I sent some questions to Rajeev Thakur, regional marketing manager, of Osram Opto Semiconductors who is an expert in IR LEDs, sensors, and Advanced Driver Assistance Systems (ADAS). I wanted to get a better understanding of why IR LEDs (IREDs) work well for such systems and what they accomplish.
Why IR LEDs for ADAS
Rajeev pointed out in an email about how and why IR LEDs are used for pedestrian detection. “Most cameras work during the day when there is sunlight but struggle in dark areas. Federal regulations limit the range, field of view and intensity of visible light from automotive headlamps. By installing infrared LEDs in the headlamp (along with visible), the range, field of view and performance (ability to detect objects) of cameras used in automobiles for ADAS and autonomous is vastly enhanced.”
He pointed out that in a similar way, a combination of cameras and IR LEDs can be used for lane detection, and like the use of IR LEDs for pedestrian detection, using IR LEDs can greatly improve the performance and field of view (ability to detect objects) of cameras installed in cars as part of ADAS. And because such IR LEDs are installed in the headlamps, the fact that they are invisible to the naked eye at a distance ensures that they do not conflict with Federal automotive regulations.
Why IR LEDs for ADAS Next to Headlights Need So Much Power
Rajeev explained, “Power needed is proportional to the square of the distance (range) and area. It is also dependent on the reflectivity of the object (metal car reflects >80% of light; black tire < 10%). So, to reach a long range (200m) and a low reflectivity object (large black tire piece on road) you need higher power.”
Also in the same way such IR LEDs can improve night vision cameras for ADAS.
IR LEDs come in two primary wavelengths at Osram Opto Semiconductors 850 nm and 940nm.
Rajeev noted that the red glow from 850 nm wavelength IR LEDs is visible to the human eye at close range but camera image sensors have a higher sensitivity to IR LEDs with the 850nm wavelength than they do with 940 nm wavelength IR LEDs. He said in the email, “Since the LED is directed outside the vehicle, its red glow is not noticeable, especially when washed with white visible light, and 850nm is a preferred wavelength. In addition, 850nm is one of the wavelengths where the ambient noise from the sun is low, so the signal or image quality is better.”
On the other hand, the IR LEDs with the 940 nm wavelength are not visible to humans even at close range. This invisibility makes them ideal for passenger and driver status detection within a vehicle.
He stated, “The infrared LED (IRED) provides illumination for the camera to work (the camera is typically sensitive only to infrared light). This is because you do not want to shine visible light on the drivers face at nighttime, which could create glare and distract the driver.”
He pointed out that cabin monitoring works the same way except that a camera is pointed away from the driver toward where other passengers sit in the vehicle. He also said that gestures are recognized from the images taken by the infrared camera.