IR LEDs
(607)IR LEDs (infrared) are a popular solution in at least two areas: lightning for monitoring systems and wireless communication. They are available in formats that are similar to elements emitting visible light and are characterized by similar electric parameters. Low price and easy mounting are just two indisputable assets.
IR as a method of lightning
Infrared radiation, also called IR, is electromagnetic radiation with the wavelength from to 1mm up to 700nm. As such frequencies are invisible to the human eye and at the same time safe for health, they are used in wireless communication systems, sensors, and many other devices as well as in research methods**.
For example, radiation with the wavelength from 840nm up to 960nm is used as lighting recorded only by special cameras. These devices make it possible to conduct observation in (apparent) darkness, e.g. in monitoring systems (CCTV) or camera traps(maintenance-free cameras triggered by motion sensors). Thanks to the “invisibility” of infrared radiation, it can be used in many alarm systems. In the automotive sector, miniature sources of infrared radiation are used as non-invasive ICMS lightning (in-cabin monitoring system). Thanks to them, the on-board computer analyses the driver’s behaviour even at night: in case of danger (when the driver falls unconscious) ICMS automatically sets the alarm on and gradually brings the car to a full stop. In this area, IR LEDs are also used to illuminate the surroundings for sensors monitoring traffic around the car. Another related application are interfaces recognizing user’s gestures – they are also based on registering image in the spectrum of infrared radiation.
Fig. 1. Visible light, recorded by CCD and emitted by LEDs IRIncluded values.
Chart (Fig. 1) illustrates the comparison of averaged and included values for the following spectrum variants: human eye responsiveness (red line); responsivity of a typical CCD used in CCTV (blue line); the emission of infrared light by sample IR LEDs – yellow line (840-870nm models), purple line (920-960nm models).
Infrared radiation in wireless communication
Diodes emitting infrared radiation are used in wireless data transmission. A typical application are remote TV controls. However, many products available from TME are characterized by power that is higher than required by a typical TV remote control.
Transmission of data using infrared radiation signals is used in production plants whereit is applied in M2M communication (machine-to-machine). Another area where high power IR LEDs serve as transmitters are panels used for wireless transmission of sound (in digital form). They are often installed in lecture halls, cinemas, and theatres, where they transmit the signal from interpreters to receivers/headsets during international conferences, film, theatre, and opera festivals, etc. Although this transmission method has lost some of its popularity in the last decade, its great advantage is easy implementation (temporary installations) as well as immunity to EMC that may be caused by mobile phones and stage equipment.
Most of microcontroller platforms (AVR, PIC, Arduino etc.) and single-board systems have open source libraries enabling the transmission of instructions using standard protocols of transmission in infrared radiation (SIRC, RC5, RC5, etc.) From the technical point of view, connecting IR LEDs to control circuit e.g. via a microcontroller is not problematic because a standard transistor can function as a driver. Of course, it is a simplified example – in most cases a specially designed system enabling to control the emission with high frequency would be the best solution.
It needs to be taken into account that communication with the use of infrared radiation is often impossible (or significantly limited) in sunny spots.
Crucial parameters of IR LEDs
In the specification of products from this category, you can find a range of values typical for LEDs – power, maximum current, operating voltage, mounting method. Infrared elements (especially when used as a form of lighting) are often installed on matrices – this means that SMD packages are a popular variant.
Depending on the device, a demand for a space lit by infrared radiation will be different. In order to send signals controlling or observing the driver via ICMS, a narrow angle of emission is required, while the illumination for monitoring should cover the whole area observed by the camera. This is whyLEDs are characterized by a viewing angle from od 3° do 160° – this value is usually listed among basic parameters of each element.
The wavelength of emitted radiation may occur extremely crucial. In the case of lightning it has to be in accordance with the characteristics of the sensor used, whereas in devices for communication you have to remember about the compatibility between the transmitting and receiving elements. IR receivers are characterized by selectivity – thanks to this, they are immune to interference (sources of visible light). This means that an IR LED has to be adjusted so that its radiation is recorded by the optoelectrical element. Eventually, for many applications the LED optic power is a key factor. The reach of transmission as well as the intensity of illumination are dependent on it. At TME, you can find IR LEDs with the power starting from 0.2mW (used in energy-saving sensors) to products whose power exceeds 1W (elements typical for CCTV used at night).
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