED indicator light display a specific color, it is necessary to fine tune the intensity of the red, green, and blue components by adjusting the power delivered to each color module. There are two methods for dynamic dimming of LED: constant current reduction (CCR) and pulse width modulation (PWM).
The CCR method changes the light output by reducing the current sent to the LED. This method is both simple and has some advantages. On the other hand, the PWM method maintains a constant current, but instead of continuously delivering current to the LED, it delivers it in a fast pulse manner, turning on and off the LED multiple times per second. The intensity of light emitted by an LED is directly proportional to the time the current is turned on, which is called the "duty cycle".
PWM is a particularly useful technique for controlling RGB LED indicator lights, as it allows for precise control over the final color output. In addition, this technology is also easy to use microcontrollers for digital control, switching outputs between high and low levels.
Aesthetic Design of RGB LED Indicator Light
If indicator lights are to be used in the display screens and control panels of electrical instruments and human-machine interfaces (HMI), they need to be more fully integrated with the equipment. Traditional dual pin LEDs usually need to be fixed on a sturdy base and typically protrude from holes on the panel. The prominent LED indicator lights may not match the aesthetic appeal of the device in the designer's mind. In addition, there is a risk of damage to the protruding part of the indicator light.
On the other hand, panel mounted indicator lights can be fixed on the panel, simplifying design and installation. In this case, the border serves as an installation bracket while ensuring visual aesthetics. The border scheme has a polished texture to prevent the LED from being exposed from the panel and easily damaged.
Even in the border scheme, RGB LED indicator lights can be installed with embedded or protruding borders. The flush frame is flush with the panel, giving it a stylish and modern appearance. In contrast, LED lampshades with raised borders will slightly protrude from the panel surface, forming a slight raised structure. If you need to observe the displayed colors from different angles, this slight bulge is particularly useful. This raised border is easier to identify when installed in sunny outdoor environments or industrial environments with glaring light. How to choose a border ultimately depends on the specific application. In poorly lit environments, it is required that indicator lights be clearer and more visible, so raised indicator lights are a better choice. If design engineers only consider aesthetics, then embedded installation is a better choice.
In addition to the frame, the panel mounted indicator light requires the circuit designer to determine the panel opening that can accommodate the indicator light in terms of mechanics. To speed up the installation process, a snap fit installation can be used, but this installation method requires more precise cutting. In addition, the indicator light can be screwed into the panel through threads to improve safety, especially in environments prone to severe vibrations. The size of panel openings may vary. APEM's Q series RGB LED indicator lights offer 10mm, 14mm, 16mm, 19mm, or 22mm openings and options for flush or protruding borders.