RGB LED (4-pin) Symbol
Definition: The RGB LED (4-pin) symbol represents a four-terminal Light Emitting Diode package containing three separate LED dies — Red (R), Green (G), and Blue (B) — sharing a Common anode or Common cathode pin, depicted in circuit diagrams with a Common pin and individual R, G, B cathode (or anode) pins, used to produce any visible colour by mixing the intensities of the three primary-colour emitters.
Also known as: RGB LED, tricolour LED, full-colour LED, 4-pin LED, common cathode RGB LED, common anode RGB LED, colour LED.
What the RGB LED (4-pin) symbol means
The RGB LED (4-pin) symbol denotes a single LED package that integrates red, green, and blue LED junctions. The four-pin package has one Common pin (either common anode — connected to V+, or common cathode — connected to GND) and three individual colour pins (R, G, B). By controlling the current through each colour pin independently (via PWM or current-limiting resistors), any colour in the visible spectrum can be approximated by additive colour mixing.
In circuit diagrams, the RGB LED symbol is drawn to show the Common pin on one side and R, G, B on the other, making it clear that three separate current paths exist within one physical package. The symbol identifies whether the device is common anode or common cathode — a critical distinction for driving circuit polarity and microcontroller GPIO configuration.
How to identify the RGB LED (4-pin) symbol
The RGB LED (4-pin) symbol is drawn as a diode triangle-and-bar symbol (representing one LED die) with two parallel emission arrows, plus additional colour channel annotations or three stacked diode symbols sharing the common pin. In simplified block representations it appears as a rectangle with the Common pin on the left and R, G, B pins on the right. The presence of three separate output pins (R, G, B) plus one Common pin is the key identifier distinguishing this from a simple single-colour LED (two-pin) or a bicolour LED (three-pin).
Function in a circuit
Each of the three LED dies in an RGB LED requires its own current-limiting resistor (or PWM duty-cycle control) to set the luminous intensity of the red, green, or blue emission. The forward voltage of each die differs: red LEDs have a lower Vf (~1.8–2.2 V), while green and blue have higher Vf (~3.0–3.5 V). Colour mixing is achieved by PWM (Pulse Width Modulation) control: varying the duty cycle of each colour's drive signal changes its perceived brightness, allowing the eye to integrate the combined light into a mixed colour. Full brightness on all three channels produces white light.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-05 defines LED symbols as a diode symbol with two emission arrows (photon radiation lines). A 4-pin RGB LED is represented as three parallel LED symbols sharing a common terminal line, with R, G, B annotations. The common anode or cathode configuration is indicated by the polarity orientation of the diode triangles. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 defines the LED as a diode symbol (triangle pointing to a bar) with two arrows indicating light emission. RGB LEDs follow the same convention with three colour-annotated LED diode symbols and a shared common terminal. The designator is LED or D (e.g. D1 for the first LED device). |
| Key difference | IEC 60617 and ANSI Y32.2 / IEEE 315 use essentially the same LED symbol — a diode (triangle+bar) with emission arrows. Both allow multi-die packages to be shown as multiple diode symbols sharing a common pin. The main drawing difference is that IEC omits the diode triangle fill (outline only) while some ANSI traditions use a filled triangle, but both are acceptable in practice. |
Terminals / pins
| Pin | Name |
|---|---|
| common | Common |
| r | R |
| g | G |
| b | B |
Typical values
Forward voltage (Vf): Red ~1.8–2.2 V, Green ~3.0–3.5 V, Blue ~3.0–3.5 V. Forward current (If): typically 20 mA per channel continuous; 30–100 mA peak. Supply voltage: 3.3 V–5 V (with current-limiting resistors). Current-limiting resistor: R = (Vsupply − Vf) / If; e.g. (5 V − 2.0 V) / 0.020 A = 150 Ω for red at 5 V. Luminous intensity: typically 1,000–6,000 mcd per colour channel.
Where the RGB LED (4-pin) symbol is used
- Status indicator LEDs on Arduino and Raspberry Pi projects showing system states as different colours (red=error, green=ok, blue=connected)
- Mood lighting and decorative lighting where PWM colour mixing creates dynamic colour effects
- Backlighting for LCD displays and keypads, allowing backlight colour to change with UI state
- Wearable electronics and costume lighting using small RGB LED packages driven by microcontrollers
- Traffic light simulators and educational electronics kits demonstrating colour mixing and PWM
- RGB LED strips (where each module contains one RGB LED pixel) for architectural and home automation lighting
Example
In an Arduino colour controller schematic, the RGB LED (4-pin) symbol's Common cathode pin connects to Arduino GND; the R pin connects through a 150 Ω resistor to Arduino PWM pin D9; G through a 100 Ω resistor to D10; B through a 100 Ω resistor to D11 — the different resistor values compensate for the different Vf and luminous efficiency of each colour to achieve perceptually white light at maximum brightness.
Key facts
- The RGB LED (4-pin) has four pins: Common (anode for common-anode type, or cathode for common-cathode type), R (red cathode or anode), G (green cathode or anode), and B (blue cathode or anode).
- Common cathode RGB LEDs connect the Common pin to GND; the R, G, B pins are driven HIGH through current-limiting resistors. Common anode types connect Common to V+ and drive R, G, B LOW.
- Each colour channel requires a separate current-limiting resistor calculated as R = (Vsupply − Vf) / If; red typically needs a higher resistance than green and blue because its lower Vf (1.8–2.2 V vs 3.0–3.5 V) results in higher current at the same supply voltage.
- PWM (Pulse Width Modulation) control adjusts each channel's perceived brightness by rapidly switching the current on and off; at 50% duty cycle the LED appears half-brightness to the human eye.
- Additive colour mixing: Red + Green = Yellow; Red + Blue = Magenta; Green + Blue = Cyan; Red + Green + Blue = White. This is additive mixing (light addition), opposite to subtractive mixing (paint/pigment).
- The LED designator on schematics is D (for diode) per IEEE 315; e.g. D1 for the first LED. Some designers use LED1 as the reference designator for clarity.
- Addressable RGB LEDs (WS2812, SK6812) integrate the driver IC within each LED package and communicate over a one-wire serial protocol, making them functionally different from the simple 4-pin RGB LED described here.
Frequently asked questions
What does the RGB LED symbol mean in a circuit diagram?
The RGB LED (4-pin) symbol represents a single LED package containing red, green, and blue LED dies sharing a Common pin. By independently controlling the current or PWM duty cycle through the R, G, and B pins, any visible colour can be produced by additive mixing. The Common pin is either the common anode (V+) or common cathode (GND).
What does the RGB LED 4-pin symbol look like on a schematic?
The RGB LED symbol appears as a rectangle or combined diode symbol with one Common pin on one side and three colour pins (R, G, B) on the other side. In full schematic detail, three LED symbols (each showing a diode triangle-and-bar with emission arrows) share the Common terminal, with R, G, B labels on the individual anodes or cathodes.
What is the difference between a common cathode and common anode RGB LED?
In a common cathode RGB LED the Common pin connects to GND, and the R, G, B pins are driven HIGH (through resistors) to illuminate each colour. In a common anode RGB LED the Common pin connects to the positive supply (V+), and the R, G, B pins are driven LOW to illuminate. Using the wrong polarity will prevent the LED from lighting.
What resistors do I need for an RGB LED with Arduino?
Use R = (Vsupply − Vf) / If for each colour channel separately. At 5 V supply with If = 20 mA: red (Vf ≈ 2.0 V) needs (5−2.0)/0.02 = 150 Ω; green (Vf ≈ 3.2 V) needs (5−3.2)/0.02 = 90 Ω (use 100 Ω); blue (Vf ≈ 3.3 V) needs (5−3.3)/0.02 = 85 Ω (use 100 Ω). Always use nearest standard resistor value, rounding up.
How do I control the colour of an RGB LED?
Control each colour channel's brightness using PWM (Pulse Width Modulation) on a microcontroller. On an Arduino, analogWrite(pin, 0–255) sets duty cycle 0–100% on each channel (D, R, G, B). Mixing R=255, G=0, B=0 gives red; R=255, G=255, B=0 gives yellow; R=255, G=255, B=255 gives white (with matched resistors).
What is the difference between a 4-pin RGB LED and a WS2812 addressable LED?
A 4-pin RGB LED requires separate PWM signals and current-limiting resistors for each colour channel from the microcontroller. A WS2812 (NeoPixel) addressable LED integrates the driver IC inside the LED package, requires only one data wire regardless of chain length, and receives colour data via a one-wire serial protocol — making it far simpler to control in large arrays.
What standard defines the RGB LED symbol?
IEC 60617-05 defines the LED symbol as a diode with two emission arrows; RGB LEDs are shown as three such symbols sharing a common terminal. ANSI Y32.2 / IEEE 315 uses the same diode-with-arrows convention. The component is designated D (or LED) in both standards, with the specific type labelled RGB or annotated with colour identifiers.
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