What Is Infrared Light?

This is the Visible Spectrum (above). It's the only part of the Electromagnetic Spectrum that our eyes can visually recognize. The wavelengths of the visible spectrum range from 380 to 750 nanometers (nm). The shorter wavelength on the left-hand side of the spectrum (380nm) is recognized as Purple and the longer wavelength on the right-hand side of the spectrum (750nm) is recognized as Red. Our eyes can't see anything above or below this range. Anything under 380 nanometers is known as Ultraviolet (UV) light and anything above 750 nanometers is known as Infrared (IR) light.

There are also different categories of infrared light: near-infrared (750-2500nm), mid-infrared (2500-4000nm), and far-infrared (4000nm and above). Near-infrared and far-infrared have very different properties and uses.

For this post, let's start exploring "near-infrared" light through a very familiar example.

Introducing a State-of-the-Art "Near-Infrared" Device... The iPhone!!

To give you an idea of near-infrared applications in our daily lives, we've prepared an iPhone and a near-infrared camera.

Ta-da! We now have a near-infrared camera.

Now, back to the main subject. First, let's unlock this iPhone using Face ID. The moment we touch the power button, the iPhone is already unlocked, it happens so fast it barely feels like there's any authentication process at all. But if we look at the iPhone through our NIR camera… 

The Future: LiDAR and Autonomous Driving

In recent years, the automotive industry has reached a major turning point. Electric vehicles are one part of that shift, but the real breakthrough enabling humanity's dream of fully autonomous passenger vehicles has been the development of advanced sensor technology. One of the key technologies behind this is called "LiDAR."

LiDAR stands for "Light Detection and Ranging," though the "L" is sometimes said to stand for "Laser" instead, since that's the light source it uses.

Lasers are commonly used in distance-measurement devices, like the handheld rangefinders used by construction workers, golfers, and the military. When in use, the device emits a laser beam, and if that beam hits an object, the reflected light is received and measured. LiDAR applies this same concept, creating "point cloud data" by repeatedly firing thousands of lasers in a fraction of a second (think radar, but with invisible lasers). This makes it possible for LiDAR devices to effectively "see" the shape and distance of objects.

*Image of 3D Point Cloud Data

Now that we understand how LiDAR works, what factors matter most for using it effectively in autonomous vehicles?

For example, if the spacing between laser observation points is too wide, a narrow obstacle could slip between the beams and go undetected.

Effective range is also important. Considering the braking distance of a fast-moving car, accurate measurement out to at least 100 meters is required. However, the further the distance, the less light gets reflected back, and the harder it becomes to measure.

One way to address this is to increase the laser's output power, which increases the amount of reflected light and makes detection easier. However, this approach comes with a major problem: it can damage the human eye.

Most mainstream LiDAR devices currently use the NIR wavelength of 905nm, mainly for cost reasons. But this wavelength is close enough to visible light that it can damage our retinas, potentially leading to blindness. As a result, government regulations in recent years have pushed LiDAR toward the longer 1500nm NIR wavelength. Switching to 1500nm significantly reduces, if not eliminates, that risk to our eyes.

The main disadvantage of using 1500nm is cost. Most consumer-grade silicon sensors don't have the sensitivity needed to detect infrared light at 1500nm, so specialized sensors made from InGaAs (Indium Gallium Arsenide) are required instead, a material that alone costs several times more than silicon. For reference, a basic silicon-based automotive LiDAR system is estimated to cost around ¥100,000 or more. So the question becomes: how much would a high-precision, InGaAs-based LiDAR system running at 1500nm cost? Balancing that cost-versus-performance tradeoff is likely to be one of the keys to developing the future of autonomous vehicles.

We hope this post helped you learn a little about the wonderful world of infrared light and some of its applications.

And for anyone looking to reduce infrared reflections, check out our IR Flock Sheet, which absorbs over 99% of NIR light!