IR Transmitter LED Symbol
Definition: The IR Transmitter LED symbol represents an infrared-emitting diode (IRED) in circuit diagrams, drawn as the standard diode triangle-and-bar glyph with two diagonal emission arrows indicating invisible infrared light output, standardised under IEC 60617-05 and ANSI Y32.2 / IEEE 315, with designator D and operating wavelengths between 850 nm and 950 nm.
Also known as: IRED, infrared LED, IR diode, infrared transmitter, IR emitter, infrared emitter diode.
What the IR Transmitter LED symbol means
The IR Transmitter LED symbol denotes a p-n junction diode that emits infrared radiation when forward biased. Unlike a visible LED, its emitted light is in the 850–950 nm wavelength range — invisible to the human eye but detectable by photodetectors and IR receiver modules. In schematics the symbol marks the optical output point of an infrared communication link.
In circuit diagrams, the IR Transmitter LED appears wherever a wireless infrared signal must be generated, from remote control transmitters and object-detection systems to optocouplers and proximity sensors. Its two pins — Anode (+) and Cathode (−) — establish the polarity for forward-biased emission, and the emission arrows on the symbol distinguish it from a standard rectifier diode or indicator LED.
How to identify the IR Transmitter LED symbol
The IR Transmitter LED symbol is identical in structure to a visible LED symbol: a triangle (pointing in the direction of conventional current flow, anode on the left) abutting a vertical bar (cathode). Two diagonal arrows emerge from the junction area and point away from the device at roughly 45 degrees, indicating photon emission. The symbol is visually the same as a visible LED glyph; context and labeling (e.g., 'IR', '940 nm', or 'IRED') distinguish it from a visible-light LED on a schematic.
Function in a circuit
An IR Transmitter LED conducts in the forward direction (anode positive relative to cathode) and converts electrical energy into infrared photons via electroluminescence. When pulsed at a carrier frequency (typically 38 kHz), it produces a modulated IR beam that an IR receiver module can demodulate and decode. A current-limiting resistor in series controls forward current to set the radiant intensity, protecting the diode from exceeding its maximum forward current rating (typically 100 mA continuous, up to 1 A peak for pulsed operation).
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-05 (semiconductor devices): the IR Transmitter LED uses the standard LED symbol — a diode triangle-and-bar with two emission arrows. IEC does not distinguish between visible and infrared LED glyphs; labeling or a note specifies the wavelength. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2-1975 / IEEE 315-1975: the IR emitter uses the same light-emitting diode symbol — triangle pointing to bar with two outward arrows. The ANSI symbol is visually identical to the IEC symbol for this device. |
| Key difference | The IEC and ANSI symbols for an IR Transmitter LED are visually identical — both show the diode triangle-and-bar with two emission arrows. The distinction between infrared and visible-light LEDs is conveyed by a wavelength annotation or a schematic note, not by a different glyph. |
Terminals / pins
| Pin | Name |
|---|---|
| anode | Anode (+) |
| cathode | Cathode (-) |
Typical values
Forward voltage (Vf): 1.2–1.5 V at 100 mA. Forward current (If): 20–100 mA continuous; up to 1 A peak (pulsed). Peak wavelength: 850 nm, 880 nm, or 940 nm. Half-angle: 15°–60° depending on lens. Radiant intensity: 10–100 mW/sr at rated current.
Where the IR Transmitter LED symbol is used
- Remote control transmitters for TVs, set-top boxes, air conditioners, and audio equipment
- Optocoupler input stages for galvanic isolation between circuits
- Proximity and object-detection sensors (reflective or through-beam configurations)
- Infrared serial communication links (IrDA) for short-range data transfer
- Line-follower robot IR emitter-receiver pairs
- Security beam-break intrusion detectors
Example
In an Arduino-based IR blaster schematic, an IR Transmitter LED (940 nm) has its Anode (+) connected through a 47 Ω current-limiting resistor to GPIO pin D3 of the Arduino, and its Cathode (−) connected to GND. When D3 is pulsed at 38 kHz, the LED emits a modulated beam decoded by a TSOP38238 receiver in the target device to replicate remote-control commands.
Key facts
- The IR Transmitter LED symbol is the standard IEC 60617-05 / ANSI Y32.2 LED glyph — a diode triangle-and-bar with two diagonal emission arrows — used for both visible and infrared emitters; wavelength annotations distinguish them.
- The Anode (+) pin connects to the positive supply (through a current-limiting resistor) and the Cathode (−) pin to ground; forward current flows from anode to cathode to produce infrared emission.
- Typical forward voltage is 1.2–1.5 V and forward current is 20–100 mA continuous; exceeding the rated current without pulse-width limiting destroys the junction.
- Peak emission wavelength is commonly 940 nm (matched to most IR receiver ICs) or 850 nm (higher radiant power, used in surveillance and long-range links).
- Pulsing the IR LED at 38 kHz allows a matched IR receiver IC (e.g., TSOP38238) to demodulate the carrier and reject ambient IR noise from sunlight and incandescent lamps.
- The designator for an IR Transmitter LED in a schematic is D (diode) per IEC 60617 and ANSI Y32.2 / IEEE 315, often suffixed, e.g., D1.
- Radiant intensity, measured in mW/sr, determines range; a narrow-angle (15°) IR LED achieves greater point-to-point range than a wide-angle (60°) LED of the same power.
Frequently asked questions
What does the IR Transmitter LED symbol look like?
The IR Transmitter LED symbol shows a diode triangle (anode on the left) pointing to a vertical bar (cathode) with two diagonal arrows pointing outward and away from the junction to indicate light emission. It is visually identical to a visible LED symbol; the label 'IR', a wavelength annotation such as '940 nm', or the component part number identifies it as an infrared emitter on the schematic.
What does the IR Transmitter LED symbol mean in a circuit diagram?
The IR Transmitter LED symbol means that when forward biased — anode positive relative to cathode — the component emits infrared light at its rated wavelength (typically 850–950 nm). In a circuit diagram it marks the optical output of an infrared communication or sensing link.
Which pin is the anode and which is the cathode on an IR LED symbol?
On the IR Transmitter LED symbol, the anode (+) is on the flat base of the triangle (left side), and the cathode (−) is at the vertical bar (right side). Current flows from anode to cathode, and the IR light is emitted from the junction area. On physical IR LEDs, the cathode lead is typically the shorter leg or identified by a flat on the dome.
What is the difference between an IR LED symbol and a regular LED symbol?
The IEC 60617-05 and ANSI Y32.2 / IEEE 315 glyph is identical for visible and infrared LEDs — both show a diode triangle-and-bar with two emission arrows. The distinction is made by a wavelength note (e.g., 850 nm or 940 nm) or the label 'IR' on the schematic, not by a different symbol shape.
What standard defines the IR Transmitter LED symbol?
The IR Transmitter LED uses the LED symbol defined in IEC 60617-05 (semiconductor devices) for IEC-standard schematics, and in ANSI Y32.2-1975 / IEEE 315-1975 for North American schematics. Both standards use the same diode-with-emission-arrows glyph; neither specifies a separate infrared variant.
What resistor value do I need with an IR Transmitter LED?
Calculate the series resistor as R = (Vsupply − Vf) / If. For a 5 V supply, Vf = 1.2 V, and If = 100 mA, R = (5 − 1.2) / 0.1 = 38 Ω; use the nearest standard value of 39 Ω. For pulsed operation at 38 kHz, peak currents up to 500 mA are permissible on many IR LEDs, dramatically increasing range, but the resistor must be sized for the duty cycle.
What is the designator for an IR Transmitter LED in a schematic?
The IR Transmitter LED uses the designator D (diode) per IEC 60617 and ANSI Y32.2 / IEEE 315, typically with a numeric suffix, e.g., D1 or D2. Some designers use the prefix IR or IRED informally, but D is the standardised reference designator letter.
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