Infrared light is a type of light that is widely present in nature, including sunlight, and its characteristics are utilized in a variety of applications. In particular, detection methods using infrared light are becoming popular for sensing applications, and it is important to correctly understand the characteristics of infrared light when designing these systems.
This article explains the basic concepts of infrared light, the characteristics of infrared LEDs, and their applications.
Understanding these will provide you with a guide for selecting components when developing products that use infrared light or infrared LEDs.
Overview and characteristics of infrared light
What is infrared light?
Infrared light has a longer wavelength than visible light. The wavelength range from approximately 780 nm to 1 mm is called infrared light.
The longer the wavelength of light, the lower the energy of that light, so it has less impact on living organisms and the environment compared to blue light, which has a shorter wavelength. Furthermore, because it is invisible to the human eye, it prevents visual interference and is used as a sensing light source in small spaces or at night. Some of OTHERS representative features are described below.
Figure 1: Infrared light region
Characteristics of infrared light
The typical characteristics of infrared light are shown below.
Infrared light in nature
Infrared light exists in nature as part of sunlight, and is spread throughout the Earth's surface and atmosphere. The spectrum of sunlight is as shown in the figure, but you can see that some of the spectrum is lower on the Earth's surface than in outer space.
This is because some of the light is absorbed and scattered by the atmosphere as it travels from space to the Earth's surface.
Figure 2: Solar spectrum
Radiant heating
When infrared light is absorbed by a substance, it becomes kinetic energy such as the vibration and rotation of atoms and molecules.
The kinetic energy generated by this process manifests as a rise in temperature, so when infrared light is irradiated onto skin or clothing, you can feel the warmth.
Light Safety
JIS C 7550 is a standard for evaluating the effects of light on the human body, including on the eyes and skin. In this standard, the risk coefficient for infrared light is set lower than that for blue light, which shows that infrared light has a smaller effect on the irradiated object than blue light.
Overview and features of infrared LEDs
What is an infrared LED?
The three most common colors of LED light are red, blue, and green, but infrared LEDs that emit infrared light are also widely used.
The mainstream lighting wavelengths are around 850nm and 940nm, but there are also other wavelengths available depending on the application. Like visible light LEDs, there are an increasing number of products that are easy to light and have high output, but care must be taken as output reduction due to heat is noticeable.
Characteristics of infrared LEDs
The typical features of infrared LEDs are shown below.
Light-emitting device materials
Light-emitting elements that emit light in the yellow to red wavelength range, including infrared LEDs, are made from four types of compound semiconductors.
There are several combinations of compound semiconductors, but the most representative is the AlGaAs combination of Al (aluminum), Ga (gallium), and As (arsenic). Epitaxial growth on a specific substrate produces light-emitting elements that emit infrared light.
Figure 3: Materials and light-emitting regions
Electrical characteristics
Compared to blue and green LEDs called InGaN, which are made up of the three elements In (indium), Ga (gallium), and N (nitrogen), AlGaAs LEDs tend to have a lower VF (forward voltage). This is mainly due to differences in the band gap of the material. Below are guideline values for band gap and VF.
| LED material system | Main luminous color | band gap | VF guideline |
|---|---|---|---|
| InGaN | Blue, green, white | Approximately 2.0 to 3.4 eV | Approximately 2.8 to 3.5V |
| AlGaAs | Red, infrared | Approximately 1.4~2.2eV | Approximately 1.8~2.2V |
Table 1: Materials and VF guideline values
Temperature characteristics
AlGaAs has a narrow band gap and is susceptible to changes with temperature, so its luminous efficiency decreases, especially at high temperatures where the band gap shrinks. InGaN is relatively stable with temperature changes and output does not decrease much with increasing temperature, but AlGaAs can experience a drop in output of several percent to 10% or more with each increase in temperature, so care must be taken with the usage environment.
Uses and applications of infrared light and infrared LEDs
Examples of using infrared light and infrared LEDs
Infrared light is widely used in a variety of fields, taking advantage of its characteristics of being invisible and having little impact on the human body or the external environment. Demand is also increasing for easy-to-use infrared LEDs to generate infrared light.
Here we will introduce some application examples of infrared light and infrared LEDs.
Infrared remote control
Although wireless remote controls have become more common recently, infrared remote controls that use infrared light for communication are still the mainstream.
They are widely used in home appliances such as televisions and lighting, and most of them use a combination of a 900nm band infrared LED and PHOTO DETECTORS (DIODES) as a light source. In many cases, bullet-shaped infrared LEDs are used, and the light spread angle is very narrow at around 20 to 30 degrees to efficiently irradiate light forward.
Surveillance Cameras
A typical product that uses infrared light is a surveillance camera.
During the day, images and videos are captured using sunlight, but for nighttime surveillance, infrared light, which is not perceptible to the human eye, is often used.
The light source mainly uses infrared LEDs with a wavelength in the 800nm band. This has a large effect on the sensitivity of the camera (CMOS image sensor), and the longer the wavelength, the more rapidly the sensitivity of the camera drops, so the 800nm band, which has high sensitivity within the infrared range, is suitable. The graph below shows reference values for camera sensitivity.
Figure 4: Reference sensitivity values for CMOS image sensors
DMS (Driver Monitoring System)
DMS is a system that constantly monitors the driver of a vehicle and issues a warning in the event of an abnormality, and uses an infrared LED as the light source. The wavelength band used is often the 900nm band, as this is a region that is less affected by sunlight.
Unlike surveillance cameras, this system operates day and night, so sunlight, especially during the day, is a significant source of disturbing light. However, the impact can be reduced by using infrared light in the 900nm band (see Figure 2), which has a low sunlight component at the Earth's surface. Camera sensitivity is lower in the 900nm band than in the 800nm band, but in recent years, high-output 900nm band LEDs have been released, making it possible to compensate for the reduced sensitivity on the camera side with the output of infrared LEDs.
Biometric Sensor
Many smartwatches have built-in biosensors that use red and infrared LEDs to measure blood oxygen levels.
The principle is that it measures whether the hemoglobin in the blood is bound to oxygen, and since the absorption rates of red light and infrared light are different, blood oxygen saturation is measured from the amount of reflected light.
Summary
In this article, we have explained the basics of infrared light and infrared LEDs, as well as some examples of their applications.
Technologies using infrared light and infrared LEDs are currently spreading rapidly and playing an important role in advanced sensing applications. We handle a wide range of LED products, including infrared LEDs, and can propose optimal solutions based on your application and specifications. Please feel free Inquiry if you are looking for a sensing light source.
We also publish technical columns on visible light and laser light sources, so please take a look.
We will be publishing technical columns on other wavelength bands and LEDs in the future, so please look forward to them.
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